Biomechanical gait alterations independent of speed in the healthy elderly: Evidence for specific limiting impairments

317

Biomechanical Gait Alterations Independent of Speed in the Healthy Elderly: Evidence for Specific Limiting Impairments D. Casey Kerrigan, MD, Mary K. Todd, BA, Ugo Della Croce, PhD, Lewis A. Lipsitz, MD, James J. Collins, PhD ABSTRACT. Kerrigan DC, Todd MK, Della Croce U, Lipsitz LA, Collins JJ. Biomechanical gait alterations independent of speed in the healthy elderly: evidence for specific limiting impairments. Arch Phys Med Rehabi11998;79:317-322.

Objectives: It is not known whether changes in the biomechanics of elderly gait are related to aging per se, or to reduced walking speed in this population. The goals of the present study were to identify specific biomechanical changes, independent of speed, that might impair gait performance in healthy older people by identifying age-associated changes in the biomechanics of gait, and to determine which of these changes persist at increased walking speed. Design: Stereophotogrammetric and force platform data were collected, Differences in peak joint motion (kinematic) and joint moment and power (kinetic) values between healthy young and elderly subjects at comfortable and increased walking speed were measured. Setting: A gait laboratory. Subjects: Thirty-one healthy elderly (age 65 to 84 years) and 31 healthy young adult subjects (age 18 to 36 years), all without known neurologic, musculoskeletal, cardiac, or pulmonary problems. Main Outcome Measures: All major peak kinematic and kinetic variables during the gait cycle. Results: Several kinematic and kinetic differences between young and elderly adults were found that did not persist when walking speed was increased. Differences that persisted at both comfortable and fast walking speeds were reduced peak hip extension, increased anterior pelvic tilt, and reduced ankle plantarflexion and ankle power generation. Conclusion: Gait performance in the elderly may be limited by both subtle hip flexion contracture and ankle plantarflexor concentric weakness. Results of the current study should motivate future experimental trials of specific hip flexor stretching and ankle plantarflexor concentric strengthening exercises to preserve and potentially improve walking performance in the elderly.

© 1998 by the American Congress of Rehabilitation Medicine and the American Academy of Physical Medicine and Rehabilitation

From the Harvard Medical School Department of Physical Medicine and Rehabilitation (Drs. Kerrigan, Della Croce), Spaulding Rehabilitation Hospital (Dr. Kerrigan, Ms. Todd, Dr. Della Croce), Harvard Medical School Division on Aging and Hebrew Rehabilitation Center for Aged (Dr. Lipsitz), and Boston University Department of Biomechanical Engineering (Dr. Collins), Boston, MA; and Cattedra Tecnologie Biomediche, Universit~t di Sassari (Dr. Della Croce), Sassari, Italy. Submitted for publication June 23, 1997. Accepted September 24, 1997. Supported in part by Public Health Service grant NIH HD01071-03 and by the Ellison Foundation. Subjects were recruited with the support of the Claude D. Pepper Older Americans Independence Center grant AG08812. No commercial party having a direct financial interest in the results of the research supporting this article has or will confer a benefit upon the authors or upon any organization with which the authors are associated. Reprint requests to D. Casey Kerrigan, MD, MS, Harvard Medical School Department of Physical Medicine and Rehabilitation, Spaulding Rehabilitation Hospital, 125 Nashua Street, Boston, MA 02114. © 1998 by the American Congress of Rehabilitation Medicine and the American Academy of Physical Medicine and Rehabilitation 0003-9993/98/7903-455553.00/0

