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Effects of age and step length on joint kinetics during stepping task
Journal of Biomechanics 48 (2015) 1679–1686
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Effects of age and step length on joint kinetics during stepping task Kathleen A. Bieryla a,n, Christine Buffinton b a b
Biomedical Engineering Department, Bucknell University, One Dent Drive, Lewisburg, PA 17837, USA Mechanical Engineering Department, Bucknell University, One Dent Drive, Lewisburg, PA 17837, USA
art ic l e i nf o
a b s t r a c t
Article history: Accepted 30 May 2015
Following a balance perturbation, a stepping response is commonly used to regain support, and the distance of the recovery step can vary. To date, no other studies have examined joint kinetics in young and old adults during increasing step distances, when participants are required to bring their rear foot forward. Therefore, the purpose of this study was to examine age-related differences in joint kinetics with increasing step distance. Twenty young and 20 old adults completed the study. Participants completed a step starting from double support, at an initial distance equal to the individual's average step length. The distance was increased by 10% body height until an unsuccessful attempt. A one-way, repeated measures ANOVA was used to determine the effects of age on joint kinetics during the maximum step distance. A two-way, repeated measures, mixed model ANOVA was used to determine the effects of age, step distance, and their interaction on joint kinetics during the first three step distances for all participants. Young adults completed a significantly longer step than old adults. During the maximum step, in general, kinetic measures were greater in the young than in the old. As step distance increased, all but one kinetic measure increased for both young and old adults. This study has shown the ability to discriminate between young and old adults, and could potentially be used in the future to distinguish between fallers and non-fallers. & 2015 Elsevier Ltd. All rights reserved.
Keywords: Step length Old adults Kinetics
1. Introduction Following a balance perturbation, one or more steps are commonly used to regain support. A number of studies have used a forward lean and release protocol to instigate a balance perturbation, simulating a fall (Hsiao-Wecksler and Robinovitch, 2007; Madigan and Lloyd, 2005). Participants lean forward while in a harness and are released with instructions to recover by taking one step, though some studies have focused on comparing multiple steppers to single steppers (Carty et al., 2011, 2012). Instructing participants to limit (or not limit) the number of steps during forward lean recovery was shown to have no effect on lower extremity peak joint torques (Cyr and Smeesters, 2007). Studies show young adults can recover from larger lean angles than old (Madigan and Lloyd, 2005; Thelen et al., 1997; Wojcik et al., 1999). Most of the forward lean and release studies focused on kinematics and kinetics from release to heel contact. One study examined joint kinetics during the support phase of the forward lean protocol, from heel contact to steady state, and found old adults had trends towards larger peak extensor torques at the hip and ankle and significantly lower peak knee extensor torques compared to young adults, indicating different phases of recovery n
Corresponding author. Tel.: þ 1 570 577 2341; fax: þ 1 570 577 3659. E-mail address: [email protected] (K.A. Bieryla).
http://dx.doi.org/10.1016/j.jbiomech.2015.05.028 0021-9290/& 2015 Elsevier Ltd. All rights reserved.
have different joint torque requirements (Madigan and Lloyd, 2005). Additionally, maximum recovery lean magnitude as a percent of body weight and the number of steps to recover from a forward lean at 25% body weight was found to be a predictor of future falls (Carty et al., 2015). These studies provide valuable information, but can also be time consuming and require specialized equipment. The maximum step length (MSL) test has been used as a clinical assessment of balance (Cho et al., 2004; Nnodim et al., 2006). The MSL test requires a person to step out with one leg as far as possible, and then return to the starting position (Medell and Alexander, 2000). The MSL is shorter in old adults compared to young (Medell and Alexander, 2000; Schulz et al., 2008) and hip and knee kinetics were greater for young women compared to old women during MSL (Schulz et al., 2008). During the forward MSL test (step out and back), peak torques occurred during the “push back” phase (stepping back) (Schulz et al., 2007). This may be one reason the authors explored a variation of the MSL, “back only”, where participants started with their feet separated in double support, then returned both feet together by taking a backward step. When participants were instructed to rank the difficulty of the various versions of the MSL, the majority of the participants qualitatively rated the “back only” version of the MSL as the most difficult (Schulz et al., 2007). Both versions of the MSL test require less time to set up than the forward lean protocol as there is no specialized equipment required to place participants into the initial starting position.
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This study explored a movement similar to the MSL “back only” version in that the starting position is also double support. However, in the current study, the participant steps forward, bringing the back foot alongside the front foot, completing the step. As the back stepping movement is less likely during recovery from a fall, the forward stepping movement was examined as a more natural motion after a balance recovery step. This is an important extension to balance-perturbation tests such as the forward lean and release, since adults must also be able to re-initiate forward motion after a balance recovery step(s), and the inability to do so may be another cause of loss of balance. The static starting position isolates a worst-case scenario, when a person does not have momentum to continue forward motion with a second step. To date, no other studies have compared joint kinetics in young and old adults during increasing step distances, starting in double support and completing the step. Therefore the purpose of this study was twofold: to examine age-related differences in the maximum step distance participants are able to complete, and to examine age-related differences in joint kinetics with increasing step distance. It was hypothesized that (1) young adults are able to successfully complete longer step distances than old adults, (2) peak joint kinetics will increase for both groups as step distance increases, and (3) young adults will have larger peak joint kinetics than old adults during their maximum step distance.
2. Methods Twenty young (10 male, 10 female) and 20 old (10 male, 10 female), healthy adults were recruited from the local community to complete the study (Table 1). The study was approved by Bucknell University's Institutional Review Board and written consent was obtained. The study consisted of participants beginning in double support at an initial distance equal to the individual's average step length, and stepping forward with the back foot to bring it alongside the front foot. The distance between the front heel and back heel was increased by 10% of body height (BH) until the participant was unable to complete the step successfully. To determine step length, reflective markers were placed on the right and left heel of the participant. They were then instructed to walk normally in a straight line across the room. After a minimum of three passes, data was recorded using a Vicon Motion Analysis T-10 Series System (Motion Systems Ltd., Centennial, CO, USA). Average step length was calculated from a minimum of three recorded step lengths. The study began with the participant's dominant foot on the front force plate and non-dominant foot on the back force plate (Fig. 1). Dominance was determined by asking the participants with which foot they would kick a soccer ball. Participants were barefoot and instructed to stand relaxed with arms across their chest and look straight ahead. When signaled, they stepped forward, ending with both feet on the front force plate, with heels on a target line. Three trials were attempted with the dominant leg forward followed by three trials with the non-dominant leg forward. Upon successful completion of two out of the three trials, Table 1 Participant characteristics by age group and gender. Mean (standard deviation) reported for age, height, and mass.
