- Email: [email protected]
Quadriceps muscle strength and dynamic stability in elderly persons
Gait and Posture 10 (1999) 10 – 20 www.elsevier.com/locate/gaitpos
Quadriceps muscle strength and dynamic stability in elderly persons Donna Moxley Scarborough a,*, David E. Krebs a,b, Bette Ann Harris b a
Biomotion Laboratory, Massachusetts General Hospital, Ruth Sleeper Hall, Room 010, 40 Parkman Street, Boston, MA 02114, USA b MGH Institute of Health Professions, Boston, MA, USA Accepted 14 April 1999
Abstract Several measures of dynamic stability during two functional activities correlated to quadriceps femoris muscle strength. A total of 34 disabled elders (aged 60–88) living in the Boston area consented to maximum isometric quadriceps muscle strength testing, chair rise and gait analysis. During chair rise, quadriceps strength significantly correlated with maximum upper body vertical linear momentum, r=0.53, PB0.005, anterior posterior linear momentum, r= 0.38, PB 0.05, and the time to complete the chair rise, r= −0.48, PB0.05, n= 29. Stride length and gait velocity correlated (r= 0.56, P B 0.001 and r= 0.51, P B 0.002, n=34) with quadriceps muscle strength. The maximum range of whole body anteroposterior (A/P) linear momentum during gait also correlated with quadriceps strength (r=0.47, P =0.004, n = 31). Dynamic stability during chair rise and gait, at preferred speed, correlates directly with quadriceps femoris muscle strength in functionally limited elderly individuals. In our sample, elders performed one of three movement strategies to arise from a chair, and quadriceps strength did not statistically differ between the chair rise strategy groups. However, persons with the greatest quadriceps strength values were more stable regardless of which chair rise strategy they performed. Our data indicate that clinicians should not suggest that patients use compensatory momentum inducing locomotor strategies unless the patient has sufficient strength to control these induced forces. © 1999 Elsevier Science B.V. All rights reserved. Keywords: Quadriceps muscle strength; Dynamic stability; Chair rise; Strategies; Gait; Elderly
1. Introduction Falls among the elderly are common and often result in injuries requiring hospitalization. Falls occur most frequently during walking, followed by locomotor activities of daily living, such as getting up from a chair [1]. A critical component in the safe performance of daily activities is dynamic stability, the ability to control the center of gravity (CoG) within and outside the base of support (BoS) [2,3]. The poor dynamic stability observed in many elderly individuals may commonly result from a combination of chronic deterioration of musculoskeletal, neuromuscular and somatosensory systems, caused by genetic traits, lifestyle and other factors [4,5]. The relationship of muscle strength to * Corresponding author. E-mail address: [email protected] (D. Moxley Scarborough)
detailed analysis of dynamic stability, for example trunk and CoG movement and the momentum generation during chair rise and walking in elderly individuals is essential to determine which muscles exert the most influence on dynamic stability. Based upon studies which identify those muscles most critical for dynamic stability during routine activities of daily living, such as arising from a chair, care providers can develop more rational approaches to treatment for reducing the likelihood of falls in at-risk individuals. Several investigations stress the importance of quadriceps muscle strength in older persons for the successful performance of chair rise and gait [5–12]. Timed sit to stand tests can estimate quadriceps strength, but do not quantify dynamic stability during the task [10,11]. Several investigators have contributed a variety of detailed kinematic and kinetic data during chair rise with self selected feet and arm positioning and with constrained arm and feet positions [9,13–
0966-6362/99/$ - see front matter © 1999 Elsevier Science B.V. All rights reserved. PII: S 0 9 6 6 - 6 3 6 2 ( 9 9 ) 0 0 0 1 8 - 1
D. Moxley Scarborough et al. / Gait and Posture 10 (1999) 10–20
19].One investigation has shown that quadriceps muscle strength is critically important to develop the moment across the knee that is necessary to enable functionally limited elders to arise from a chair [9]. Recently, Schenkman et al. confirmed the relationship of required lower extremity strength to performance of successful chair rise with challenging the subjects with lowering chair heights [20]. In this particular study the investigators found a significant correlation between combined lower extremity peak torque strength values and functional reach, r =0.47, P =0.001 [20]. However, to our knowledge there has been no report on the relationship of kinematic or kinetic data, measuring dynamic stability, during chair rise to specific muscle strength measurements. Correlations to dynamic stability measures such as time-distance parameters including stride length, gait velocity and double support time to lower extremity muscle strength have been investigated during gait [2,10–12,21–24]. However, we have not found reports on the relationship of leg muscle strength and whole body CoG momentum as a measure of dynamic stability, during gait. The ability to generate and control segmental and whole body momentum is a prerequisite for movement. Therefore, we believe momentum plays an intricate role in dynamic stability as it influences ‘‘the ability to control the center of gravity (CoG) within and outside the base of support (BoS)’’ [2]. The coordination of internal forces, such as muscle and ligament forces, and the influence of external forces, such as gravity, impacts the ability to control momentum. Including momentum as a measure of dynamic stability should provide information about locomotor dynamics. Past studies of momentum generation have primarily focused on describing movement patterns during chair rise [14–16]. Recently, Kaya and colleagues investigated momentum control during chair rise and gait among healthy elders and elders with bilateral vestibular hypofunction [25]. These investigators suggested healthy elders limit the speed of rising from a chair and gait velocity to lessen momentum generation because of limits in balance control or strength which are needed to dissipate momentum generated by faster gait velocity [25]. The previous studies have not correlated dynamic stability measures such as momentum generation to specific muscle strength measures. The influence of specific muscles’ strength on dynamic stability, and on safe performance of these activities, deserves further investigation. Clinicians frequently suggest different movements to compensate for weakness. For example, during chair rise clinicians often advise the use of repeated forward trunk flexion, referred to as ‘rocking’, to build momentum to assist with lift-off during chair rise. A weaker individual may not be capable of safely controlling the momentum generation creating loss of dynamic stability and resulting in a failed chair rise,
11
stumbling forward or falling backward into the chair [19,25]. The continuous firing pattern of the quadriceps during chair rise has been reported [17]. Resisted exercise training can significantly improve quadriceps strength among elderly persons [11]. Therefore, we investigated the role quadriceps muscle strength plays in dynamic stability during chair rise and gait. We have focused on the influence of the upper body (encompassing the pelvis and all segments superior) during chair rise to include the most dynamic movements of body mass being translated and rotated over the fixed feet. The upper body demonstrates the greatest variation in movement patterns during chair rise [15,20]. Therefore, the use of upper body measurements could provide more comprehensive information on dynamic stability during chair rise. During gait we expected to see persons with weaker quadriceps strength compensate by implementing a larger range of momentum generation, to assist in the development of speed and movement. We hypothesized that quadriceps strength correlated: (1) inversely with chair rise cycle time, maximum trunk flexion, maximum range of lateral trunk flexion, upper body anteroposterior (A/P) linear momentum and whole body CoG to ankle A/P difference at lift-off during chair rise; (2) directly with chair rise maximum upper body vertical linear momentum; (3) directly with gait stride length, average velocity, and center of pressure (CoP)-CoG moment arm (defined in Section 2); and (4) inversely with gait double support time and range of whole body CoG lateral and A/P linear momentum.
2. Methods
2.1. Subjects Of 50 possible subjects, 34 participants met the inclusion/exclusion criteria. The subjects ranging in age from 60 to 88 years, were involved in the Strong-for-Life in-home, resistance strength training study [25]. All subjects provided written informed consent and Table 1 provides characteristic data of all the participants from our sample of convenience. To be selected each participant had to indicate that their health status limited their ability to perform one or more functional activities (Table 1), but be able to both follow commands and ambulate independently for 25 feet [26]. Each participant received medical approval from their primary care physician and each passed an in-home safetyexercise test which monitored heart rate, blood pressure, and respiratory rate during a series of exercises. Excluded were subjects with terminal illness, neurologic disease, diabetes mellitus, major loss of vision (legally blind), and painful or gross musculoskeletal
D. Moxley Scarborough et al. / Gait and Posture 10 (1999) 10–20
12
structural abnormalities (joint deformity such as in rheumatoid arthritis).
2.2. Instrumentation Strength measurements were performed at each subject’s home with a hand-held Nicholas MMT Dynamometer (Model c 01160; Lafayette Instrument). The total body biomechanical analysis was performed at the Massachusetts General Biomotion Laboratory. Kinematic and kinetic data acquisition is described in detail elsewhere [8,27,28]. The instrumentation included: two Kistler piezoelectric force plates, two computer terminals, four Selspot II™ optoelectronic
cameras; and 64 infrared light emitting diodes (irLEDs). The irLEDs are mounted on 11 plastic arrays attached securely to the following respective body segments of each participant: right and left feet, shanks, thighs and arms, pelvis trunk and head (Fig. 1). TRACK™, PVWAVE and SuperPlot II software were used for data collection, processing and analysis. Subjects performed the chair rise activity on an armless, backless, height adjustable chair [27]. The array position and orientation data were converted into body segment positions yielding 6 df for each of the 11 body segments and a three-dimensional android model (Fig. 4) [27]. The instrumentation and processing of raw kinematic data yields resolutions of B 1° and B1 mm
Table 1 List of subject characteristicsa Subject ID no.