LTHOUGH AGE-ASSOCIATED changes in muscle strength, joint mobility, and balance are well documented, A the specific mechanisms for decline in walking performance in the elderly are unclear. It is possible that many of these changes are related to alterations in walking speed rather than aging per se. Given the importance of maintaining walking in the elderly with respect to both health and function, it would be useful to identify specific age-associated changes or impairments that could potentially limit gait performance. If specific, functionally significant impairments are found, then rehabilitation efforts can be focused on preventing and reversing these to maintain and improve walking performance in the elderly. Studies of dynamic joint range of motion (kinematics) and joint moments of forces and joint power generation and absorptions (kinetics) during walking should be useful to help pinpoint functionally significant impairments. 1 Early detection of such impairments in the gait patterns of elderly subjects may help to identify potential fall situations or other related risks. 2 A number of studies comparing kinematics between elderly and young adult subjects 3,1,4-11 have reported subtle ageassociated reductions in total joint ranges, particularly about the hip and ankle. Comfortable walking speed, which probably best represents overall walking performance, 12 declines with advanced age beginning in approximately the seventh decade of life. 3,H,13,14 It is not clear whether the observed age-associated changes in walking are the direct result of a slower walking speed or are the result of specific impairments. Few kinetic studies on aging have been performed to date. 1,4,6,15 Crowinshield and colleagues 15 reported ageassociated reductions in hip moment of force. Both Winter and colleagues 1,4 and Judge and colleagues 6 studied age-associated changes in peak joint powers and reported specific ageassociated reductions in peak ankle joint power generation at preswing, which is consistent with kinematic findings of reduced peak ankle plantarflexion. 1,3,s Judge and colleagues 6 also preliminarily noted in a subset of five subjects that a reduction in ankle power generation persisted at fast walking speed, however, there has been no study to date that comprehensively evaluates the effect of velocity on all age-associated changes in gait. While a number of age-associated changes in gait have been previously described, the potential mechanisms or reasons for these changes are as yet unknown. Because kinematic and kinetic values depend on the speed of walking,~ both kinematic and kinetic changes in elderly gait could be attributed to an age-associated reduction in walking speed. The goal of this study was to identify specific kinematic and kinetic changes in the gait of healthy elderly subjects, and to determine whether these changes persisted in elderly people at fast walking speed.

METHODS The population studied consisted of 62 subjects: 31 young healthy, nondisabled adult subjects, age 18 to 36 years; and 31 elderly healthy, nondisabled subjects, age 65 to 84 years. Elderly subjects were recruited from the Boston area by the Harvard Cooperative Program on Aging subject registry, and completed a health questionnaire with that organization prior to participation in the current study. Young subjects included Arch Phys Med Rehabil Vo! 79, March 1998

SPECIFIC GAIT LIMITATIONS IN HEALTHY ELDERLY, Kerrigan

318

hospital staff, staff spouses, and nearby financial district and federal building employees. Subjects recruited for this study were healthy, without known musculoskeletal, neurologic, cardiac, or pulmonary diagnoses. Elderly subjects had no history of frequent falls. Methods were approved by our Institutional Review Board and an informed consent was obtained from each subject. Subjects were asked to first stand and then walk barefoot at their comfortable walking speed across a 30-foot gait laboratory walkway. Each of the elderly subjects and five of the young adult subjects were also asked to "walk fast" across the same walkway. They were not asked to restrict their movement, including arm swing, for any trial. Sagittal kinematic and kinetic data from bilateral lower extremities and the pelvis over three walking trials were collected at comfortable and fast walking speeds. The methodology for data collection has been described elsewhere. 16:7 Briefly, infrared reflective markers were attached to the subjects' skin over 15 bony landmarks on the pelvis and bilateral lower extremities and an optoelectronic motion analysis system a with four video cameras was used to measure the three-dimensional (3-D) coordinates of these markers at 100 frames per second. ~8,19 Ground reaction forces were measured synchronously with the kinematic data using two staggered force platforms b imbedded in the walkway. A commercialized protocol, SAFLo (Servizio di Analisi della Funzionalita' Locomotoria) a developed by Pedotti and Frigo, 2°

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was used to calculate the lower extremity sagittal plane kinematics and kinetics and pelvis motion in three planes, with respect to both a laboratory coordinate system and a body coordinate system. Moments and powers were normalized for body weight and height and reported as external, in newton meters per kilogram meters (Nm/kg-m) and watts per kilogram meters (W/kg-m), respectively. Gait velocity and stride length were obtained using the force platform and kinematic information to define initial foot contact times and distance parameters. Kinematic and kinetic data were graphed over 2% intervals of the gait cycle. Graphs of each trial for each subject as well as the averaged data from all subjects were visually inspected. Qualitative differences in the graphs between age groups and between fast and comfortable speeds were assessed. Twentyeight peak values were evaluated. The terminology of gait cycle events reported by Perry was adopted to define locations in the gait cycle of the peak values, zl All major kinematic and kinetic peaks (figs 1 and 2) were compared statistically between age groups using an unpaired student's t test, taking the average of six trials for each subject for each lower extremity variable (three on each side) and three trials for each subject for the pelvis. An additional analysis was performed using a nested, mixed-effects analysis of variance (ANOVA) model to control for potential gender effect interactions, variances between trials and for all lower extremity measures, variances between the two sides, c The ANOVA model demonstrated no significant

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Arch Phys Med Rehabil Vol 79, March 1998