Young female (n¼ 10) Young male (n¼ 10) Old female (n¼ 10) Old male (n¼ 10)
Age (yr)
Height (m)
Mass (kg)
20.3 19.6 73.8 77.4
1.64 1.80 1.60 1.74
65.1 76.1 64.7 80.0
(2.0) (1.5) (3.5) (5.6)
(0.08) (0.08) (0.04) (0.06)
(16.7) (11.5) (10.4) (13.0)
Fig. 1. Double support starting position for the study, with one foot on the front force plate and one foot on the back force plate.
the step distance was increased. A trial was deemed a failure if participants uncrossed their arms from their chest during the trial, were unable to successfully reach the force plate, or lost their balance while stepping. Whole body kinematics and ground reaction forces were recorded during all trials. Forty-eight reflective markers were placed bilaterally over selected anatomical landmarks on the head, arms, trunk, and lower extremities (Fig. 1). Marker data was sampled at 100 Hz using the Vicon Motion Analysis T-10 Series System and lowpass filtered using a 4th order zero-phase shift Butterworth filter at 6 Hz. Ground reaction forces were sampled at 1000 Hz using two force plates (AMTI, Watertown, MA, USA) and low-pass filtered using a 4th order zero-phase shift Butterworth filter at 25 Hz. Lower extremity sagittal plane joint torques were estimated using inverse dynamics at the ankle, knee and hip (Winter, 2005). Segmental masses, center of mass location, and mass moment of inertia were based on existing anthropometric models (de Leva, 1996; Pavol et al., 2002). Custom MATLAB code determined the start and end of the trial. The start of a trial was designated when the vertical ground reaction force on the back force plate exceeded the mean of the vertical components from the beginning of data collection by three standard deviations. To establish the end of the trial, the time at which the derivative of the stepping leg heel and stepping leg toe marker in the anterior–posterior direction was less than zero was determined. The end of the trial was the latter of the two times. Visual confirmation was used to verify the points. Upon preliminary analysis of the data, no differences between the left-foot and right-foot stepping trials were determined; therefore, only right foot stepping trials were analyzed. Dependent measures included peak joint torques throughout the trial (start to end) for the ankle, knee and hip of both the stepping (back) and stance (front) leg. Additionally, maximum power absorbed and maximum power generated throughout the
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trial for the ankle, knee, and hip of both legs was calculated. Power was calculated as the product of joint angular velocity and joint torque (Zatsiorsky, 2002). Joint torques were normalized to body mass times height and joint powers were normalized to body mass (Hsiao-Wecksler and Robinovitch, 2007; Judge et al., 1996). Age group (young versus old) differences in weight, height, initial step distance, and maximum completed step distance were compared using Student's t-tests. A one-way repeated measures ANOVA was used to determine the effects of age group on joint kinetics during the maximum completed step distance trial, which could vary between participants. Initially, two statistical models were created to determine effects during maximum step distance. The first was a two-way model with age group, gender, and their interaction, and the second with age group only. Root-meansquare errors for all dependent measures of these two models differed by an average of 0.00003 Nm/(m*kg)for joint torques and 0.00033 W/kg for joint powers, indicating little improvement when including gender in the model, therefore, the one-way model (age group) was chosen. Due the varying abilities of the participants, only the first three step distances were used (average step length, step length plus 10% BH, step length plus 20% BH). A two-way repeated measures mixed model ANOVA was used to determine the effects of age group, step distance, and their interaction on joint kinetics during
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the first three step distances for all participants. Initially, two statistical models were created to determine effects during the first three step distance trials. The first was a three-way model with age group, gender, step distance, and their interactions and the second with age group, step distance, and their interaction. Root-mean-square errors for all dependent measures of these two models differed by an average of 0.001 Nm/(m*kg)for joint torques and 0.0047 W/kg for joint powers, indicating little improvement when including the gender in the model, therefore the two-way model, with age group, step distance, and their interaction was chosen. Upon significant step distance or interaction effect, Tukey's HSD post-hoc analysis was completed for pairwise comparison. All statistical tests were completed in JMP 11.1.1 with significance set at α ¼0.05.
3. Results 3.1. Subject characteristics and step lengths One young female subject was removed from all analyses due to equipment failure during data collection and one old male subject was removed from the increasing step distance analysis as he was unable to complete all three step distances. Young and old
Fig. 2. Ensemble-averaged lower extremity joint torques for the initial step for both young (black) and old (gray) adults. Each trial was normalized from the start of the trial to the end of the trial. Solid lines represent mean behavior and surrounding dotted lines show one standard deviation.
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adults did not differ in height (P ¼0.071) or mass (P ¼0.847). The initial step length, corresponding to the initial force plate separation, was longer in young adults, 0.666(0.057) m compared to old adults, 0.583(0.086) m (P o0.001). This corresponds to 38.6(3.35)% BH for young adults and 35.0(5.31)% BH for old adults (P¼ 0.015). Young adults tended to have larger deviations in joint torque (Fig. 2) and joint power (Fig. 3) compared to old adults over the initial step length trial, with the general trend in shape being similar. Young adults successfully completed a longer maximum step, 1.23 (0.138) m, than old adults, 0.961(0.150) m (Po0.001). Most young adults (n¼13) completed a þ40% BH step; one could only complete þ20% BH and two only þ30% BH, while one young adult completed a þ 50% BH step. In contrast, most old adults completed either a þ20% BH (n¼ 8) or þ30% BH (n¼ 10) step, with one old adult only completing þ10% BH and one stepping þ40% BH. The average step distance increase between increments was 15.3(0.02) cm. 3.2. Ankle kinetics At the maximum step distance, old adults had significantly larger peak ankle plantarflexion torque and maximum power generated by the stepping leg, while young adults had significantly
Table 2 Mean(SD) peak joint torques (Nm/(m*kg)) and maximum power (W/kg) for the maximum step distance, young and old adults, right leg as the stepping leg. Young
Old
p Value
Ankle
Peak plantarflexion, stepping Peak plantarflexion, stance Max. power generated, stepping Max. power generated, stance Max. power absorbed, stepping Max. power absorbed, stance
0.19 0.27 0.43 0.28 0.64 0.15
(0.10) (0.16) (0.36) (0.15) (0.53) (0.12)
0.37 0.25 1.60 0.16 0.16 0.16
(0.11) (0.15) (0.75) (0.11) (0.10) (0.10)
o 0.001* 0.590 o 0.001* 0.002* o 0.001* 0.817
Knee
Peak extension, stepping Peak extension, stance Max. power generated, stepping Max. power generated, stance Max. power absorbed, stepping Max. power absorbed, stance
1.38 0.83 4.12 1.75 1.14 0.21
(0.32) (0.18) (2.17) (0.67) (0.66) (0.22)
0.88 0.63 1.41 1.01 1.14 0.29
(0.33) (0.25) (1.43) (0.45) (0.56) (0.42)
o 0.001* 0.002* o 0.001* o 0.001* 0.961 0.358
Hip
Peak flexion stepping Peak extension, stance Max. power generated, stepping Max. power generated, stance Max. power absorbed, stepping Max. power absorbed, stance
2.12 1.32 3.50 1.93 1.16 2.75
(0.47) (0.37) (1.61) (1.14) ((0.90) (1.25)
1.52 0.79 1.44 1.16 0.93 0.96
(0.60) (0.24) (0.65) (0.50) (0.71) (0.63)
o 0.001* o 0.001* o 0.001* 0.005* 0.441 o 0.001*
Fig. 3. Ensemble-averaged lower extremity joint powers for the initial step for both young (black) and old (gray) adults. Each trial was normalized from the start of the trial to the end of the trial. Solid lines represent mean behavior and surrounding dotted lines show one standard deviation.