Age (years)
Gender
Functional limitationb
Height (m)
Weight (kg)
Quadriceps MVIC strength (kg-Output/ kg-BW)
Leg tested
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 n= 34
65.42 80.00 75.75 75.66 68.92 82.83 64.83 70.08 81.66 66.16 75.42 88.08 67.92 68.75 85.92 65.58 67.16 80.33 72.50 68.16 77.83 66.00 88.42 83.50 70.25 79.00 65.41 67.42 81.50 79.20 73.66 73.58 60.25 72.17 x¯ = 73.80 (7.48)
F M F F M M F F F F M F F F M M F F M F M F F F F F F F F F F F F M F= 25, M= 9
c,f b,c,d,e a,b,e a,b,c a,b c a,b,c,e c,e a–i b–d,f,g,i c a–d,f a–e a–f c a–d,f,g a–f a,e a,c,f,g a,b e e a–f a–g,i a–i a–g,i a–e a–c,e–h b,c,e,f a–g a–g a,be–h c,d f
1.52 1.66 1.56 1.57 1.63 1.65 1.65 1.50 1.55 1.60 1.83 1.57 1.51 1.57 1.83 1.70 1.73 1.65 1.73 1.57 1.91 1.57 1.70 1.50 1.73 1.56 1.60 1.57 1.63 1.56 1.70 1.50 1.66 1.84 x¯ = 1.64 (0.11)
52.27 87.73 61.36 59.09 65.91 85.91 66.36 68.64 72.73 68.18 86.36 57.73 58.18 79.55 59.09 90.91 92.27 75.00 59.09 47.73 79.55 77.27 69.09 54.09 67.27 63.64 55.91 102.73 63.64 56.36 93.18 77.27 84.09 84.09 x¯ =26.67 (4.99)
8.70 (0.00) 8.29 (0.15) 8.37 (0.52) 10.19 (0.16) 11.76 (0.05) 7.91 (0.26) 17.23 (1.21) 5.73 (0.14) 9.81 (0.35) 10.27 (0.38) 6.82 (0.63) 11.06 (0.72) 10.51 (0.17) 10.71 (0.20) 11.92 (1.41) 5.8 (0.21) 4.66 (0.38) 13.97 (1.93) 15.15 (1.41) 8.33 (0.34) 13.31 (0.65) 4.12 (0.17) 5.53 (0.56) 5.88 (0.48) 4.90 (0.14) 7.14 (0.00) 13.86 (0.40) 7.10 (0.09) 6.5 (0.51) 12.46 (0.74) 3.68 (0.60) 0.54 (0.07) 5.35 (0.08) 11.38 (0.88) x¯ =8.79 (3.71)
R R L R R R R R R R R R R R L R R R R R R R R L R R R R R R R L R R R =30, L= 4
a
Standard deviations in parentheses. List of functional limitations, based on health status, include subject responding as either ‘limited a little’ or ‘limited a lot’ to one or more of the following: (a) moderate activities, such as moving a table, pushing a vacuum cleaner, bowling or playing golf; (b) lifting or carrying groceries; (c) climbing several flights of stairs; (d) climbing one flight of stairs; (e) bending, kneeling or stooping; (f) walking more than a mile; (g) walking several blocks; (h) walking one block; (i) bathing or dressing yourself. b
D. Moxley Scarborough et al. / Gait and Posture 10 (1999) 10–20
Fig. 1. Subject with testing arrays in chair rise test position.
[27,28]. Upper body (head, arms, trunk and pelvis) and whole body linear momentum values were calculated as the product of each segment’s mass times the segment’s CoG velocity (momentum=mass times velocity, kgM/ s)] [8]. Segmental mass estimations and kinematic data are used to calculate the CoG of each segment and all segments are used to calculate whole body CoG [27]. Kinetic data including vertical reaction forces, and center of pressure (CoP) were measured from the force plates [27].
2.3. Protocol Subjects’ muscle strength was assessed at each participant’s home within 2 weeks prior to the Biomotion Laboratory tests. Quadriceps muscle strength was measured by a single tester. Strength was defined as the force generated during a maximum voluntary isometric contraction (MVIC) measured in kilograms (kg) with a hand held dynamometer during a 3-s isometric hold at 60° knee flexion; the participant was seated in a chair with feet on the floor [26]. The dynamometer was calibrated at 90.50 kg prior to each test and was placed against the right shin two finger widths (about 5 cm) above the malleoli. The subject was asked to ‘‘push
13
as hard as you can into me’’. The right knee was chosen for consistency across subjects; however, left knee measurements were collected from four subjects, who were fearful of potential right knee pain during quadriceps muscle strength testing. An initial practice measurement was performed followed by two recorded strength measurements. The two recorded MVIC values were each divided by the individual’s weight [29]. The average of the two values was used in the statistical analysis. All participants were barefoot during chair rise and gait tests. For each chair rise trial the participant was seated with the greater trochanters approximately 4 cm from the front edge of a backless chair, adjusted to 100% knee height, measured as the distance from the right medial tibial plateau to the floor. Each subject performed one practice and two recorded trials. Each participant placed their feet as requested in a self constrained position, 10 cm apart, with 18° of ankle dorsi flexion. Trials were considered successful when participants kept their arms folded in a constrained position in front of their abdomen and their feet remained still during the chair rise. Each participant was asked to arise from the chair as they ‘normally do’ beginning on ‘go’ after the cue ‘one, two, ready, go’. Data collection began on ‘ready’ and once the subject stood upright, s/he looked straight ahead and stood as still as possible during the remaining portion of the total 7-s data collection period. Arm and foot position constraints were used to improve the consistency of the body position during chair rise testings [14,18]. A total of 29 subjects were able to arise independently, without taking a step or unfolding their arms, at 100% knee height, but five subjects were unable to arise from the 100% knee height chair without using their arms to push up or assistance from the tester; they repeated the same protocol with a 120% knee height chair. The variables chosen to measure dynamic postural stability during chair rise were analyzed only for subjects able to perform chair rise at 100% knee height. From start of movement (SOM) to end of rise (EOR) we analyzed maximum upper body vertical and anteroposterior linear momentum, maximum trunk flexion (measured relative to room coordinates) and maximum range of lateral trunk flexion. These measures were collected between the SOM time and EOR time of chair rise as defined in Fig. 2. The chair rise cycle time was also calculated for all subjects as the time from SOM through EOR. The A/P difference between the CoG and the ankle joint (the average of the left and right ankle joint centers’ positions) in the sagittal plane at the time of lift-off from the chair was normalized to the A/P difference of CoG to ankle joint at the end of rise for each individual. This value was then normalized to each individual’s height in meters. For each gait trial the subject walked approximately 8 m. Data collection began when each subject entered
D. Moxley Scarborough et al. / Gait and Posture 10 (1999) 10–20
14
whole body CoG anteroposterior (A/P) linear momentum (the absolute difference between the maximum and minimum anteroposterior linear momentum values during a gait cycle), and range of whole body CoG lateral linear momentum (the absolute difference of the maximum right and left lateral momentum values, during a gait cycle).
2.4. Data analysis The average value for all data from two trials was analyzed. Means, standard deviations, and linear correlation analyses were performed for all data. Pearson product-moment correlations between quadriceps strength and all the dynamic stability variables for chair rise and gait were performed to test each hypothesis. For analysis of group differences between chair rise strategy groups to be more conservative an ANOVA (two-tailed) was performed. Statistical significance of correlations and group differences was determined at PB 0.05. Fig. 2. The determination of chair rise events. (A) Start of movement (SOM), defined as the time at which forward upper body momentum begins (vertical line labeled ‘S’). (B) Lift-off (LO), defined as the time at which the thigh segment moves upwards from its original position by 2° (vertical line labeled ‘L’). (C) End of rise (EOR), defined as the time at which the upper body CoG reaches its highest vertical position (vertical line labeled ‘E’).
the 2 × 2 ×2-m viewing volume, approximately 3 m beyond the starting point. Each subject was asked to ‘‘move forward in as straight a line as possible, walking at your normal pace, as if you were taking a brisk walk in the park’’. The following gait variables were determined: stride length (distance traveled between consecutive ipsilateral heel strikes), gait velocity (average whole body CoG velocity during one gait cycle), double support time (one of the two periods of time during which the body is supported by both limbs, expressed as % of the gait cycle), maximum moment arm (the distance between the whole body CoG and CoP, in both the anteroposterior and medial lateral planes during single limb stance phase) [17], range of Table 2 Normalized quadriceps muscle strengtha values Subjects
n
Mean
S.D.
Range
Performed CR at 100% knee height Performed CR at 120% knee height Unable to perform CR
29
9.58
3.33
4.12–17.23
4
5.18
1.26
3.68–5.88
1
0.54
a
Strength equals the total output of knee extension strength in kg divided by total body weight in kg (kg-output/kg-BW). CR, chair rise.
3. Results
3.1. Quadriceps muscle strength The weight adjusted quadriceps strength for all subjects ranged from 0.54 to 17.23 kg per kg of body weight (Table 2).
3.2. Relationship of quadriceps muscle strength to measures of dynamic stability during chair rise Quadriceps strength had a significant, moderately strong correlation with maximum upper body vertical linear momentum, (r=0.53, PB 0.005) and there also was a significant direct correlation with maximum upper body anteroposterior (A/P) linear momentum, (r= 0.38, PB0.05), (Fig. 3). Fig. 3C demonstrates that as the strength of the quadriceps muscle increased, the faster each subject could arise from the chair. There was a significant inverse correlation between quadriceps muscle strength and chair rise cycle time (r= − 0.48 and PB 0.05). The participant with the least quadriceps muscle strength (0.54 kg, S.D.= 0.07) was unable to perform chair rise at either 100% or the increased seat height of 120% of knee height. There were four other elders with low values of knee extensor strength who were unable to perform chair rise with the seat of the chair at 100% of knee height but could arise from the chair with the seat at 120% of knee height. The whole body CoG to ankle A/P difference at lift-off did not correlate with quadriceps strength (r= − 0.07, P= 0.37).
D. Moxley Scarborough et al. / Gait and Posture 10 (1999) 10–20
15
3.3. Mo6ement strategies of chair rise During chair rise subjects used three major movement patterns, or strategies. The most frequently observed was the momentum-transfer chair rise strategy (Fig. 4) first described by Schenkman and colleagues [15,16]. Elders in our study also performed the exaggerated trunk flexion chair rise strategy (Fig. 5), described previously and referred to as the stabilization strategy by Hughes and Schenkman [15]. The third strategy we observed has not previously been reported. The dominant vertical chair rise strategy is described in detail in Fig. 6. The subjects in this sample consistently performed the same strategy for each of the consecutive two chair rise trials. Table 4 presents descriptive findings of average quadriceps strength values and subject characteristics for each of the three chair rise strategy groups. There was no statistically significant differences in quadriceps strength across groups, P= 0.99.
3.4. Relationship of quadriceps strength to dynamic stability during gait
Fig. 3. Relationships between relative quadriceps muscle strength (kg-Output/kg-BW) and dynamic stability during chair rise. (A) The linear relationship between relative quadriceps muscle strength and maximum upper body vertical linear momentum during chair rise (r = 0.53, P B 0.005). (B) The linear relationship between relative quadriceps muscle strength and maximum upper body A/P linear momentum (r= 0.38, P B0.05). (C) The linear relationship between quadriceps muscle strength and chair rise cycle time (r = −0.48, P B0.01). The bold lines represent the regression lines and the dashed lines show the 95% confidence interval ranges (n= 29).
Trunk motion during chair rise was not significantly related to knee extensor strength. Quadriceps muscle strength was not correlated with either maximum trunk flexion (r= − 0.13, P = 0.4874) or range of lateral trunk flexion, (r= − 0.097, P =0.6165). Table 3 summarizes the correlations of the measures of dynamic stability during chair rise.