SPECIFIC GAIT LIMITATIONS IN HEALTHY ELDERLY, Kerrigan

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interactions between age group and gender, trial, or side for any of the variables. Moreover, resultant p values for age-group differences were essentially the same with either statistical method, and accordingly, p values for only the t test results are displayed. Demographic and temporal variables were also compared using an unpaired t test. Paired t tests were used to compare peak kinematic and kinetic differences between comfortable and fast walking speeds. Statistical significance was defined at p < .05. A con'ection for multiple comparisons was not made a priori because of the nature of our investigation, ie, each possible parameter demonstrating significant difference, even if because of chance, deserved further analysis and discussion. RESULTS Results are presented as mean + 1 standard deviation (SD). The elderly subjects ranged in age from 65 to 84 years (average age 72.7 _+ 5.5 yrs), and included 14 men and 17 women. The young adult subjects ranged in age from 18 to 36 years (average age 28.5 _+ 4.9 yrs) and also included 14 men and 17 women. The elderly subjects were statistically significantly shorter in height (1.62 __ .09 versus 1.72 + . 10m, p = .001) but were not significantly different in weight (68.3 -+ 12.9 versus 68.5 + 13.1kg). Temporal parameter differences are listed in table l. The comfortable speed of walking was significantly slower in elderly compared with young adults (1.19-+ .13 versus 1.37 _+ .17rrdsec, p < .001). The fast walking speed of the elderly group significantly exceeded the comfortable walking speed of the young group (1.55 +- .20 versus 1.37 4-. 17m/ sec, p = .001). Similarly, stride length was reduced in the elderly compared with the young adults at comfortable walking speed (1.20 _+ . 12 versus 1.38 -+ . 1 lm, p < .001) and increased at fast walking speed to values that were slightly less than, although not significantly different from, the stride length in Table 1: Temporal Parameters

Temporal Parameters

Young (n - 31) Comfortable Mean (SD)

Elderly (n = 31) Comfortable Mean (SD)

Velocity, m/sec Cadence, steps/min Stride length, m Double support %

1.37 (.17) 119 (10) 1.38 (.11) 23.8 (2.3)

1.19 (.13) 119 (9) 1.20 (.12) 24.9 (2.8)

Fast Mean (SD)

1.55 140 1.33 23.5

(.20) (17) (.14) (2.9)

319

young adults walking at comfortable speed (1.33 _+. 14 versus 1.38 + .llm, p = .100). Joint kinematic and kinetic data averaged over a full gait cycle for the elderly subjects walking at both comfortable and fast speed and the young subjects walking at comfortable speed are plotted in figure 1. The sagittal plane pelvic motion is illustrated in figure 2. These graphs show similar basic patterns between elderly comfortable and fast and young comfortable walking speeds, with some notable differences in amplitudes of peak values. The actual mean kinematic and kinetic values are listed in tables 2 and 3, respectively. Statistically significant reductions in absolute peak values for elderly compared with young adult subjects at comfortable walking, ie, age-associated kinematic and kinetic peak reductions, were observed in 11 of 28 parameters. Table 4 summarizes the results of comparisons for each of these 11 parameters, between (1) elderly and young comfortable walking, (2) elderly fast and young comfortable walking, and (3) elderly comfortable and fast walking. Of these 11 parameters found to be significantly different between the young and elderly groups, only 4 remained persistently significant at both comfortable and fast speeds. These four parameters were peak hip extension, peak ankle plantarflexion, peak ankle plantarflexor power generation, and anterior pelvic tilt. Reduction in kinematic and kinetic values did not persist at fast walking speed in any of the other parameters. There were no significant differences between elderly fast and young comfortable walking for hip flexion moment in stance, knee extension moment at initial contact, knee flexion moment in midstance, knee flexion moment in preswing, or knee power absorption in loading response. For knee power generation in midstance and knee power absorption, the elderly fast peak values significantly exceeded the young comfortable peak values. Paired t test comparisons between elderly fast and elderly comfortable walking revealed that peak hip extension and ankle plantarflexion did not significantly increase (p = .815 and. 166, respectively) while peak anterior pelvic tilt and ankle plantarflexion power did in fact significantly increase between slow and fast walking (p = .009 and .002, respectively). Table 5 summarizes results of paired t test evaluations between comfortable (1.20 _+ . 10m/sec) and fast walking speeds (1.88 + .19m/sec) in a group of five young adult subjects. Table 2: Elderly Versus Young Peak Kinematic Peak Values (°)