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leg for the young was higher for the þ20% BH distance than the first two step distances for the young (age*step distance P¼ 0.007). Maximum ankle power generated by the stepping leg increased as step distance increased for the old (age*step distance Po 0.001). Maximum ankle power absorbed by the stance leg had an interaction effect (P ¼0.006), where the þ10% BH distance was higher than the initial step distance for the old but not different from þ20% BH distance. Maximum ankle power absorbed by the stepping leg was higher in the old adults during the þ 20% BH distance than all other distances (age*step distance P ¼0.002). 3.3. Knee kinetics With the exception of maximum knee power absorbed, young adults had significantly larger peak knee kinetic measures than the old adults during the maximum step distance (Table 2). Peak knee extension torque during the first three step distances increased for the stance leg (Po 0.001) with no effect of age (P ¼0.075) (Fig. 5). Both young and old adults increased peak knee extension torque with increasing step distance for the stepping leg (age*step distance P o0.001). Maximum knee power generated by the stance leg increased for each step distance (P o0.001) and was higher in old adults compared to young (P ¼0.043). Maximum knee power generated by the stepping leg was higher in the þ20% BH distance, for both young and old adults, than all other distances (age*step distance P o0.001). Maximum knee power absorbed by the stance leg increased for each step distance (P o0.001) with no effect of age (P ¼0.052). Maximum knee powered absorbed by the stepping leg had no interaction effect (P¼ 0.689) or main effects (step distance P ¼0.375, age P ¼0.555). 3.4. Hip kinetics
Fig. 4. Normalized peak ankle plantarflexion torque (top), maximum power absorbed (middle), and maximum power generated (bottom) for young (black) and old (grey), stepping (solid line) and stance (dotted line) leg during the all step distances. Step distances of þ 30% BH, þ 40% BH, and þ 50% BH are greyed to indicate these trials were not statistically analyzed due to reduction in sample size. Note that power absorbed is negative but has been changed to allow for comparison to power generated.
larger maximum ankle power generated by the stance leg and maximum ankle power absorbed by the stepping leg (Table 2). There was no age group difference in the other ankle kinetic measures. Old adults decreased peak ankle plantarflexion torque as step distance increased for the stance leg (age*step distance P ¼0.002) (Fig. 4). Peak ankle plantarflexion torque for the initial step for the old was larger than all other step distances. Both young and old adults decreased peak ankle plantarflexion torque with increasing step distances for the stepping leg (age*step distance P o0.001). Maximum ankle power generated by the stance
With the exception of maximum hip power absorbed in the stepping leg, young adults had significantly larger peak hip kinetic measures than the old adults during the maximum step distance (Table 2). Both young and old adults increased peak hip extension torque for the stance leg with increasing step distance (age*step distance P ¼0.018) (Fig. 6). Peak hip flexion torque for the stepping leg increased for each step distance trial (P o0.001) and was higher in young adults compared to old (P ¼0.010). Maximum hip power generated by the stance leg increased for each step distance trial (P o0.001) with no effect of age (P¼ 0.230). Young adults increased maximum hip power generated by the stepping leg with increasing step distance (age*step distance P o0.001). Both young and old adults increased maximum hip power absorbed by the stance leg with increasing step distance (age*step distance Po 0.001). Maximum hip power absorbed by the stepping leg was higher in the þ 10% BH distance compared to the initial step (P o0.001) with no effect of age (P ¼0.237).
4. Discussion Young adults completed a significantly longer step distance than old adults. Young adults were able to complete an average maximum step distance of 70.8% BH compared to old adults who completed an average maximum step distance of 57.8% BH. At the maximum step distance, in general, kinetic measures were greater in the young than in the old. As step distance increased, only peak plantarflexion torque decreased for both legs, in young and old adults. The observation that young adults were able to complete a larger step than old agrees with other studies. Young females had a 16% longer MSL compared to healthy old females (Medell and Alexander, 2000). In another MSL study, young females completed
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Fig. 5. Normalized peak knee extension torque (top), maximum power absorbed (middle), and maximum power generated (bottom) for young (black) and old (grey), stepping (solid line) and stance (dotted line) leg during the all step distances. Step distances of þ 30% BH, þ 40% BH, and þ 50% BH are greyed to indicate these trials were not statistically analyzed due to reduction in sample size. Note that power absorbed is negative but has been changed to allow for comparison to power generated.
a step equal to 79% BH compared to 58% BH for old females (Schulz et al., 2007). A “back only” version of the MSL, which is most similar to the current study, reported no specific distance data (Schulz et al., 2007). Reduced strength and power at the hip and knee resulted in smaller MSL (Schulz et al., 2007). As old adults tend to have less strength at the hip and knee compared to healthy young adults, this may be one reason for the smaller maximum step distance (Johnson et al., 2004; Lindle et al., 1997). Additionally, young adults generated almost double the power at the knee and hip for the stepping leg compared to old adults during the
maximum step distance. Joint power may also be a limiting factor for completing large step distances in old adults, though speed was not controlled for in the current study. Peak plantarflexion torque of the stepping leg decreased as step distance increased and was higher in old adults than young. During the maximum step distance, old adults had almost double the peak plantarflexion torque, and generated approximately three times the maximum power in the stepping leg than young adults. Although a different stepping task, during maximum forward lean recovery, young adults had larger peak plantarflexion torque than old, but, there was a pattern of decreasing plantarflexion torque as step length increased for the old adults (Hsiao-Wecksler and Robinovitch, 2007). Schulz et al. (2007) did not examine plantarflexion torque as step length increased in MSL. Judge et al. (1996) suggested increasing ankle plantarflexor strength will increase step length during normal walking, though this may not be true when recovering from a forward lean or in the current study. In the current study, ankle plantarflexor torque does not appear to be the limiting factor for old adults to complete large step distances. Peak knee extensor torque in the stepping leg increased for both young and old with increasing step distance. The pattern of increasing knee extensor torque with increasing step length was also seen for young and old adults completing the MSL test (Schulz et al., 2013). Using a forward lean protocol, as step length increased, old adults had higher peak knee extensor torque than young for the stepping leg, except at maximum step length (HsiaoWecksler and Robinovitch, 2007). The difference in results may be due to the type of response that is required of the participants. Both the current study and the MSL require a voluntary step response (Schulz et al., 2008). Participants step out and back in the MSL, while participants step forward in this study. There were no timing restrictions with either movement. The forward lean utilized a compensatory step (Hsiao-Wecksler and Robinovitch, 2007). Participants were unaware of when the release would come and had to quickly react to recover from the fall. The quick reaction may be more startling for old adults, causing the knee extensor to peak higher than when given the ability to control the timing. Whether the step was voluntary or compensatory did not have an effect on the pattern of plantarflexor torque. This study has shown the ability to discriminate between young and old adults, with respect to the maximum step distance they can achieve and joint kinetics during that trial, but no comparison to falls was made. The ability for the MSL test to predict future falls varies. One study determined the MSL test was able to predict future falls, though no cutoff value was determined due to the small sample size (Lindemann et al., 2008). Another concluded that the MSL test was not a valid predictor of fall risk for old adults (Bongers et al., 2015). As the “back only” version of the MSL was qualitatively perceived by the participants to be more difficult than the original version, though the specific reasons for this rating was not disclosed and could potentially due to biomechanical challenges or even comfort, the current test may also be more challenging than the original MSL test (Schulz et al., 2007). Because of the potentially increased difficulty of this test, it may have the capability to better discriminate between fallers and nonfallers, based only on their maximum step distance they can achieve. If this method were to be used to discriminate between fallers and non-fallers in a clinical setting, initial step length could be determined by having participants walk a certain number of steps, measuring the total distance traveled, and then calculating average step length. This would eliminate the need for motion capture technology. Additionally, smaller step increments could be used to allow for greater sensitivity in the measurement. Trunk kinematics has been shown to be an important measure in many balance recovery tasks. Old adults who completed one session of practicing recovery from a simulated trip had a greater
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Fig. 6. Normalized peak hip flexion torque (top left), peak hip extension torque (top right), maximum power absorbed (bottom left), and maximum power generated (bottom right) for young (black) and old (grey), stepping (solid line) and stance (dotted line) leg during the all step distances. Step distances of þ 30% BH, þ40% BH, and þ 50% BH are greyed to indicate these trials were not statistically analyzed due to reduction in sample size. Note that power absorbed is negative but has been changed to allow for comparison to power generated.