As hypothesized, quadriceps strength had a significant, moderately high correlation with stride length (r=0.558, PB 0.001) and preferred gait velocity (r= 0.51, PB0.002) (Fig. 7). Double support time correlated inversely with quadriceps strength (r= −0.41, PB 0.02). Maximum moment arm had a lower but positive correlation with quadriceps muscle strength (r=0.35, PB 0.05). The range of the whole body CoG A/P linear momentum values correlated directly with quadriceps strength (r= 0.47, P= 0.004, n= 31). There was no statistical correlation between quadriceps strength and maximum range of whole body lateral linear momentum (r= 0.25, P=0.08, n= 33). Table 5 summarizes the correlations among the measures of dynamic stability during gait.
3.5. Effect of age on quadriceps strength and measures of dynamic stability during chair rise and gait Age did not predict quadriceps muscle strength (r= 0.0843, P= 0.6638). Of the 34 subjects examined, 19 were young elderly (60–75 years) and 15 were old elderly ( \ 75.1 years). The subject who was unable to perform chair rise at 100 or 120% knee height was in the young elderly group. Of the persons requiring the increased 120% knee height chair, half were in the young elderly group and the other half in the old elderly group. Of the persons who were able to successfully arise from a chair at 100% knee height, 16 were in the young elderly and 13 were in the old elderly age groups. Age did not correlate significantly with measures of dynamic stability during gait or chair rise.
16
D. Moxley Scarborough et al. / Gait and Posture 10 (1999) 10–20
Table 3 Linear correlations of dynamic stability measures during chair rise
Upper body A/P linear momentum Upper body vertical linear momentum Chair rise cycle time Maximum trunk flexion
Upper body vertical Chair rise linear momentum cycle time
Maximum trunk flexion
Range of lateral trunk flexion
CoG to ankle A/P difference
r=0.67, P= 0.0001* r = −0.28, P= 0.074
r = 0.37, P =0.03* r=−0.01, P =0.48 r =0.08, P =0.34
r= −0.71, P =0.0001* r=−0.04, P=0.42 r =−0.14, P = 0.22 r=−0.02, P =0.46 r = 0.42, P =0.01* r= 0.25, P = 0.09 r =0.29, P= 0.13
r =−0.02, P = 0.45 r=−0.14, P =0.23
* Correlation reaches level of significance.
4. Discussion Development of effective strengthening treatment programs for prevention of falls and maintaining safe, independent function among elderly persons depends on determination of how specific muscle strength influences dynamic stability during the common activities of arising from a chair and walking. We focused on the quadriceps femoris muscle strength because of its large size, ease of testing and known association of power generation during chair rise [10,11,15,17,21]. The detailed biomechanical analysis of several dynamic stability measures allowed us to discover the important role quadriceps muscle strength plays in dynamic stability during chair rise and during gait among elderly persons. Contrary to clinical wisdom and our hypothesis, during chair rise our elderly subjects used momentum differently than expected, demonstrating three strategies to accomplish chair rise, independent of quadriceps muscle strength (Table 4). During chair rise some elders avoid the potentially destabilizing, but more functional, momentum transfer strategy, apparently because they lack the coordination and/or strength in muscle groups other than the quadriceps needed to dampen and control the increased forces induced by the rapid movement resulting from momentum generation. However, persons with the greatest quadriceps strength values typically performed chair rise faster and generated greater vertical and A/P linear momentum, demonstrating better stability and ability to control movement, regardless of which chair rise strategy they performed. These findings suggest that clinicians caring for elderly persons should monitor quadriceps strength and recommend quadriceps strengthening exercises for maintaining and improving dynamic stability. Having normal quadriceps strength is important in maintaining dynamic stability during the common activity of arising from a chair. Schenkman and colleagues described four phases of chair rise during two strategies of chair rise [14,15,18]. The momentum-transfer chair rise strategy was observed in healthy/normal subjects and the stabilization strategy was observed in
functionally impaired elderly subjects [14,15,18]. Investigators established the importance of quadriceps strength for successful chair rise, especially from low chair heights, among healthy adults and functionally impaired elders [9,22].
Fig. 4. Momentum-transfer chair rise strategy. At time of lift-off, the upper body anterior momentum transfers to total body vertical momentum with continued anterior momentum [16,17]. The following is our kinematic description of the momentum-transfer strategy, to assist the clinician when observing persons: at the time of lift-off upper body flexion continues with initiation of knee extension which smoothly transitions to simultaneous back and knee extension, until erect posture is attained. (The vertically directed line originating from the force plates within the floor represents the ground reaction force. The cross seen at the level of the pelvis represents the whole body CoG.)
Fig. 5. Exaggerated trunk flexion chair rise strategy. The exaggerated trunk flexion chair rise strategy has been described previously and referred to as the stabilization strategy [8,17]. We have expanded the description as: exaggerated trunk flexion prior to lift-off, frequently followed by further trunk flexion, placing the CoG over the feet resulting in delayed trunk extension during the final transition to the erect posture. (The vertically directed line originating from the force plates within the floor represents the ground reaction force. The cross seen at the level of the pelvis represents the whole body CoG.)
D. Moxley Scarborough et al. / Gait and Posture 10 (1999) 10–20
Fig. 6. Dominant vertical rise chair rise strategy. The dominant vertical chair rise strategy is described as follows: at time of lift-off, upper body anterior momentum lessens and cessation of forward trunk flexion immediately follows with subsequent dominance of vertical momentum and knee extension. (The vertically directed line originating from the force plates within the floor represents the ground reaction force. The cross seen at the level of the pelvis represents the whole body CoG.)
We found a strong correlation between quadriceps muscle strength and maximum upper body vertical linear momentum during chair rise. Quadriceps muscle contraction creates the necessary vertical velocity, which in turn determines the vertical linear momentum of each person as they arise from a chair. We also found quadriceps muscle strength correlated inversely with chair rise cycle time. These observations confirm and extend previous conclusions, that the time required to arise from a chair provides a good indirect measurement of knee extensor strength [10,11]. In contrast to our original hypothesis, lateral trunk flexion during chair rise does not correlate with quadriceps muscle strength. We hypothesized that persons with stronger quadriceps would demonstrate greater dynamic stability and thus have less lateral instability. Persons with weak quadriceps muscles may also have weakness in lateral and other proximal stabilizing muscles, potentially leading to lateral instability. However, the predominant anteroposterior (A/P) direction of movement that occurs during chair rise leads to instability primarily in the same A/P direction, not to lateral
17
instability [19]. Future investigations such as the relationships of lateral trunk flexion and lateral center of gravity displacement during chair rise to the strength of the hip abductors and ankle everters, may help to establish if these muscles, in addition to the quadriceps femoris, have a primary role in dynamic stability during chair rise. We also hypothesized that the weaker elderly participants would generate greater A/P momentum to assist with lift-off, to compensate for their decreased strength. Instead, quadriceps muscle strength correlated directly with maximum upper body A/P linear momentum. There are at least two explanations for this unexpected finding. First, stronger persons are better able to generate a greater velocity on arising, thus creating higher momentum. Second, and more interestingly, the weaker elders, in general, do not attempt to generate greater A/P momentum as a compensatory strategy. This is probably because they lack the strength to control increased forces. We had expected, as suggested by previous investigators, that weaker participants would increase trunk flexion prior to lift-off in order to position their CoG over their ankles and to generate momentum [14,18]. The exaggerated trunk flexion strategy was performed by several participants in our investigation, however, their quadriceps muscle strength ranged from low to high values. Some of the elderly participants in our study used the dominant vertical chair rise strategy, and these elderly individuals also have values of quadriceps muscle strength ranging from low to high values. Surprisingly, certain weaker elderly participants use this strategy, despite the increased leg muscle effort required and the apparent energetic inefficiency of this movement strategy to arise from a chair. Several investigators have suggested that the whole body CoG to ankle position A/P difference at lift-off varies with the movement strategies of chair rise [3,15]. We did not find a statistically significant correlation between quadriceps strength and whole body CoG to ankle position A/P difference
Table 4 Chair rise strategy groups with respective quadriceps strength values and subject characteristics
Momentum transfer strategy
Exaggerated flexion strategy
Dominant vertical rise strategy
Mean (S.D.) Range Mean (S.D.) Range Mean (S.D.) Range
n
Quadriceps strengtha
Age (years)
Height (m)
Weight (kg)
17
9.62 (3.59) 5.35–17.23 9.71 (3.74) 4.90–13.31 9.42 (2.99) 4.12–13.97
72.63 (8.58) 60.25–88.42 74.86 (8.97) 65.42–85.92 74.47 (5.34) 66.00–81.66
1.61 (0.067) 1.50–1.73 1.75 (0.165) 1.52–1.91 1.64 (0.121) 1.55–1.84
69.89 (15.08) 47.73–102.73 64.55 (11.73) 52.27–79.55 74.43 (9.85) 59.09–86.36
4
8
a Quadriceps muscle strength values [(kg-output/kg-BW)100]. There was no statistical difference in quadriceps strength between chair rise strategy groups (ANOVA, P=0.958).
18
D. Moxley Scarborough et al. / Gait and Posture 10 (1999) 10–20
Fig. 7. Relationships between relative quadriceps muscle strength (kg-Output/kg-BW) and dynamic stability during gait. (A) Relationship between relative quadriceps muscle strength and stride length (r= 0.56, P = 0.001, n = 34). (B) Relationship between relative quadriceps muscle strength and gait velocity (r = 0.51, P= 0.002, n =34). (C) Relationship between relative quadriceps muscle strength and the maximum range of whole body A/P linear momentum (r= 0.47, P =0.004, n = 31). The bold lines represent the linear regression lines and the dashed lines show the 95% confidence interval ranges.