reduction in trunk angle and time to maximum trunk angle during an actual trip compared to a control group who did not complete training (Bieryla et al., 2007). Using a simulated trip task, the two main discriminating factors between fallers and non-fallers was trunk flexion angle at toe-off and trunk flexion velocity at recovery foot contact (Owings et al., 2001). Additionally, the inability to restabilize the trunk is one factor in the inability to recover from a trip (Pavol et al., 2001). Future investigations combining the study of lower limb joint kinetics while examining trunk kinematics may be another method to distinguish between fallers and non-fallers in a future study. There are several limitations to this study. First, the trials were analyzed only in the sagittal plane. Though the majority of the motion was in this plane, some off-axis rotation may have occurred. The old adults who participated in the study were not screened to determine if they were a high risk for falls. Old adults with a high risk for falls may behave differently, potentially generating less torque and completing a smaller maximum step distance. Speed of the trial was not controlled and may have affected the joint power results. Some step distances required the help of a spotter to get into the correct starting position. At no time did anyone stop the study due to concerns for their safety. Finally, fatigue may have become an issue as step distances increased, though time was given to rest if necessary. In conclusion, young adults were able to complete a longer maximum step distance than old adults, and in general, young adults had larger joint kinetic measures during the maximum step distance. Additionally, joint kinetics increased as step distance
increased for all measures except peak plantarflexor torque. The age group differences in joint kinetics at the maximum step distance may lead to training programs to strengthen the potential limiting factors. If interested in only the maximum step distance participants could complete, this test is easy to administer and may be more challenging than the MSL. Future work should determine if this protocol could be used to discriminate between fallers and non-fallers.
Conflict of interest There are no conflicts of interest for the authors.
Acknowledgments The study was supported through internal funding.
References Bieryla, K.A., Madigan, M.L., Nussbaum, M.A., 2007. Practicing recovery from a simulated trip improves recovery kinematics after an actual trip. Gait Posture 26, 208–213. Bongers, K.T.J., Schoon, Y., Graauwmans, M.J., Schers, H.J., Melis, R.J., Olde Rikkert, M.G.M., 2015. The predictive value of gait speed and maximum step length for falling in community-dwelling older persons. Age Ageing 44, 294–299.
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Carty, C.P., Mills, P., Barrett, R., 2011. Recovery from forward loss of balance in young and older adults using the stepping strategy. Gait Posture 33, 261–267. Carty, C.P., Barrett, R.S., Cronin, N.J., Lichtwark, G.A., Mills, P.M., 2012. Lower limb muscle weakness predicts use of a multiple-versus single-step strategy to recover from forward loss of balance in older adults. J. Gerontol. Seri. A: Biol. Sci. Med. Sci. 67, 1246–1252. Carty, C.P., Cronin, N.J., Nicholson, D., Lichtwark, G.A., Mills, P.M., Kerr, G., Cresswell, A.G., Barrett, R.S., 2015. Reactive stepping behaviour in response to forward loss of balance predicts future falls in community-dwelling older adults. Age Ageing 44, 109–115. Cho, B., Scarpace, D., Alexander, N.B., 2004. Tests of stepping as indicators of mobility, balance, and fall risk in balance‐impaired older adults. J. Am. Geriatr. Soc. 52, 1168–1173. Cyr, M., Smeesters, C., 2007. Instructions limiting the number of steps do not affect the kinetics of the threshold of balance recovery in younger adults. J. Biomech. 40, 2857–2864. de Leva, P., 1996. Adjustments to Zatsiorsky–Seluyanov's segment inertia parameters. J. Biomech. 29, 1223–1230. Hsiao-Wecksler, E.T., Robinovitch, S.N., 2007. The effect of step length on young and elderly women's ability to recover balance. Clin. Biomech. 22, 574–580. Johnson, M.E., Mille, M., Martinez, K.M., Crombie, G., Rogers, M.W., 2004. Agerelated changes in hip abductor and adductor joint torques. Arch. Phys. Med. Rehabil. 85, 593–597. Judge, J.O., Davis 3rd, R.B., Ounpuu, S., 1996. Step length reductions in advanced age: the role of ankle and hip kinetics. J. Gerontol. Ser. A: Biol. Sci. Med. Sci. 51, M303–M312. Lindemann, U., Lundin-Olsson, L., Hauer, K., Wengert, M., Becker, C., Pfeiffer, K., 2008. Maximum step length as a potential screening tool for falls in non-disabled older adults living in the community. Aging Clin. Exp. Res. 20, 394–399. Lindle, R.S., Metter, E.J., Lynch, N.A., Fleg, J.L., Fozard, J.L., Tobin, J., Roy, T.A., Hurley, B.F., 1997. Age and gender comparisons of muscle strength in 654 women and men aged 20–93yr. J. Appl. Physiol. 83, 1581–1587. Madigan, M.L., Lloyd, E.M., 2005. Age-related differences in peak joint torques during the support phase of single-step recovery from a forward fall. J. Gerontol. Ser. A: Biol. Sci. Med. Sci. 60, 910–914.
Medell, J.L., Alexander, N.B., 2000. A clinical measure of maximal and rapid stepping in older women. J. Geronto. Ser. A: Biol. Sci. Med. Sci. 55, M429–M433. Nnodim, J.O., Strasburg, D., Nabozny, M., Nyquist, L., Galecki, A., Chen, S., Alexander, N.B., 2006. Dynamic balance and stepping versus tai chi training to improve balance and stepping in at‐risk older adults. J. Am. Geriatr. Soc. 54, 1825–1831. Owings, T.M., Pavol, M.J., Grabiner, M.D., 2001. Mechanisms of failed recovery following postural perturbations on a motorized treadmill mimic those associated with an actual forward trip. Clin. Biomech. 16, 813–819. Pavol, M.J., Owings, T.M., Foley, K.T., Grabiner, M.D., 2001. Mechanisms leading to a fall from an induced trip in healthy older adults. J. Gerontol. Ser. A: Biol. Sci. Med. Sci. 56, M428–M437. Pavol, M.J., Owings, T.M., Grabiner, M.D., 2002. Body segment inertial parameter estimation for the general population of older adults. J. Biomech. 35, 707–712. Schulz, B.W., Ashton-Miller, J.A., Alexander, N.B., 2008. The effects of age and step length on joint kinematics and kinetics of large out-and-back steps. Clin. Biomech. 23, 609–618. Schulz, B.W., Ashton-Miller, J.A., Alexander, N.B., 2007. Maximum step length: relationships to age and knee and hip extensor capacities. Clin. Biomech. 22, 689–696. Schulz, B.W., Jongprasithporn, M., Hart-Hughes, S.J., Bulat, T., 2013. Effects of step length, age, and fall history on hip and knee kinetics and knee co-contraction during the maximum step length test. Clini. Biomech. 28, 933–940. Thelen, D.G., Wojcik, L.A., Schultz, A.B., Ashton-Miller, J.A., Alexander, N.B., 1997. Age differences in using a rapid step to regain balance during a forward fall. J. Gerontol. Ser. A: Biol. Sci. Med. Sci. 52, M8–M13. Winter, D., 2005. Biomechanics and Motor Control of Human Movement. John Wiley & Sons Inc., Hoboken, NJ. Wojcik, L.A., Thelen, D.G., Schultz, A.B., Ashton-Miller, J.A., Alexander, N.B., 1999. Age and gender differences in single-step recovery from a forward fall. J. Gerontol. Ser. A: Biol. Sci. Med. Sci. 54, M44–M50. Zatsiorsky, V., 2002. Kinetics of Human Movement. Human Kinetics, Champaign, IL.