at lift-off. These data suggest that quadriceps femoris muscle strength alone does not determine the strategy for arising from a chair in functionally limited elderly persons. The reasons accounting for the different strategies used to arise from a chair in our study group require further investigation. Participants who are unable to arise from a chair at 100% of their knee height have failed in their attempt while using one of the above
three strategies. Stepping forward, backwards or falling back onto the seat (sit-back) are body reaction movements, that we have observed during failed attempts at arising from the chair [19]. These adjustments for positioning the body can sometimes lead to falls and injuries [1,19]. Continued investigations to determine which strategy provides the least likelihood of failure in arising from a chair among elderly persons with all ranges of quadriceps strength may be valuable to the clinician for designing preventative health programs for functionally limited, weaker, at-risk individuals. At present clinicians may instruct elderly persons to use greater momentum, or ‘rocking’, to assist in their liftoff during chair rise. The biomechanical analysis performed in our study suggests using great caution in offering this advise as it may inadvertently induce a person with weak quadriceps muscles to fall forward if the elder cannot control the increased momentum associated with this pattern of movement [19]. Muscle strength and motor control are also needed to dampen the effects of this additional generated momentum. Our data suggest that coordinated anteroposterior, then vertical momentum peaks are needed to successfully arise from a chair (Figs. 4–6). Our investigation further supports the importance of quadriceps strength to dynamic stability during gait. As hypothesized, stride length, gait velocity, and maximum moment arm correlated directly and double support time correlated inversely with quadriceps muscle strength. Similar findings from a previous investigation of 26 elderly persons demonstrated that quadriceps strength correlated significantly with step length (r= 0.69 PB 0.001) [21]. Our data also supported previous findings from larger sample sizes that stride length correlates directly with gait velocity [12,24]. Longer stride length obviates shuffling; shuffling is observed frequently in older persons and may also decrease falls which often occur during hurried gait or when turning in older individuals [1,30]. Creating longer strides allows a person to increase gait speed, which is important for independence. The ability of an elderly person to increase their walking speed to avoid a moving obstacle on the sidewalk (such as a person on roller skates, a dog, or a bicyclist etc.) or to cross a road quickly is an important safety issue among independent, community dwelling, elderly, persons. Our data indicate that elderly persons with greater quadriceps muscle strength had shorter double support time than weaker individuals. Double support time has been used as a parameter of dynamic stability by many investigators [2,7,23,24]. Elders with greater quadriceps strength values had larger maximum moment arm values during gait. Therefore, stronger elderly participants move their CoG farther away from their BoS, than the weaker participants. This demonstrates confidence in controlling the CoG beyond the BoS ‘comfort zone’
D. Moxley Scarborough et al. / Gait and Posture 10 (1999) 10–20
19
Table 5 Linear correlations of dynamic stability measures during gait
Stride length Gait velocity
Gait velocity
Double support time
Moment arm
Range of A/P momentum
Range of lateral momentum
r = 0.94, (n=34) P =0.0001*
r = −0.69, (n= 34) P= 0.0001* r= −0.70, (n= 34) P = 0.0001*
r = 0.82, (n =34) P = 0.0001* r= 0.80, (n =34) P= 0.0001* r=−0.44, (n = 34) P= 0.0099*
r = 0.14, (n = 34) P= 0.25 r =−0.05, (n =27) P= 0.41 r =−0.13, (n =27) P =0.26 r =−0.21, (n = 31) P= 0.13
r= 0.36, (n =34) P= 0.03* r =0.17, (n =29) P=0.19 r =−0.09, (n =29) P=0.32 r =0.24, (n = 33) P =0.09 r =0.20, (n =31) P=0.14
Double support time Maximum Moment arm Range of A/P momentum * Correlation reaches level of significance.
which is a primary skill required in dynamic stability. The relationship of quadriceps strength to maximum range of A/P linear momentum values during gait suggests greater quadriceps strength allows elderly persons the ability to generate greater forward momentum likely contributing to increased gait velocity. Persons with weaker quadriceps strength values did not develop high momentum values as a strategy to increase gait velocity, suggesting inability to control the additional forces that result from greater momentum generation. In activities such as walking, it appears that greater quadriceps muscle strength enhances dynamic stability and may play an important role in reducing the risk of falls and related injuries in functionally limited elderly individuals. Limitations of the present investigation include a modest sample size and a predominance of female participants. Strength measured in Newtons of force, as opposed to our kilogram units, might allow more direct comparison to results of other investigations that use force units. This study implemented a standardized, scientifically accepted isometric strength testing protocol, which has been used when correlating strength to functional tasks [26,29,31]. Further investigations of the correlations between quadriceps muscle strength and the strength of other muscles, such as the trunk extensors, the abdominal muscles, hip flexors, abductors and extensors, ankle plantar flexors, dorsi flexors, inverters and everters and measurements of dynamic stability during chair rise and gait should be carried out in a larger sample of functionally limited elders. The influence of exercise training, specifically quadriceps femoris muscle strengthening, on different measurements of dynamic stability among elderly individuals and the effects of such training on the frequency of falls and injuries, needs to be assessed. Nonetheless, our data represent the largest sample and most sophisticated analysis reported to date evaluating the relationship between strength and a variety of dynamic stability measurements during chair rise and gait.
5. Conclusions With these elders, increased generation of A/P momentum was not used as a compensatory strategy for weak quadriceps strength during chair rise or gait. The results of our investigation introduces clinical perspectives on three different movement strategies to accomplish chair rise among elders and the relationship of quadriceps strength to dynamic stability measures. Knee extensor strength correlates with most measures of dynamic stability during chair rise and gait. Our data indicate that clinicians should not suggest that patients use compensatory momentum inducing locomotor strategies unless the patient has sufficient strength to control these induced forces. Adequate quadriceps muscle strength is essential for the ability to successfully perform functional activities of arising from a chair and walking, as importantly, quadriceps strength enhances the generation and control of momentum and maintenance of good dynamic stability, ultimately influencing safety and the likelihood of falls, during these two locomotor activities of daily living.
Acknowledgements This research was supported by grants from the National Institutes of Health (R01AG12561 and P50 AG11669-03). We are grateful for the cooperation and assistance of New England Research Institute’s staff from its Roybal Center’s Strong for Life exercise project, and for the assistance from Massachusetts General Hospital Biomotion Laboratory staff, in particular Jose V. Ramirez, MD, for his edits and locomotor data collection. Acknowledgment and appreciation is extended to Patrick O. Riley, Ph.D. for his assistance during the initial phases of this research. An extended appreciation, from the first author, goes to my father, Richard T. Moxley III, MD for his dedication, guidance, research skills and encouragement.
20
D. Moxley Scarborough et al. / Gait and Posture 10 (1999) 10–20
References [1] Tinetti ME, Speechley M, Ginter SF. Risk factors for falls among elderly persons living in the community. N Engl J Med 1988;319:1701– 7. [2] Krebs DE, Lockert J. Vestibulopathy and gait. In: Spivach BS, editor. Evaluation and management of gait disorders. New York: Marcel Dekker, 1995:93–115. [3] Pai Y-C, Patton J. Center of mass velocity—position predictions for balance control. J Biomech 1997;30:347–54. [4] Horak FB, Shupert CL, Mirka A. Components of postural dyscontrol in the elderly: a review. Neurobiol Aging 1989;10:727 – 38. [5] Lord SR, Clark RD, Webster IW. Postural stability and associated physiological factors in a population of aged persons. J Gerontol Med Sci 1991;46:69–76. [6] Buchner DM, de Lateur BJ. The importance of skeletal muscle strength to physical function in older adults. J Behav Med 1991;13:91 – 7. [7] Wolfson L, Whipple R, Amerman P, Tobin J. Gait assessment in the elderly: a gait abnormality rating scale and its relation to falls. J Gerontol Med Sci 1990;45:M12–9. [8] Hutchinson EB, Riley PO, Krebs DE. A dynamic analysis of the joint forces and torques during rising from a chair. IEEE Trans Rehab Engin 1994;2:49–56. [9] Hughes MA, Myers BS, Schenkman ML. The role of strength in rising from a chair in the functionally impaired elderly. J Biomech 1996;29:1509–13. [10] Bohannon RW, Smith J, Hull D, Palmeri D, et al. Deficits in lower extremity muscle and gait performance among renal transplant candidates. Arch Phys Med Rehabil 1995;76:547–51. [11] Fiatarone MA, Marks EC, Ryan ND, Meredith CN, et al. High-intensity strength training in nonagenarians: effects on skeletal muscle. J Am Med Assoc 1990;263:3029–34. [12] Perry J, Mulroy SJ, Renwick SE. The relationship of lower extremity strength and gait parameters in patients with post-polio syndrome. Arch Phys Med Rehabil 1993;74:165–9. [13] Schultz AB, Alexander NB, Ashton-Miller JA. Biomechanical analyses of rising from a chair. J Biomech 1992;25:1383– 91. [14] Schenkman M, Berger RA, Riley PO, Mann RW, et al. Wholebody movements during rising to standing from sitting. Phys Ther 1990;70:638 – 48.
.
[15] Hughes MA, Schenkman ML. Chair rise strategy in the functionally impaired elderly. J Rehabil Res Dev 1996;33:409–12. [16] Pai Y-C, Naughton BJ, Chang RW, Rogers MW. Control of body centre of mass momentum during sit-to-stand among young and elderly adults. Gait Posture 1994;2:109 – 16. [17] Millington PJ, Myklebust BM, Shambes GM. Biomechanical analysis of the sit-to-stand motion in elderly persons. Arch Phys Med Rehabil 1992;73:609 – 17. [18] Ikeda ER, Schenkman ML, Riley PO, Hodge WA. Influence of age on dynamics of rising from a chair. Phys Ther 1991;71:473– 81. [19] Riley PO, Krebs DE, Popat R. Biomechanical analysis of failed sit to stand. IEEE Trans Rehab Engin 1997;5:353 – 9. [20] Schenkman M, Hughes MA, Samsa G, Studenski S. The relative importance of strength and balance in chair rise by functionally impaired older individuals. J Am Geriatr Soc 1996;44:1441–6. [21] Judge JO, Davis RB, Ounpuu S. Step length reductions in advanced age: the role of ankle and hip kinetics. J Gerontol Med Sci 1996;51A:303 – 12. [22] Imms FJ, Edholm OG. Studies of gait and mobility in the elderly. Age Ageing 1981;10:147 – 56. [23] Gill-Body KM, Krebs DE. Locomotor stability problems associated with vestibulopathy: assessment and treatment. Phys Ther Practice 1994;13:232 – 45. [24] Perry J. Gait analysis: normal and pathological function. Thorofare, NJ: SLACK, 1992:19 – 47 also pp. 287 – 97. [25] Kaya BK, Krebs DE, Riley PO. Dynamic stability in elders: momentum control in locomotor ADL. J Gerontol Med Sci 1998;53A:M126– 34. [26] Jette AM, Lachman M, Giorgetti MM, Assmann SF, et al. Exercise: it’s never too late!. Am J Public Health 1998;89:66–72. [27] Riley PO, Mann RW, Hodge WA. Modelling of the biomechanics of posture and balance. J Biomech 1990;23:503 – 6. [28] Antonsson EK, Mann RW. Automatic 6-D.O.F. kinematic trajectory acquisition and analysis. J Dyn Syst Meas Control 1989;111:31 – 9. [29] Andrews AW, Bohannon RW. Normative values for isometric muscle force measurements obtained with hand-held dynamometers. Phys Ther 1996;76:248 – 59. [30] Alexander NB. Gait disorders in older adults. J Am Geriatr Soc 1996;44:434 – 51. [31] Krebs DE, Jette AM, Assmann SF. Moderate exercise improves gait stability in disabled elders. Arch Phys Med Rehabil 1998;79:1489 – 95.
Quadriceps muscle strength and dynamic stability in elderly persons Donna Moxley Scarborough a,*, David E. Krebs a,b, Bette Ann Harris b a
Biomotion Laboratory, Massachusetts General Hospital, Ruth Sleeper Hall, Room 010, 40 Parkman Street, Boston, MA 02114, USA b MGH Institute of Health Professions, Boston, MA, USA Accepted 14 April 1999
Abstract Several measures of dynamic stability during two functional activities correlated to quadriceps femoris muscle strength. A total of 34 disabled elders (aged 60–88) living in the Boston area consented to maximum isometric quadriceps muscle strength testing, chair rise and gait analysis. During chair rise, quadriceps strength significantly correlated with maximum upper body vertical linear momentum, r=0.53, PB0.005, anterior posterior linear momentum, r= 0.38, PB 0.05, and the time to complete the chair rise, r= −0.48, PB0.05, n= 29. Stride length and gait velocity correlated (r= 0.56, P B 0.001 and r= 0.51, P B 0.002, n=34) with quadriceps muscle strength. The maximum range of whole body anteroposterior (A/P) linear momentum during gait also correlated with quadriceps strength (r=0.47, P =0.004, n = 31). Dynamic stability during chair rise and gait, at preferred speed, correlates directly with quadriceps femoris muscle strength in functionally limited elderly individuals. In our sample, elders performed one of three movement strategies to arise from a chair, and quadriceps strength did not statistically differ between the chair rise strategy groups. However, persons with the greatest quadriceps strength values were more stable regardless of which chair rise strategy they performed. Our data indicate that clinicians should not suggest that patients use compensatory momentum inducing locomotor strategies unless the patient has sufficient strength to control these induced forces. © 1999 Elsevier Science B.V. All rights reserved. Keywords: Quadriceps muscle strength; Dynamic stability; Chair rise; Strategies; Gait; Elderly
1. Introduction Falls among the elderly are common and often result in injuries requiring hospitalization. Falls occur most frequently during walking, followed by locomotor activities of daily living, such as getting up from a chair [1]. A critical component in the safe performance of daily activities is dynamic stability, the ability to control the center of gravity (CoG) within and outside the base of support (BoS) [2,3]. The poor dynamic stability observed in many elderly individuals may commonly result from a combination of chronic deterioration of musculoskeletal, neuromuscular and somatosensory systems, caused by genetic traits, lifestyle and other factors [4,5]. The relationship of muscle strength to * Corresponding author. E-mail address: [email protected] (D. Moxley Scarborough)
detailed analysis of dynamic stability, for example trunk and CoG movement and the momentum generation during chair rise and walking in elderly individuals is essential to determine which muscles exert the most influence on dynamic stability. Based upon studies which identify those muscles most critical for dynamic stability during routine activities of daily living, such as arising from a chair, care providers can develop more rational approaches to treatment for reducing the likelihood of falls in at-risk individuals. Several investigations stress the importance of quadriceps muscle strength in older persons for the successful performance of chair rise and gait [5–12]. Timed sit to stand tests can estimate quadriceps strength, but do not quantify dynamic stability during the task [10,11]. Several investigators have contributed a variety of detailed kinematic and kinetic data during chair rise with self selected feet and arm positioning and with constrained arm and feet positions [9,13–
0966-6362/99/$ - see front matter © 1999 Elsevier Science B.V. All rights reserved. PII: S 0 9 6 6 - 6 3 6 2 ( 9 9 ) 0 0 0 1 8 - 1
D. Moxley Scarborough et al. / Gait and Posture 10 (1999) 10–20
19].One investigation has shown that quadriceps muscle strength is critically important to develop the moment across the knee that is necessary to enable functionally limited elders to arise from a chair [9]. Recently, Schenkman et al. confirmed the relationship of required lower extremity strength to performance of successful chair rise with challenging the subjects with lowering chair heights [20]. In this particular study the investigators found a significant correlation between combined lower extremity peak torque strength values and functional reach, r =0.47, P =0.001 [20]. However, to our knowledge there has been no report on the relationship of kinematic or kinetic data, measuring dynamic stability, during chair rise to specific muscle strength measurements. Correlations to dynamic stability measures such as time-distance parameters including stride length, gait velocity and double support time to lower extremity muscle strength have been investigated during gait [2,10–12,21–24]. However, we have not found reports on the relationship of leg muscle strength and whole body CoG momentum as a measure of dynamic stability, during gait. The ability to generate and control segmental and whole body momentum is a prerequisite for movement. Therefore, we believe momentum plays an intricate role in dynamic stability as it influences ‘‘the ability to control the center of gravity (CoG) within and outside the base of support (BoS)’’ [2]. The coordination of internal forces, such as muscle and ligament forces, and the influence of external forces, such as gravity, impacts the ability to control momentum. Including momentum as a measure of dynamic stability should provide information about locomotor dynamics. Past studies of momentum generation have primarily focused on describing movement patterns during chair rise [14–16]. Recently, Kaya and colleagues investigated momentum control during chair rise and gait among healthy elders and elders with bilateral vestibular hypofunction [25]. These investigators suggested healthy elders limit the speed of rising from a chair and gait velocity to lessen momentum generation because of limits in balance control or strength which are needed to dissipate momentum generated by faster gait velocity [25]. The previous studies have not correlated dynamic stability measures such as momentum generation to specific muscle strength measures. The influence of specific muscles’ strength on dynamic stability, and on safe performance of these activities, deserves further investigation. Clinicians frequently suggest different movements to compensate for weakness. For example, during chair rise clinicians often advise the use of repeated forward trunk flexion, referred to as ‘rocking’, to build momentum to assist with lift-off during chair rise. A weaker individual may not be capable of safely controlling the momentum generation creating loss of dynamic stability and resulting in a failed chair rise,
11
stumbling forward or falling backward into the chair [19,25]. The continuous firing pattern of the quadriceps during chair rise has been reported [17]. Resisted exercise training can significantly improve quadriceps strength among elderly persons [11]. Therefore, we investigated the role quadriceps muscle strength plays in dynamic stability during chair rise and gait. We have focused on the influence of the upper body (encompassing the pelvis and all segments superior) during chair rise to include the most dynamic movements of body mass being translated and rotated over the fixed feet. The upper body demonstrates the greatest variation in movement patterns during chair rise [15,20]. Therefore, the use of upper body measurements could provide more comprehensive information on dynamic stability during chair rise. During gait we expected to see persons with weaker quadriceps strength compensate by implementing a larger range of momentum generation, to assist in the development of speed and movement. We hypothesized that quadriceps strength correlated: (1) inversely with chair rise cycle time, maximum trunk flexion, maximum range of lateral trunk flexion, upper body anteroposterior (A/P) linear momentum and whole body CoG to ankle A/P difference at lift-off during chair rise; (2) directly with chair rise maximum upper body vertical linear momentum; (3) directly with gait stride length, average velocity, and center of pressure (CoP)-CoG moment arm (defined in Section 2); and (4) inversely with gait double support time and range of whole body CoG lateral and A/P linear momentum.
2. Methods
2.1. Subjects Of 50 possible subjects, 34 participants met the inclusion/exclusion criteria. The subjects ranging in age from 60 to 88 years, were involved in the Strong-for-Life in-home, resistance strength training study [25]. All subjects provided written informed consent and Table 1 provides characteristic data of all the participants from our sample of convenience. To be selected each participant had to indicate that their health status limited their ability to perform one or more functional activities (Table 1), but be able to both follow commands and ambulate independently for 25 feet [26]. Each participant received medical approval from their primary care physician and each passed an in-home safetyexercise test which monitored heart rate, blood pressure, and respiratory rate during a series of exercises. Excluded were subjects with terminal illness, neurologic disease, diabetes mellitus, major loss of vision (legally blind), and painful or gross musculoskeletal
D. Moxley Scarborough et al. / Gait and Posture 10 (1999) 10–20
12
structural abnormalities (joint deformity such as in rheumatoid arthritis).
2.2. Instrumentation Strength measurements were performed at each subject’s home with a hand-held Nicholas MMT Dynamometer (Model c 01160; Lafayette Instrument). The total body biomechanical analysis was performed at the Massachusetts General Biomotion Laboratory. Kinematic and kinetic data acquisition is described in detail elsewhere [8,27,28]. The instrumentation included: two Kistler piezoelectric force plates, two computer terminals, four Selspot II™ optoelectronic
cameras; and 64 infrared light emitting diodes (irLEDs). The irLEDs are mounted on 11 plastic arrays attached securely to the following respective body segments of each participant: right and left feet, shanks, thighs and arms, pelvis trunk and head (Fig. 1). TRACK™, PVWAVE and SuperPlot II software were used for data collection, processing and analysis. Subjects performed the chair rise activity on an armless, backless, height adjustable chair [27]. The array position and orientation data were converted into body segment positions yielding 6 df for each of the 11 body segments and a three-dimensional android model (Fig. 4) [27]. The instrumentation and processing of raw kinematic data yields resolutions of B 1° and B1 mm
Table 1 List of subject characteristicsa Subject ID no.