Contents lists available at ScienceDirect
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Effects of age and step length on joint kinetics during stepping task Kathleen A. Bieryla a,n, Christine Buffinton b a b
Biomedical Engineering Department, Bucknell University, One Dent Drive, Lewisburg, PA 17837, USA Mechanical Engineering Department, Bucknell University, One Dent Drive, Lewisburg, PA 17837, USA
art ic l e i nf o
a b s t r a c t
Article history: Accepted 30 May 2015
Following a balance perturbation, a stepping response is commonly used to regain support, and the distance of the recovery step can vary. To date, no other studies have examined joint kinetics in young and old adults during increasing step distances, when participants are required to bring their rear foot forward. Therefore, the purpose of this study was to examine age-related differences in joint kinetics with increasing step distance. Twenty young and 20 old adults completed the study. Participants completed a step starting from double support, at an initial distance equal to the individual's average step length. The distance was increased by 10% body height until an unsuccessful attempt. A one-way, repeated measures ANOVA was used to determine the effects of age on joint kinetics during the maximum step distance. A two-way, repeated measures, mixed model ANOVA was used to determine the effects of age, step distance, and their interaction on joint kinetics during the first three step distances for all participants. Young adults completed a significantly longer step than old adults. During the maximum step, in general, kinetic measures were greater in the young than in the old. As step distance increased, all but one kinetic measure increased for both young and old adults. This study has shown the ability to discriminate between young and old adults, and could potentially be used in the future to distinguish between fallers and non-fallers. & 2015 Elsevier Ltd. All rights reserved.
Keywords: Step length Old adults Kinetics
1. Introduction Following a balance perturbation, one or more steps are commonly used to regain support. A number of studies have used a forward lean and release protocol to instigate a balance perturbation, simulating a fall (Hsiao-Wecksler and Robinovitch, 2007; Madigan and Lloyd, 2005). Participants lean forward while in a harness and are released with instructions to recover by taking one step, though some studies have focused on comparing multiple steppers to single steppers (Carty et al., 2011, 2012). Instructing participants to limit (or not limit) the number of steps during forward lean recovery was shown to have no effect on lower extremity peak joint torques (Cyr and Smeesters, 2007). Studies show young adults can recover from larger lean angles than old (Madigan and Lloyd, 2005; Thelen et al., 1997; Wojcik et al., 1999). Most of the forward lean and release studies focused on kinematics and kinetics from release to heel contact. One study examined joint kinetics during the support phase of the forward lean protocol, from heel contact to steady state, and found old adults had trends towards larger peak extensor torques at the hip and ankle and significantly lower peak knee extensor torques compared to young adults, indicating different phases of recovery n
Corresponding author. Tel.: þ 1 570 577 2341; fax: þ 1 570 577 3659. E-mail address: [email protected] (K.A. Bieryla).
http://dx.doi.org/10.1016/j.jbiomech.2015.05.028 0021-9290/& 2015 Elsevier Ltd. All rights reserved.
have different joint torque requirements (Madigan and Lloyd, 2005). Additionally, maximum recovery lean magnitude as a percent of body weight and the number of steps to recover from a forward lean at 25% body weight was found to be a predictor of future falls (Carty et al., 2015). These studies provide valuable information, but can also be time consuming and require specialized equipment. The maximum step length (MSL) test has been used as a clinical assessment of balance (Cho et al., 2004; Nnodim et al., 2006). The MSL test requires a person to step out with one leg as far as possible, and then return to the starting position (Medell and Alexander, 2000). The MSL is shorter in old adults compared to young (Medell and Alexander, 2000; Schulz et al., 2008) and hip and knee kinetics were greater for young women compared to old women during MSL (Schulz et al., 2008). During the forward MSL test (step out and back), peak torques occurred during the “push back” phase (stepping back) (Schulz et al., 2007). This may be one reason the authors explored a variation of the MSL, “back only”, where participants started with their feet separated in double support, then returned both feet together by taking a backward step. When participants were instructed to rank the difficulty of the various versions of the MSL, the majority of the participants qualitatively rated the “back only” version of the MSL as the most difficult (Schulz et al., 2007). Both versions of the MSL test require less time to set up than the forward lean protocol as there is no specialized equipment required to place participants into the initial starting position.
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This study explored a movement similar to the MSL “back only” version in that the starting position is also double support. However, in the current study, the participant steps forward, bringing the back foot alongside the front foot, completing the step. As the back stepping movement is less likely during recovery from a fall, the forward stepping movement was examined as a more natural motion after a balance recovery step. This is an important extension to balance-perturbation tests such as the forward lean and release, since adults must also be able to re-initiate forward motion after a balance recovery step(s), and the inability to do so may be another cause of loss of balance. The static starting position isolates a worst-case scenario, when a person does not have momentum to continue forward motion with a second step. To date, no other studies have compared joint kinetics in young and old adults during increasing step distances, starting in double support and completing the step. Therefore the purpose of this study was twofold: to examine age-related differences in the maximum step distance participants are able to complete, and to examine age-related differences in joint kinetics with increasing step distance. It was hypothesized that (1) young adults are able to successfully complete longer step distances than old adults, (2) peak joint kinetics will increase for both groups as step distance increases, and (3) young adults will have larger peak joint kinetics than old adults during their maximum step distance.
2. Methods Twenty young (10 male, 10 female) and 20 old (10 male, 10 female), healthy adults were recruited from the local community to complete the study (Table 1). The study was approved by Bucknell University's Institutional Review Board and written consent was obtained. The study consisted of participants beginning in double support at an initial distance equal to the individual's average step length, and stepping forward with the back foot to bring it alongside the front foot. The distance between the front heel and back heel was increased by 10% of body height (BH) until the participant was unable to complete the step successfully. To determine step length, reflective markers were placed on the right and left heel of the participant. They were then instructed to walk normally in a straight line across the room. After a minimum of three passes, data was recorded using a Vicon Motion Analysis T-10 Series System (Motion Systems Ltd., Centennial, CO, USA). Average step length was calculated from a minimum of three recorded step lengths. The study began with the participant's dominant foot on the front force plate and non-dominant foot on the back force plate (Fig. 1). Dominance was determined by asking the participants with which foot they would kick a soccer ball. Participants were barefoot and instructed to stand relaxed with arms across their chest and look straight ahead. When signaled, they stepped forward, ending with both feet on the front force plate, with heels on a target line. Three trials were attempted with the dominant leg forward followed by three trials with the non-dominant leg forward. Upon successful completion of two out of the three trials, Table 1 Participant characteristics by age group and gender. Mean (standard deviation) reported for age, height, and mass.