Age (years)
Gender
Functional limitationb
Height (m)
Weight (kg)
Quadriceps MVIC strength (kg-Output/ kg-BW)
Leg tested
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 n= 34
65.42 80.00 75.75 75.66 68.92 82.83 64.83 70.08 81.66 66.16 75.42 88.08 67.92 68.75 85.92 65.58 67.16 80.33 72.50 68.16 77.83 66.00 88.42 83.50 70.25 79.00 65.41 67.42 81.50 79.20 73.66 73.58 60.25 72.17 x¯ = 73.80 (7.48)
F M F F M M F F F F M F F F M M F F M F M F F F F F F F F F F F F M F= 25, M= 9
c,f b,c,d,e a,b,e a,b,c a,b c a,b,c,e c,e a–i b–d,f,g,i c a–d,f a–e a–f c a–d,f,g a–f a,e a,c,f,g a,b e e a–f a–g,i a–i a–g,i a–e a–c,e–h b,c,e,f a–g a–g a,be–h c,d f
1.52 1.66 1.56 1.57 1.63 1.65 1.65 1.50 1.55 1.60 1.83 1.57 1.51 1.57 1.83 1.70 1.73 1.65 1.73 1.57 1.91 1.57 1.70 1.50 1.73 1.56 1.60 1.57 1.63 1.56 1.70 1.50 1.66 1.84 x¯ = 1.64 (0.11)
52.27 87.73 61.36 59.09 65.91 85.91 66.36 68.64 72.73 68.18 86.36 57.73 58.18 79.55 59.09 90.91 92.27 75.00 59.09 47.73 79.55 77.27 69.09 54.09 67.27 63.64 55.91 102.73 63.64 56.36 93.18 77.27 84.09 84.09 x¯ =26.67 (4.99)
8.70 (0.00) 8.29 (0.15) 8.37 (0.52) 10.19 (0.16) 11.76 (0.05) 7.91 (0.26) 17.23 (1.21) 5.73 (0.14) 9.81 (0.35) 10.27 (0.38) 6.82 (0.63) 11.06 (0.72) 10.51 (0.17) 10.71 (0.20) 11.92 (1.41) 5.8 (0.21) 4.66 (0.38) 13.97 (1.93) 15.15 (1.41) 8.33 (0.34) 13.31 (0.65) 4.12 (0.17) 5.53 (0.56) 5.88 (0.48) 4.90 (0.14) 7.14 (0.00) 13.86 (0.40) 7.10 (0.09) 6.5 (0.51) 12.46 (0.74) 3.68 (0.60) 0.54 (0.07) 5.35 (0.08) 11.38 (0.88) x¯ =8.79 (3.71)
R R L R R R R R R R R R R R L R R R R R R R R L R R R R R R R L R R R =30, L= 4
a
Standard deviations in parentheses. List of functional limitations, based on health status, include subject responding as either ‘limited a little’ or ‘limited a lot’ to one or more of the following: (a) moderate activities, such as moving a table, pushing a vacuum cleaner, bowling or playing golf; (b) lifting or carrying groceries; (c) climbing several flights of stairs; (d) climbing one flight of stairs; (e) bending, kneeling or stooping; (f) walking more than a mile; (g) walking several blocks; (h) walking one block; (i) bathing or dressing yourself. b
D. Moxley Scarborough et al. / Gait and Posture 10 (1999) 10–20
Fig. 1. Subject with testing arrays in chair rise test position.
[27,28]. Upper body (head, arms, trunk and pelvis) and whole body linear momentum values were calculated as the product of each segment’s mass times the segment’s CoG velocity (momentum=mass times velocity, kgM/ s)] [8]. Segmental mass estimations and kinematic data are used to calculate the CoG of each segment and all segments are used to calculate whole body CoG [27]. Kinetic data including vertical reaction forces, and center of pressure (CoP) were measured from the force plates [27].
2.3. Protocol Subjects’ muscle strength was assessed at each participant’s home within 2 weeks prior to the Biomotion Laboratory tests. Quadriceps muscle strength was measured by a single tester. Strength was defined as the force generated during a maximum voluntary isometric contraction (MVIC) measured in kilograms (kg) with a hand held dynamometer during a 3-s isometric hold at 60° knee flexion; the participant was seated in a chair with feet on the floor [26]. The dynamometer was calibrated at 90.50 kg prior to each test and was placed against the right shin two finger widths (about 5 cm) above the malleoli. The subject was asked to ‘‘push
13
as hard as you can into me’’. The right knee was chosen for consistency across subjects; however, left knee measurements were collected from four subjects, who were fearful of potential right knee pain during quadriceps muscle strength testing. An initial practice measurement was performed followed by two recorded strength measurements. The two recorded MVIC values were each divided by the individual’s weight [29]. The average of the two values was used in the statistical analysis. All participants were barefoot during chair rise and gait tests. For each chair rise trial the participant was seated with the greater trochanters approximately 4 cm from the front edge of a backless chair, adjusted to 100% knee height, measured as the distance from the right medial tibial plateau to the floor. Each subject performed one practice and two recorded trials. Each participant placed their feet as requested in a self constrained position, 10 cm apart, with 18° of ankle dorsi flexion. Trials were considered successful when participants kept their arms folded in a constrained position in front of their abdomen and their feet remained still during the chair rise. Each participant was asked to arise from the chair as they ‘normally do’ beginning on ‘go’ after the cue ‘one, two, ready, go’. Data collection began on ‘ready’ and once the subject stood upright, s/he looked straight ahead and stood as still as possible during the remaining portion of the total 7-s data collection period. Arm and foot position constraints were used to improve the consistency of the body position during chair rise testings [14,18]. A total of 29 subjects were able to arise independently, without taking a step or unfolding their arms, at 100% knee height, but five subjects were unable to arise from the 100% knee height chair without using their arms to push up or assistance from the tester; they repeated the same protocol with a 120% knee height chair. The variables chosen to measure dynamic postural stability during chair rise were analyzed only for subjects able to perform chair rise at 100% knee height. From start of movement (SOM) to end of rise (EOR) we analyzed maximum upper body vertical and anteroposterior linear momentum, maximum trunk flexion (measured relative to room coordinates) and maximum range of lateral trunk flexion. These measures were collected between the SOM time and EOR time of chair rise as defined in Fig. 2. The chair rise cycle time was also calculated for all subjects as the time from SOM through EOR. The A/P difference between the CoG and the ankle joint (the average of the left and right ankle joint centers’ positions) in the sagittal plane at the time of lift-off from the chair was normalized to the A/P difference of CoG to ankle joint at the end of rise for each individual. This value was then normalized to each individual’s height in meters. For each gait trial the subject walked approximately 8 m. Data collection began when each subject entered
D. Moxley Scarborough et al. / Gait and Posture 10 (1999) 10–20
14
whole body CoG anteroposterior (A/P) linear momentum (the absolute difference between the maximum and minimum anteroposterior linear momentum values during a gait cycle), and range of whole body CoG lateral linear momentum (the absolute difference of the maximum right and left lateral momentum values, during a gait cycle).
2.4. Data analysis The average value for all data from two trials was analyzed. Means, standard deviations, and linear correlation analyses were performed for all data. Pearson product-moment correlations between quadriceps strength and all the dynamic stability variables for chair rise and gait were performed to test each hypothesis. For analysis of group differences between chair rise strategy groups to be more conservative an ANOVA (two-tailed) was performed. Statistical significance of correlations and group differences was determined at PB 0.05. Fig. 2. The determination of chair rise events. (A) Start of movement (SOM), defined as the time at which forward upper body momentum begins (vertical line labeled ‘S’). (B) Lift-off (LO), defined as the time at which the thigh segment moves upwards from its original position by 2° (vertical line labeled ‘L’). (C) End of rise (EOR), defined as the time at which the upper body CoG reaches its highest vertical position (vertical line labeled ‘E’).
the 2 × 2 ×2-m viewing volume, approximately 3 m beyond the starting point. Each subject was asked to ‘‘move forward in as straight a line as possible, walking at your normal pace, as if you were taking a brisk walk in the park’’. The following gait variables were determined: stride length (distance traveled between consecutive ipsilateral heel strikes), gait velocity (average whole body CoG velocity during one gait cycle), double support time (one of the two periods of time during which the body is supported by both limbs, expressed as % of the gait cycle), maximum moment arm (the distance between the whole body CoG and CoP, in both the anteroposterior and medial lateral planes during single limb stance phase) [17], range of Table 2 Normalized quadriceps muscle strengtha values Subjects
n
Mean
S.D.
Range
Performed CR at 100% knee height Performed CR at 120% knee height Unable to perform CR
29
9.58
3.33
4.12–17.23
4
5.18
1.26
3.68–5.88
1
0.54
a
Strength equals the total output of knee extension strength in kg divided by total body weight in kg (kg-output/kg-BW). CR, chair rise.
3. Results
3.1. Quadriceps muscle strength The weight adjusted quadriceps strength for all subjects ranged from 0.54 to 17.23 kg per kg of body weight (Table 2).
3.2. Relationship of quadriceps muscle strength to measures of dynamic stability during chair rise Quadriceps strength had a significant, moderately strong correlation with maximum upper body vertical linear momentum, (r=0.53, PB 0.005) and there also was a significant direct correlation with maximum upper body anteroposterior (A/P) linear momentum, (r= 0.38, PB0.05), (Fig. 3). Fig. 3C demonstrates that as the strength of the quadriceps muscle increased, the faster each subject could arise from the chair. There was a significant inverse correlation between quadriceps muscle strength and chair rise cycle time (r= − 0.48 and PB 0.05). The participant with the least quadriceps muscle strength (0.54 kg, S.D.= 0.07) was unable to perform chair rise at either 100% or the increased seat height of 120% of knee height. There were four other elders with low values of knee extensor strength who were unable to perform chair rise with the seat of the chair at 100% of knee height but could arise from the chair with the seat at 120% of knee height. The whole body CoG to ankle A/P difference at lift-off did not correlate with quadriceps strength (r= − 0.07, P= 0.37).
D. Moxley Scarborough et al. / Gait and Posture 10 (1999) 10–20
15
3.3. Mo6ement strategies of chair rise During chair rise subjects used three major movement patterns, or strategies. The most frequently observed was the momentum-transfer chair rise strategy (Fig. 4) first described by Schenkman and colleagues [15,16]. Elders in our study also performed the exaggerated trunk flexion chair rise strategy (Fig. 5), described previously and referred to as the stabilization strategy by Hughes and Schenkman [15]. The third strategy we observed has not previously been reported. The dominant vertical chair rise strategy is described in detail in Fig. 6. The subjects in this sample consistently performed the same strategy for each of the consecutive two chair rise trials. Table 4 presents descriptive findings of average quadriceps strength values and subject characteristics for each of the three chair rise strategy groups. There was no statistically significant differences in quadriceps strength across groups, P= 0.99.
3.4. Relationship of quadriceps strength to dynamic stability during gait
Fig. 3. Relationships between relative quadriceps muscle strength (kg-Output/kg-BW) and dynamic stability during chair rise. (A) The linear relationship between relative quadriceps muscle strength and maximum upper body vertical linear momentum during chair rise (r = 0.53, P B 0.005). (B) The linear relationship between relative quadriceps muscle strength and maximum upper body A/P linear momentum (r= 0.38, P B0.05). (C) The linear relationship between quadriceps muscle strength and chair rise cycle time (r = −0.48, P B0.01). The bold lines represent the regression lines and the dashed lines show the 95% confidence interval ranges (n= 29).
Trunk motion during chair rise was not significantly related to knee extensor strength. Quadriceps muscle strength was not correlated with either maximum trunk flexion (r= − 0.13, P = 0.4874) or range of lateral trunk flexion, (r= − 0.097, P =0.6165). Table 3 summarizes the correlations of the measures of dynamic stability during chair rise.