Young female (n¼ 10) Young male (n¼ 10) Old female (n¼ 10) Old male (n¼ 10)
Age (yr)
Height (m)
Mass (kg)
20.3 19.6 73.8 77.4
1.64 1.80 1.60 1.74
65.1 76.1 64.7 80.0
(2.0) (1.5) (3.5) (5.6)
(0.08) (0.08) (0.04) (0.06)
(16.7) (11.5) (10.4) (13.0)
Fig. 1. Double support starting position for the study, with one foot on the front force plate and one foot on the back force plate.
the step distance was increased. A trial was deemed a failure if participants uncrossed their arms from their chest during the trial, were unable to successfully reach the force plate, or lost their balance while stepping. Whole body kinematics and ground reaction forces were recorded during all trials. Forty-eight reflective markers were placed bilaterally over selected anatomical landmarks on the head, arms, trunk, and lower extremities (Fig. 1). Marker data was sampled at 100 Hz using the Vicon Motion Analysis T-10 Series System and lowpass filtered using a 4th order zero-phase shift Butterworth filter at 6 Hz. Ground reaction forces were sampled at 1000 Hz using two force plates (AMTI, Watertown, MA, USA) and low-pass filtered using a 4th order zero-phase shift Butterworth filter at 25 Hz. Lower extremity sagittal plane joint torques were estimated using inverse dynamics at the ankle, knee and hip (Winter, 2005). Segmental masses, center of mass location, and mass moment of inertia were based on existing anthropometric models (de Leva, 1996; Pavol et al., 2002). Custom MATLAB code determined the start and end of the trial. The start of a trial was designated when the vertical ground reaction force on the back force plate exceeded the mean of the vertical components from the beginning of data collection by three standard deviations. To establish the end of the trial, the time at which the derivative of the stepping leg heel and stepping leg toe marker in the anterior–posterior direction was less than zero was determined. The end of the trial was the latter of the two times. Visual confirmation was used to verify the points. Upon preliminary analysis of the data, no differences between the left-foot and right-foot stepping trials were determined; therefore, only right foot stepping trials were analyzed. Dependent measures included peak joint torques throughout the trial (start to end) for the ankle, knee and hip of both the stepping (back) and stance (front) leg. Additionally, maximum power absorbed and maximum power generated throughout the
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trial for the ankle, knee, and hip of both legs was calculated. Power was calculated as the product of joint angular velocity and joint torque (Zatsiorsky, 2002). Joint torques were normalized to body mass times height and joint powers were normalized to body mass (Hsiao-Wecksler and Robinovitch, 2007; Judge et al., 1996). Age group (young versus old) differences in weight, height, initial step distance, and maximum completed step distance were compared using Student's t-tests. A one-way repeated measures ANOVA was used to determine the effects of age group on joint kinetics during the maximum completed step distance trial, which could vary between participants. Initially, two statistical models were created to determine effects during maximum step distance. The first was a two-way model with age group, gender, and their interaction, and the second with age group only. Root-meansquare errors for all dependent measures of these two models differed by an average of 0.00003 Nm/(m*kg)for joint torques and 0.00033 W/kg for joint powers, indicating little improvement when including gender in the model, therefore, the one-way model (age group) was chosen. Due the varying abilities of the participants, only the first three step distances were used (average step length, step length plus 10% BH, step length plus 20% BH). A two-way repeated measures mixed model ANOVA was used to determine the effects of age group, step distance, and their interaction on joint kinetics during
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the first three step distances for all participants. Initially, two statistical models were created to determine effects during the first three step distance trials. The first was a three-way model with age group, gender, step distance, and their interactions and the second with age group, step distance, and their interaction. Root-mean-square errors for all dependent measures of these two models differed by an average of 0.001 Nm/(m*kg)for joint torques and 0.0047 W/kg for joint powers, indicating little improvement when including the gender in the model, therefore the two-way model, with age group, step distance, and their interaction was chosen. Upon significant step distance or interaction effect, Tukey's HSD post-hoc analysis was completed for pairwise comparison. All statistical tests were completed in JMP 11.1.1 with significance set at α ¼0.05.
3. Results 3.1. Subject characteristics and step lengths One young female subject was removed from all analyses due to equipment failure during data collection and one old male subject was removed from the increasing step distance analysis as he was unable to complete all three step distances. Young and old
Fig. 2. Ensemble-averaged lower extremity joint torques for the initial step for both young (black) and old (gray) adults. Each trial was normalized from the start of the trial to the end of the trial. Solid lines represent mean behavior and surrounding dotted lines show one standard deviation.
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adults did not differ in height (P ¼0.071) or mass (P ¼0.847). The initial step length, corresponding to the initial force plate separation, was longer in young adults, 0.666(0.057) m compared to old adults, 0.583(0.086) m (P o0.001). This corresponds to 38.6(3.35)% BH for young adults and 35.0(5.31)% BH for old adults (P¼ 0.015). Young adults tended to have larger deviations in joint torque (Fig. 2) and joint power (Fig. 3) compared to old adults over the initial step length trial, with the general trend in shape being similar. Young adults successfully completed a longer maximum step, 1.23 (0.138) m, than old adults, 0.961(0.150) m (Po0.001). Most young adults (n¼13) completed a þ40% BH step; one could only complete þ20% BH and two only þ30% BH, while one young adult completed a þ 50% BH step. In contrast, most old adults completed either a þ20% BH (n¼ 8) or þ30% BH (n¼ 10) step, with one old adult only completing þ10% BH and one stepping þ40% BH. The average step distance increase between increments was 15.3(0.02) cm. 3.2. Ankle kinetics At the maximum step distance, old adults had significantly larger peak ankle plantarflexion torque and maximum power generated by the stepping leg, while young adults had significantly
Table 2 Mean(SD) peak joint torques (Nm/(m*kg)) and maximum power (W/kg) for the maximum step distance, young and old adults, right leg as the stepping leg. Young
Old
p Value
Ankle
Peak plantarflexion, stepping Peak plantarflexion, stance Max. power generated, stepping Max. power generated, stance Max. power absorbed, stepping Max. power absorbed, stance
0.19 0.27 0.43 0.28 0.64 0.15
(0.10) (0.16) (0.36) (0.15) (0.53) (0.12)
0.37 0.25 1.60 0.16 0.16 0.16
(0.11) (0.15) (0.75) (0.11) (0.10) (0.10)
o 0.001* 0.590 o 0.001* 0.002* o 0.001* 0.817
Knee
Peak extension, stepping Peak extension, stance Max. power generated, stepping Max. power generated, stance Max. power absorbed, stepping Max. power absorbed, stance
1.38 0.83 4.12 1.75 1.14 0.21
(0.32) (0.18) (2.17) (0.67) (0.66) (0.22)
0.88 0.63 1.41 1.01 1.14 0.29
(0.33) (0.25) (1.43) (0.45) (0.56) (0.42)
o 0.001* 0.002* o 0.001* o 0.001* 0.961 0.358
Hip
Peak flexion stepping Peak extension, stance Max. power generated, stepping Max. power generated, stance Max. power absorbed, stepping Max. power absorbed, stance
2.12 1.32 3.50 1.93 1.16 2.75
(0.47) (0.37) (1.61) (1.14) ((0.90) (1.25)
1.52 0.79 1.44 1.16 0.93 0.96
(0.60) (0.24) (0.65) (0.50) (0.71) (0.63)
o 0.001* o 0.001* o 0.001* 0.005* 0.441 o 0.001*
Fig. 3. Ensemble-averaged lower extremity joint powers for the initial step for both young (black) and old (gray) adults. Each trial was normalized from the start of the trial to the end of the trial. Solid lines represent mean behavior and surrounding dotted lines show one standard deviation.
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leg for the young was higher for the þ20% BH distance than the first two step distances for the young (age*step distance P¼ 0.007). Maximum ankle power generated by the stepping leg increased as step distance increased for the old (age*step distance Po 0.001). Maximum ankle power absorbed by the stance leg had an interaction effect (P ¼0.006), where the þ10% BH distance was higher than the initial step distance for the old but not different from þ20% BH distance. Maximum ankle power absorbed by the stepping leg was higher in the old adults during the þ 20% BH distance than all other distances (age*step distance P ¼0.002). 3.3. Knee kinetics With the exception of maximum knee power absorbed, young adults had significantly larger peak knee kinetic measures than the old adults during the maximum step distance (Table 2). Peak knee extension torque during the first three step distances increased for the stance leg (Po 0.001) with no effect of age (P ¼0.075) (Fig. 5). Both young and old adults increased peak knee extension torque with increasing step distance for the stepping leg (age*step distance P o0.001). Maximum knee power generated by the stance leg increased for each step distance (P o0.001) and was higher in old adults compared to young (P ¼0.043). Maximum knee power generated by the stepping leg was higher in the þ20% BH distance, for both young and old adults, than all other distances (age*step distance P o0.001). Maximum knee power absorbed by the stance leg increased for each step distance (P o0.001) with no effect of age (P ¼0.052). Maximum knee powered absorbed by the stepping leg had no interaction effect (P¼ 0.689) or main effects (step distance P ¼0.375, age P ¼0.555). 3.4. Hip kinetics
Fig. 4. Normalized peak ankle plantarflexion torque (top), maximum power absorbed (middle), and maximum power generated (bottom) for young (black) and old (grey), stepping (solid line) and stance (dotted line) leg during the all step distances. Step distances of þ 30% BH, þ 40% BH, and þ 50% BH are greyed to indicate these trials were not statistically analyzed due to reduction in sample size. Note that power absorbed is negative but has been changed to allow for comparison to power generated.
larger maximum ankle power generated by the stance leg and maximum ankle power absorbed by the stepping leg (Table 2). There was no age group difference in the other ankle kinetic measures. Old adults decreased peak ankle plantarflexion torque as step distance increased for the stance leg (age*step distance P ¼0.002) (Fig. 4). Peak ankle plantarflexion torque for the initial step for the old was larger than all other step distances. Both young and old adults decreased peak ankle plantarflexion torque with increasing step distances for the stepping leg (age*step distance P o0.001). Maximum ankle power generated by the stance
With the exception of maximum hip power absorbed in the stepping leg, young adults had significantly larger peak hip kinetic measures than the old adults during the maximum step distance (Table 2). Both young and old adults increased peak hip extension torque for the stance leg with increasing step distance (age*step distance P ¼0.018) (Fig. 6). Peak hip flexion torque for the stepping leg increased for each step distance trial (P o0.001) and was higher in young adults compared to old (P ¼0.010). Maximum hip power generated by the stance leg increased for each step distance trial (P o0.001) with no effect of age (P¼ 0.230). Young adults increased maximum hip power generated by the stepping leg with increasing step distance (age*step distance P o0.001). Both young and old adults increased maximum hip power absorbed by the stance leg with increasing step distance (age*step distance Po 0.001). Maximum hip power absorbed by the stepping leg was higher in the þ 10% BH distance compared to the initial step (P o0.001) with no effect of age (P ¼0.237).
4. Discussion Young adults completed a significantly longer step distance than old adults. Young adults were able to complete an average maximum step distance of 70.8% BH compared to old adults who completed an average maximum step distance of 57.8% BH. At the maximum step distance, in general, kinetic measures were greater in the young than in the old. As step distance increased, only peak plantarflexion torque decreased for both legs, in young and old adults. The observation that young adults were able to complete a larger step than old agrees with other studies. Young females had a 16% longer MSL compared to healthy old females (Medell and Alexander, 2000). In another MSL study, young females completed
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Fig. 5. Normalized peak knee extension torque (top), maximum power absorbed (middle), and maximum power generated (bottom) for young (black) and old (grey), stepping (solid line) and stance (dotted line) leg during the all step distances. Step distances of þ 30% BH, þ 40% BH, and þ 50% BH are greyed to indicate these trials were not statistically analyzed due to reduction in sample size. Note that power absorbed is negative but has been changed to allow for comparison to power generated.
a step equal to 79% BH compared to 58% BH for old females (Schulz et al., 2007). A “back only” version of the MSL, which is most similar to the current study, reported no specific distance data (Schulz et al., 2007). Reduced strength and power at the hip and knee resulted in smaller MSL (Schulz et al., 2007). As old adults tend to have less strength at the hip and knee compared to healthy young adults, this may be one reason for the smaller maximum step distance (Johnson et al., 2004; Lindle et al., 1997). Additionally, young adults generated almost double the power at the knee and hip for the stepping leg compared to old adults during the
maximum step distance. Joint power may also be a limiting factor for completing large step distances in old adults, though speed was not controlled for in the current study. Peak plantarflexion torque of the stepping leg decreased as step distance increased and was higher in old adults than young. During the maximum step distance, old adults had almost double the peak plantarflexion torque, and generated approximately three times the maximum power in the stepping leg than young adults. Although a different stepping task, during maximum forward lean recovery, young adults had larger peak plantarflexion torque than old, but, there was a pattern of decreasing plantarflexion torque as step length increased for the old adults (Hsiao-Wecksler and Robinovitch, 2007). Schulz et al. (2007) did not examine plantarflexion torque as step length increased in MSL. Judge et al. (1996) suggested increasing ankle plantarflexor strength will increase step length during normal walking, though this may not be true when recovering from a forward lean or in the current study. In the current study, ankle plantarflexor torque does not appear to be the limiting factor for old adults to complete large step distances. Peak knee extensor torque in the stepping leg increased for both young and old with increasing step distance. The pattern of increasing knee extensor torque with increasing step length was also seen for young and old adults completing the MSL test (Schulz et al., 2013). Using a forward lean protocol, as step length increased, old adults had higher peak knee extensor torque than young for the stepping leg, except at maximum step length (HsiaoWecksler and Robinovitch, 2007). The difference in results may be due to the type of response that is required of the participants. Both the current study and the MSL require a voluntary step response (Schulz et al., 2008). Participants step out and back in the MSL, while participants step forward in this study. There were no timing restrictions with either movement. The forward lean utilized a compensatory step (Hsiao-Wecksler and Robinovitch, 2007). Participants were unaware of when the release would come and had to quickly react to recover from the fall. The quick reaction may be more startling for old adults, causing the knee extensor to peak higher than when given the ability to control the timing. Whether the step was voluntary or compensatory did not have an effect on the pattern of plantarflexor torque. This study has shown the ability to discriminate between young and old adults, with respect to the maximum step distance they can achieve and joint kinetics during that trial, but no comparison to falls was made. The ability for the MSL test to predict future falls varies. One study determined the MSL test was able to predict future falls, though no cutoff value was determined due to the small sample size (Lindemann et al., 2008). Another concluded that the MSL test was not a valid predictor of fall risk for old adults (Bongers et al., 2015). As the “back only” version of the MSL was qualitatively perceived by the participants to be more difficult than the original version, though the specific reasons for this rating was not disclosed and could potentially due to biomechanical challenges or even comfort, the current test may also be more challenging than the original MSL test (Schulz et al., 2007). Because of the potentially increased difficulty of this test, it may have the capability to better discriminate between fallers and nonfallers, based only on their maximum step distance they can achieve. If this method were to be used to discriminate between fallers and non-fallers in a clinical setting, initial step length could be determined by having participants walk a certain number of steps, measuring the total distance traveled, and then calculating average step length. This would eliminate the need for motion capture technology. Additionally, smaller step increments could be used to allow for greater sensitivity in the measurement. Trunk kinematics has been shown to be an important measure in many balance recovery tasks. Old adults who completed one session of practicing recovery from a simulated trip had a greater
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Fig. 6. Normalized peak hip flexion torque (top left), peak hip extension torque (top right), maximum power absorbed (bottom left), and maximum power generated (bottom right) for young (black) and old (grey), stepping (solid line) and stance (dotted line) leg during the all step distances. Step distances of þ 30% BH, þ40% BH, and þ 50% BH are greyed to indicate these trials were not statistically analyzed due to reduction in sample size. Note that power absorbed is negative but has been changed to allow for comparison to power generated.