As hypothesized, quadriceps strength had a significant, moderately high correlation with stride length (r=0.558, PB 0.001) and preferred gait velocity (r= 0.51, PB0.002) (Fig. 7). Double support time correlated inversely with quadriceps strength (r= −0.41, PB 0.02). Maximum moment arm had a lower but positive correlation with quadriceps muscle strength (r=0.35, PB 0.05). The range of the whole body CoG A/P linear momentum values correlated directly with quadriceps strength (r= 0.47, P= 0.004, n= 31). There was no statistical correlation between quadriceps strength and maximum range of whole body lateral linear momentum (r= 0.25, P=0.08, n= 33). Table 5 summarizes the correlations among the measures of dynamic stability during gait.
3.5. Effect of age on quadriceps strength and measures of dynamic stability during chair rise and gait Age did not predict quadriceps muscle strength (r= 0.0843, P= 0.6638). Of the 34 subjects examined, 19 were young elderly (60–75 years) and 15 were old elderly ( \ 75.1 years). The subject who was unable to perform chair rise at 100 or 120% knee height was in the young elderly group. Of the persons requiring the increased 120% knee height chair, half were in the young elderly group and the other half in the old elderly group. Of the persons who were able to successfully arise from a chair at 100% knee height, 16 were in the young elderly and 13 were in the old elderly age groups. Age did not correlate significantly with measures of dynamic stability during gait or chair rise.
16
D. Moxley Scarborough et al. / Gait and Posture 10 (1999) 10–20
Table 3 Linear correlations of dynamic stability measures during chair rise
Upper body A/P linear momentum Upper body vertical linear momentum Chair rise cycle time Maximum trunk flexion
Upper body vertical Chair rise linear momentum cycle time
Maximum trunk flexion
Range of lateral trunk flexion
CoG to ankle A/P difference
r=0.67, P= 0.0001* r = −0.28, P= 0.074
r = 0.37, P =0.03* r=−0.01, P =0.48 r =0.08, P =0.34
r= −0.71, P =0.0001* r=−0.04, P=0.42 r =−0.14, P = 0.22 r=−0.02, P =0.46 r = 0.42, P =0.01* r= 0.25, P = 0.09 r =0.29, P= 0.13
r =−0.02, P = 0.45 r=−0.14, P =0.23
* Correlation reaches level of significance.
4. Discussion Development of effective strengthening treatment programs for prevention of falls and maintaining safe, independent function among elderly persons depends on determination of how specific muscle strength influences dynamic stability during the common activities of arising from a chair and walking. We focused on the quadriceps femoris muscle strength because of its large size, ease of testing and known association of power generation during chair rise [10,11,15,17,21]. The detailed biomechanical analysis of several dynamic stability measures allowed us to discover the important role quadriceps muscle strength plays in dynamic stability during chair rise and during gait among elderly persons. Contrary to clinical wisdom and our hypothesis, during chair rise our elderly subjects used momentum differently than expected, demonstrating three strategies to accomplish chair rise, independent of quadriceps muscle strength (Table 4). During chair rise some elders avoid the potentially destabilizing, but more functional, momentum transfer strategy, apparently because they lack the coordination and/or strength in muscle groups other than the quadriceps needed to dampen and control the increased forces induced by the rapid movement resulting from momentum generation. However, persons with the greatest quadriceps strength values typically performed chair rise faster and generated greater vertical and A/P linear momentum, demonstrating better stability and ability to control movement, regardless of which chair rise strategy they performed. These findings suggest that clinicians caring for elderly persons should monitor quadriceps strength and recommend quadriceps strengthening exercises for maintaining and improving dynamic stability. Having normal quadriceps strength is important in maintaining dynamic stability during the common activity of arising from a chair. Schenkman and colleagues described four phases of chair rise during two strategies of chair rise [14,15,18]. The momentum-transfer chair rise strategy was observed in healthy/normal subjects and the stabilization strategy was observed in
functionally impaired elderly subjects [14,15,18]. Investigators established the importance of quadriceps strength for successful chair rise, especially from low chair heights, among healthy adults and functionally impaired elders [9,22].
Fig. 4. Momentum-transfer chair rise strategy. At time of lift-off, the upper body anterior momentum transfers to total body vertical momentum with continued anterior momentum [16,17]. The following is our kinematic description of the momentum-transfer strategy, to assist the clinician when observing persons: at the time of lift-off upper body flexion continues with initiation of knee extension which smoothly transitions to simultaneous back and knee extension, until erect posture is attained. (The vertically directed line originating from the force plates within the floor represents the ground reaction force. The cross seen at the level of the pelvis represents the whole body CoG.)
Fig. 5. Exaggerated trunk flexion chair rise strategy. The exaggerated trunk flexion chair rise strategy has been described previously and referred to as the stabilization strategy [8,17]. We have expanded the description as: exaggerated trunk flexion prior to lift-off, frequently followed by further trunk flexion, placing the CoG over the feet resulting in delayed trunk extension during the final transition to the erect posture. (The vertically directed line originating from the force plates within the floor represents the ground reaction force. The cross seen at the level of the pelvis represents the whole body CoG.)
D. Moxley Scarborough et al. / Gait and Posture 10 (1999) 10–20
Fig. 6. Dominant vertical rise chair rise strategy. The dominant vertical chair rise strategy is described as follows: at time of lift-off, upper body anterior momentum lessens and cessation of forward trunk flexion immediately follows with subsequent dominance of vertical momentum and knee extension. (The vertically directed line originating from the force plates within the floor represents the ground reaction force. The cross seen at the level of the pelvis represents the whole body CoG.)
We found a strong correlation between quadriceps muscle strength and maximum upper body vertical linear momentum during chair rise. Quadriceps muscle contraction creates the necessary vertical velocity, which in turn determines the vertical linear momentum of each person as they arise from a chair. We also found quadriceps muscle strength correlated inversely with chair rise cycle time. These observations confirm and extend previous conclusions, that the time required to arise from a chair provides a good indirect measurement of knee extensor strength [10,11]. In contrast to our original hypothesis, lateral trunk flexion during chair rise does not correlate with quadriceps muscle strength. We hypothesized that persons with stronger quadriceps would demonstrate greater dynamic stability and thus have less lateral instability. Persons with weak quadriceps muscles may also have weakness in lateral and other proximal stabilizing muscles, potentially leading to lateral instability. However, the predominant anteroposterior (A/P) direction of movement that occurs during chair rise leads to instability primarily in the same A/P direction, not to lateral
17
instability [19]. Future investigations such as the relationships of lateral trunk flexion and lateral center of gravity displacement during chair rise to the strength of the hip abductors and ankle everters, may help to establish if these muscles, in addition to the quadriceps femoris, have a primary role in dynamic stability during chair rise. We also hypothesized that the weaker elderly participants would generate greater A/P momentum to assist with lift-off, to compensate for their decreased strength. Instead, quadriceps muscle strength correlated directly with maximum upper body A/P linear momentum. There are at least two explanations for this unexpected finding. First, stronger persons are better able to generate a greater velocity on arising, thus creating higher momentum. Second, and more interestingly, the weaker elders, in general, do not attempt to generate greater A/P momentum as a compensatory strategy. This is probably because they lack the strength to control increased forces. We had expected, as suggested by previous investigators, that weaker participants would increase trunk flexion prior to lift-off in order to position their CoG over their ankles and to generate momentum [14,18]. The exaggerated trunk flexion strategy was performed by several participants in our investigation, however, their quadriceps muscle strength ranged from low to high values. Some of the elderly participants in our study used the dominant vertical chair rise strategy, and these elderly individuals also have values of quadriceps muscle strength ranging from low to high values. Surprisingly, certain weaker elderly participants use this strategy, despite the increased leg muscle effort required and the apparent energetic inefficiency of this movement strategy to arise from a chair. Several investigators have suggested that the whole body CoG to ankle position A/P difference at lift-off varies with the movement strategies of chair rise [3,15]. We did not find a statistically significant correlation between quadriceps strength and whole body CoG to ankle position A/P difference
Table 4 Chair rise strategy groups with respective quadriceps strength values and subject characteristics
Momentum transfer strategy
Exaggerated flexion strategy
Dominant vertical rise strategy
Mean (S.D.) Range Mean (S.D.) Range Mean (S.D.) Range
n
Quadriceps strengtha
Age (years)
Height (m)
Weight (kg)
17
9.62 (3.59) 5.35–17.23 9.71 (3.74) 4.90–13.31 9.42 (2.99) 4.12–13.97
72.63 (8.58) 60.25–88.42 74.86 (8.97) 65.42–85.92 74.47 (5.34) 66.00–81.66
1.61 (0.067) 1.50–1.73 1.75 (0.165) 1.52–1.91 1.64 (0.121) 1.55–1.84
69.89 (15.08) 47.73–102.73 64.55 (11.73) 52.27–79.55 74.43 (9.85) 59.09–86.36
4
8
a Quadriceps muscle strength values [(kg-output/kg-BW)100]. There was no statistical difference in quadriceps strength between chair rise strategy groups (ANOVA, P=0.958).
18
D. Moxley Scarborough et al. / Gait and Posture 10 (1999) 10–20
Fig. 7. Relationships between relative quadriceps muscle strength (kg-Output/kg-BW) and dynamic stability during gait. (A) Relationship between relative quadriceps muscle strength and stride length (r= 0.56, P = 0.001, n = 34). (B) Relationship between relative quadriceps muscle strength and gait velocity (r = 0.51, P= 0.002, n =34). (C) Relationship between relative quadriceps muscle strength and the maximum range of whole body A/P linear momentum (r= 0.47, P =0.004, n = 31). The bold lines represent the linear regression lines and the dashed lines show the 95% confidence interval ranges.
at lift-off. These data suggest that quadriceps femoris muscle strength alone does not determine the strategy for arising from a chair in functionally limited elderly persons. The reasons accounting for the different strategies used to arise from a chair in our study group require further investigation. Participants who are unable to arise from a chair at 100% of their knee height have failed in their attempt while using one of the above
three strategies. Stepping forward, backwards or falling back onto the seat (sit-back) are body reaction movements, that we have observed during failed attempts at arising from the chair [19]. These adjustments for positioning the body can sometimes lead to falls and injuries [1,19]. Continued investigations to determine which strategy provides the least likelihood of failure in arising from a chair among elderly persons with all ranges of quadriceps strength may be valuable to the clinician for designing preventative health programs for functionally limited, weaker, at-risk individuals. At present clinicians may instruct elderly persons to use greater momentum, or ‘rocking’, to assist in their liftoff during chair rise. The biomechanical analysis performed in our study suggests using great caution in offering this advise as it may inadvertently induce a person with weak quadriceps muscles to fall forward if the elder cannot control the increased momentum associated with this pattern of movement [19]. Muscle strength and motor control are also needed to dampen the effects of this additional generated momentum. Our data suggest that coordinated anteroposterior, then vertical momentum peaks are needed to successfully arise from a chair (Figs. 4–6). Our investigation further supports the importance of quadriceps strength to dynamic stability during gait. As hypothesized, stride length, gait velocity, and maximum moment arm correlated directly and double support time correlated inversely with quadriceps muscle strength. Similar findings from a previous investigation of 26 elderly persons demonstrated that quadriceps strength correlated significantly with step length (r= 0.69 PB 0.001) [21]. Our data also supported previous findings from larger sample sizes that stride length correlates directly with gait velocity [12,24]. Longer stride length obviates shuffling; shuffling is observed frequently in older persons and may also decrease falls which often occur during hurried gait or when turning in older individuals [1,30]. Creating longer strides allows a person to increase gait speed, which is important for independence. The ability of an elderly person to increase their walking speed to avoid a moving obstacle on the sidewalk (such as a person on roller skates, a dog, or a bicyclist etc.) or to cross a road quickly is an important safety issue among independent, community dwelling, elderly, persons. Our data indicate that elderly persons with greater quadriceps muscle strength had shorter double support time than weaker individuals. Double support time has been used as a parameter of dynamic stability by many investigators [2,7,23,24]. Elders with greater quadriceps strength values had larger maximum moment arm values during gait. Therefore, stronger elderly participants move their CoG farther away from their BoS, than the weaker participants. This demonstrates confidence in controlling the CoG beyond the BoS ‘comfort zone’
D. Moxley Scarborough et al. / Gait and Posture 10 (1999) 10–20
19
Table 5 Linear correlations of dynamic stability measures during gait
Stride length Gait velocity
Gait velocity
Double support time
Moment arm
Range of A/P momentum
Range of lateral momentum
r = 0.94, (n=34) P =0.0001*
r = −0.69, (n= 34) P= 0.0001* r= −0.70, (n= 34) P = 0.0001*
r = 0.82, (n =34) P = 0.0001* r= 0.80, (n =34) P= 0.0001* r=−0.44, (n = 34) P= 0.0099*
r = 0.14, (n = 34) P= 0.25 r =−0.05, (n =27) P= 0.41 r =−0.13, (n =27) P =0.26 r =−0.21, (n = 31) P= 0.13
r= 0.36, (n =34) P= 0.03* r =0.17, (n =29) P=0.19 r =−0.09, (n =29) P=0.32 r =0.24, (n = 33) P =0.09 r =0.20, (n =31) P=0.14
Double support time Maximum Moment arm Range of A/P momentum * Correlation reaches level of significance.
which is a primary skill required in dynamic stability. The relationship of quadriceps strength to maximum range of A/P linear momentum values during gait suggests greater quadriceps strength allows elderly persons the ability to generate greater forward momentum likely contributing to increased gait velocity. Persons with weaker quadriceps strength values did not develop high momentum values as a strategy to increase gait velocity, suggesting inability to control the additional forces that result from greater momentum generation. In activities such as walking, it appears that greater quadriceps muscle strength enhances dynamic stability and may play an important role in reducing the risk of falls and related injuries in functionally limited elderly individuals. Limitations of the present investigation include a modest sample size and a predominance of female participants. Strength measured in Newtons of force, as opposed to our kilogram units, might allow more direct comparison to results of other investigations that use force units. This study implemented a standardized, scientifically accepted isometric strength testing protocol, which has been used when correlating strength to functional tasks [26,29,31]. Further investigations of the correlations between quadriceps muscle strength and the strength of other muscles, such as the trunk extensors, the abdominal muscles, hip flexors, abductors and extensors, ankle plantar flexors, dorsi flexors, inverters and everters and measurements of dynamic stability during chair rise and gait should be carried out in a larger sample of functionally limited elders. The influence of exercise training, specifically quadriceps femoris muscle strengthening, on different measurements of dynamic stability among elderly individuals and the effects of such training on the frequency of falls and injuries, needs to be assessed. Nonetheless, our data represent the largest sample and most sophisticated analysis reported to date evaluating the relationship between strength and a variety of dynamic stability measurements during chair rise and gait.
5. Conclusions With these elders, increased generation of A/P momentum was not used as a compensatory strategy for weak quadriceps strength during chair rise or gait. The results of our investigation introduces clinical perspectives on three different movement strategies to accomplish chair rise among elders and the relationship of quadriceps strength to dynamic stability measures. Knee extensor strength correlates with most measures of dynamic stability during chair rise and gait. Our data indicate that clinicians should not suggest that patients use compensatory momentum inducing locomotor strategies unless the patient has sufficient strength to control these induced forces. Adequate quadriceps muscle strength is essential for the ability to successfully perform functional activities of arising from a chair and walking, as importantly, quadriceps strength enhances the generation and control of momentum and maintenance of good dynamic stability, ultimately influencing safety and the likelihood of falls, during these two locomotor activities of daily living.
Acknowledgements This research was supported by grants from the National Institutes of Health (R01AG12561 and P50 AG11669-03). We are grateful for the cooperation and assistance of New England Research Institute’s staff from its Roybal Center’s Strong for Life exercise project, and for the assistance from Massachusetts General Hospital Biomotion Laboratory staff, in particular Jose V. Ramirez, MD, for his edits and locomotor data collection. Acknowledgment and appreciation is extended to Patrick O. Riley, Ph.D. for his assistance during the initial phases of this research. An extended appreciation, from the first author, goes to my father, Richard T. Moxley III, MD for his dedication, guidance, research skills and encouragement.
20
D. Moxley Scarborough et al. / Gait and Posture 10 (1999) 10–20
References [1] Tinetti ME, Speechley M, Ginter SF. Risk factors for falls among elderly persons living in the community. N Engl J Med 1988;319:1701– 7. [2] Krebs DE, Lockert J. Vestibulopathy and gait. In: Spivach BS, editor. Evaluation and management of gait disorders. New York: Marcel Dekker, 1995:93–115. [3] Pai Y-C, Patton J. Center of mass velocity—position predictions for balance control. J Biomech 1997;30:347–54. [4] Horak FB, Shupert CL, Mirka A. Components of postural dyscontrol in the elderly: a review. Neurobiol Aging 1989;10:727 – 38. [5] Lord SR, Clark RD, Webster IW. Postural stability and associated physiological factors in a population of aged persons. J Gerontol Med Sci 1991;46:69–76. [6] Buchner DM, de Lateur BJ. The importance of skeletal muscle strength to physical function in older adults. J Behav Med 1991;13:91 – 7. [7] Wolfson L, Whipple R, Amerman P, Tobin J. Gait assessment in the elderly: a gait abnormality rating scale and its relation to falls. J Gerontol Med Sci 1990;45:M12–9. [8] Hutchinson EB, Riley PO, Krebs DE. A dynamic analysis of the joint forces and torques during rising from a chair. IEEE Trans Rehab Engin 1994;2:49–56. [9] Hughes MA, Myers BS, Schenkman ML. The role of strength in rising from a chair in the functionally impaired elderly. J Biomech 1996;29:1509–13. [10] Bohannon RW, Smith J, Hull D, Palmeri D, et al. Deficits in lower extremity muscle and gait performance among renal transplant candidates. Arch Phys Med Rehabil 1995;76:547–51. [11] Fiatarone MA, Marks EC, Ryan ND, Meredith CN, et al. High-intensity strength training in nonagenarians: effects on skeletal muscle. J Am Med Assoc 1990;263:3029–34. [12] Perry J, Mulroy SJ, Renwick SE. The relationship of lower extremity strength and gait parameters in patients with post-polio syndrome. Arch Phys Med Rehabil 1993;74:165–9. [13] Schultz AB, Alexander NB, Ashton-Miller JA. Biomechanical analyses of rising from a chair. J Biomech 1992;25:1383– 91. [14] Schenkman M, Berger RA, Riley PO, Mann RW, et al. Wholebody movements during rising to standing from sitting. Phys Ther 1990;70:638 – 48.
.
[15] Hughes MA, Schenkman ML. Chair rise strategy in the functionally impaired elderly. J Rehabil Res Dev 1996;33:409–12. [16] Pai Y-C, Naughton BJ, Chang RW, Rogers MW. Control of body centre of mass momentum during sit-to-stand among young and elderly adults. Gait Posture 1994;2:109 – 16. [17] Millington PJ, Myklebust BM, Shambes GM. Biomechanical analysis of the sit-to-stand motion in elderly persons. Arch Phys Med Rehabil 1992;73:609 – 17. [18] Ikeda ER, Schenkman ML, Riley PO, Hodge WA. Influence of age on dynamics of rising from a chair. Phys Ther 1991;71:473– 81. [19] Riley PO, Krebs DE, Popat R. Biomechanical analysis of failed sit to stand. IEEE Trans Rehab Engin 1997;5:353 – 9. [20] Schenkman M, Hughes MA, Samsa G, Studenski S. The relative importance of strength and balance in chair rise by functionally impaired older individuals. J Am Geriatr Soc 1996;44:1441–6. [21] Judge JO, Davis RB, Ounpuu S. Step length reductions in advanced age: the role of ankle and hip kinetics. J Gerontol Med Sci 1996;51A:303 – 12. [22] Imms FJ, Edholm OG. Studies of gait and mobility in the elderly. Age Ageing 1981;10:147 – 56. [23] Gill-Body KM, Krebs DE. Locomotor stability problems associated with vestibulopathy: assessment and treatment. Phys Ther Practice 1994;13:232 – 45. [24] Perry J. Gait analysis: normal and pathological function. Thorofare, NJ: SLACK, 1992:19 – 47 also pp. 287 – 97. [25] Kaya BK, Krebs DE, Riley PO. Dynamic stability in elders: momentum control in locomotor ADL. J Gerontol Med Sci 1998;53A:M126– 34. [26] Jette AM, Lachman M, Giorgetti MM, Assmann SF, et al. Exercise: it’s never too late!. Am J Public Health 1998;89:66–72. [27] Riley PO, Mann RW, Hodge WA. Modelling of the biomechanics of posture and balance. J Biomech 1990;23:503 – 6. [28] Antonsson EK, Mann RW. Automatic 6-D.O.F. kinematic trajectory acquisition and analysis. J Dyn Syst Meas Control 1989;111:31 – 9. [29] Andrews AW, Bohannon RW. Normative values for isometric muscle force measurements obtained with hand-held dynamometers. Phys Ther 1996;76:248 – 59. [30] Alexander NB. Gait disorders in older adults. J Am Geriatr Soc 1996;44:434 – 51. [31] Krebs DE, Jette AM, Assmann SF. Moderate exercise improves gait stability in disabled elders. Arch Phys Med Rehabil 1998;79:1489 – 95.