reduction in trunk angle and time to maximum trunk angle during an actual trip compared to a control group who did not complete training (Bieryla et al., 2007). Using a simulated trip task, the two main discriminating factors between fallers and non-fallers was trunk flexion angle at toe-off and trunk flexion velocity at recovery foot contact (Owings et al., 2001). Additionally, the inability to restabilize the trunk is one factor in the inability to recover from a trip (Pavol et al., 2001). Future investigations combining the study of lower limb joint kinetics while examining trunk kinematics may be another method to distinguish between fallers and non-fallers in a future study. There are several limitations to this study. First, the trials were analyzed only in the sagittal plane. Though the majority of the motion was in this plane, some off-axis rotation may have occurred. The old adults who participated in the study were not screened to determine if they were a high risk for falls. Old adults with a high risk for falls may behave differently, potentially generating less torque and completing a smaller maximum step distance. Speed of the trial was not controlled and may have affected the joint power results. Some step distances required the help of a spotter to get into the correct starting position. At no time did anyone stop the study due to concerns for their safety. Finally, fatigue may have become an issue as step distances increased, though time was given to rest if necessary. In conclusion, young adults were able to complete a longer maximum step distance than old adults, and in general, young adults had larger joint kinetic measures during the maximum step distance. Additionally, joint kinetics increased as step distance
increased for all measures except peak plantarflexor torque. The age group differences in joint kinetics at the maximum step distance may lead to training programs to strengthen the potential limiting factors. If interested in only the maximum step distance participants could complete, this test is easy to administer and may be more challenging than the MSL. Future work should determine if this protocol could be used to discriminate between fallers and non-fallers.
Conflict of interest There are no conflicts of interest for the authors.
Acknowledgments The study was supported through internal funding.
References Bieryla, K.A., Madigan, M.L., Nussbaum, M.A., 2007. Practicing recovery from a simulated trip improves recovery kinematics after an actual trip. Gait Posture 26, 208–213. Bongers, K.T.J., Schoon, Y., Graauwmans, M.J., Schers, H.J., Melis, R.J., Olde Rikkert, M.G.M., 2015. The predictive value of gait speed and maximum step length for falling in community-dwelling older persons. Age Ageing 44, 294–299.
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Carty, C.P., Mills, P., Barrett, R., 2011. Recovery from forward loss of balance in young and older adults using the stepping strategy. Gait Posture 33, 261–267. Carty, C.P., Barrett, R.S., Cronin, N.J., Lichtwark, G.A., Mills, P.M., 2012. Lower limb muscle weakness predicts use of a multiple-versus single-step strategy to recover from forward loss of balance in older adults. J. Gerontol. Seri. A: Biol. Sci. Med. Sci. 67, 1246–1252. Carty, C.P., Cronin, N.J., Nicholson, D., Lichtwark, G.A., Mills, P.M., Kerr, G., Cresswell, A.G., Barrett, R.S., 2015. Reactive stepping behaviour in response to forward loss of balance predicts future falls in community-dwelling older adults. Age Ageing 44, 109–115. Cho, B., Scarpace, D., Alexander, N.B., 2004. Tests of stepping as indicators of mobility, balance, and fall risk in balance‐impaired older adults. J. Am. Geriatr. Soc. 52, 1168–1173. Cyr, M., Smeesters, C., 2007. Instructions limiting the number of steps do not affect the kinetics of the threshold of balance recovery in younger adults. J. Biomech. 40, 2857–2864. de Leva, P., 1996. Adjustments to Zatsiorsky–Seluyanov's segment inertia parameters. J. Biomech. 29, 1223–1230. Hsiao-Wecksler, E.T., Robinovitch, S.N., 2007. The effect of step length on young and elderly women's ability to recover balance. Clin. Biomech. 22, 574–580. Johnson, M.E., Mille, M., Martinez, K.M., Crombie, G., Rogers, M.W., 2004. Agerelated changes in hip abductor and adductor joint torques. Arch. Phys. Med. Rehabil. 85, 593–597. Judge, J.O., Davis 3rd, R.B., Ounpuu, S., 1996. Step length reductions in advanced age: the role of ankle and hip kinetics. J. Gerontol. Ser. A: Biol. Sci. Med. Sci. 51, M303–M312. Lindemann, U., Lundin-Olsson, L., Hauer, K., Wengert, M., Becker, C., Pfeiffer, K., 2008. Maximum step length as a potential screening tool for falls in non-disabled older adults living in the community. Aging Clin. Exp. Res. 20, 394–399. Lindle, R.S., Metter, E.J., Lynch, N.A., Fleg, J.L., Fozard, J.L., Tobin, J., Roy, T.A., Hurley, B.F., 1997. Age and gender comparisons of muscle strength in 654 women and men aged 20–93yr. J. Appl. Physiol. 83, 1581–1587. Madigan, M.L., Lloyd, E.M., 2005. Age-related differences in peak joint torques during the support phase of single-step recovery from a forward fall. J. Gerontol. Ser. A: Biol. Sci. Med. Sci. 60, 910–914.
Medell, J.L., Alexander, N.B., 2000. A clinical measure of maximal and rapid stepping in older women. J. Geronto. Ser. A: Biol. Sci. Med. Sci. 55, M429–M433. Nnodim, J.O., Strasburg, D., Nabozny, M., Nyquist, L., Galecki, A., Chen, S., Alexander, N.B., 2006. Dynamic balance and stepping versus tai chi training to improve balance and stepping in at‐risk older adults. J. Am. Geriatr. Soc. 54, 1825–1831. Owings, T.M., Pavol, M.J., Grabiner, M.D., 2001. Mechanisms of failed recovery following postural perturbations on a motorized treadmill mimic those associated with an actual forward trip. Clin. Biomech. 16, 813–819. Pavol, M.J., Owings, T.M., Foley, K.T., Grabiner, M.D., 2001. Mechanisms leading to a fall from an induced trip in healthy older adults. J. Gerontol. Ser. A: Biol. Sci. Med. Sci. 56, M428–M437. Pavol, M.J., Owings, T.M., Grabiner, M.D., 2002. Body segment inertial parameter estimation for the general population of older adults. J. Biomech. 35, 707–712. Schulz, B.W., Ashton-Miller, J.A., Alexander, N.B., 2008. The effects of age and step length on joint kinematics and kinetics of large out-and-back steps. Clin. Biomech. 23, 609–618. Schulz, B.W., Ashton-Miller, J.A., Alexander, N.B., 2007. Maximum step length: relationships to age and knee and hip extensor capacities. Clin. Biomech. 22, 689–696. Schulz, B.W., Jongprasithporn, M., Hart-Hughes, S.J., Bulat, T., 2013. Effects of step length, age, and fall history on hip and knee kinetics and knee co-contraction during the maximum step length test. Clini. Biomech. 28, 933–940. Thelen, D.G., Wojcik, L.A., Schultz, A.B., Ashton-Miller, J.A., Alexander, N.B., 1997. Age differences in using a rapid step to regain balance during a forward fall. J. Gerontol. Ser. A: Biol. Sci. Med. Sci. 52, M8–M13. Winter, D., 2005. Biomechanics and Motor Control of Human Movement. John Wiley & Sons Inc., Hoboken, NJ. Wojcik, L.A., Thelen, D.G., Schultz, A.B., Ashton-Miller, J.A., Alexander, N.B., 1999. Age and gender differences in single-step recovery from a forward fall. J. Gerontol. Ser. A: Biol. Sci. Med. Sci. 54, M44–M50. Zatsiorsky, V., 2002. Kinetics of Human Movement. Human Kinetics, Champaign, IL.