Young Elderly (n = 31) (n = 31) Comfortable Comfortable Fast Mean (SD) Mean (SD) Mean (SD) Hip flexion 24.8 (5.0) 26.1 (4,6) 29.6 (5.1) Hip extension -21.0 (4.6) -14.3 (4.1) -14.5 (4.2) Knee flexion loading response 19.2 (5.6) 16.3 (6.0) 21.3 (6.1) Knee extension terminal 1.7 (4.0) 2.2 (4,3) stance 0.6 (2,8) Knee flexion 60.0 (4.5) 57.9 (4.6) 60.1 (4.7) Knee extension terminal 2.7 (4.8) 6.3 (5.6) swing 1.8 (4.2) Ankle plantarflexion loading response -8.0 (3.7) -8.5 (3.0) -7.5 (3.0) Ankle dorsiflexion midstance 8.0 (3.1) 7,7 (3.5) 6.2 (2.6) Ankle plantarflexion -20.9 (6.0) -15,6 (6.3) -16,3 (5.5) 1.8 (4.0) 1.9 (3.7) Ankle dorsiflexion swing 0.6 (3.7) 2.7 (2.7) 4.1 (3.1) Anterior pelvic tilt .03 (2.9)

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SPECIFIC GAIT LIMITATIONS IN HEALTHY ELDERLY, Kerrigan

Table 3: Elderly Versus Young Peak Kinetic Peak Values (n = 31)

Table 4: Significant Age-Associated Kinematic and Kinetic Peak Reductions (p Values)

Young Elderly (n = 31) (n = 31) Comfortable Comfortable Fast Mean (SD) Mean(SD) Mean(SD) Hip flexion moment stance (Nm/kg-m) Hip extension moment (Nm/kg-m) Hip flexion moment swing (Nm/kg-m) Hip power generation loading response (W/ kg-m) Hip power absorption (W/ kg-m) Hip power generation preswing (W/kg-m) Knee extension moment initial contact (Nm/ kg-m) Knee flexion moment midstance (Nm/kg-m) Knee extension moment terminal stance (Nm/ kg-m) Knee flexion moment preswing (Nm/kg-m) Knee power absorption loading response (W/ kg-m) Knee power generation midstance (W/kg-m) Knee power absorption preswing (W/kg-m) Ankle plantarflexion moment (Nm/kg-m) Ankle dorsiflexion moment (Nm/kg-m) Ankle power absorption (W/kg-m) Ankle power generation preswing (W/kg-m)

.46 (.09) -.57 (.15) .12 (.05)

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.77 (.08)

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2.13 (.47)

1.70 (.23)

1,88 (.33)

Briefly, absolute peak hip extension and ankle power generation significantly increased with increased speed, while peak anterior pelvic tilt increased only slightly and absolute peak ankle plantarflexion did not increase significantly with increased speed. DISCUSSION Although other studies have described various kinematic and kinetic attributes of elderly gait, the current study is the first to provide a comprehensive definition and examination of all kinetic and kinematic changes in gait associated with aging that are not merely the result of reduced walking speed. Results may be consistent with potentially limiting hip flexion contractures and weak concentric ankle plantarflexor action affecting overall gait performance. Peak hip extension was reduced in the elderly group at comfortable walking speed, yet it did not significantly increase with faster walking speed. Young adult subjects, on the other hand, increased their hip extension range further with faster walking speed, which has also been reported previously. 1 The reduction in hip extension range in the elderly at both comfortArch Phys Med Rehabil Vol 79, March 1998

Elderly Elderly Elderly Comfortable Fast Versus Comfortable Versus Young Young Versus Comfortable Comfortable Elderly Fast Hip extension (°) Hip flexion moment stance (Nm/kg-m) Knee extension moment initial contact (Nm/ kg-m) Knee flexion moment midstance (Nm/kg-m) Knee flexion moment preswing (Nm/kg-m) Knee power absorption loading response (W/ kg-m) Knee power generation midstance (W/kg-m) Knee power absorption preswing (W/kg-m) Ankle plantarflexion (°) Ankle power generation preswing (W/kg-m) Anterior pelvic tilt (°)

<.001

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* Values for the elderly that were significantly different than in the young, in the same direction, at both speeds.

able and fast speeds is consistent with the prevalence of hip flexion contractures (which prevent the hip from achieving full hyperextension) in the elderly population at large. Reduced peak hip extension in the elderly has not been reported in previous kinematic studies, which could be attributed to a number of factors. Some prior studies have reported only general reductions in overall sagittal plane motion ranges rather than actual peak flexion and extension values. 3,5,7,H Moreover, a number of studies reporting peak flexion and extension values used two-dimensional (2-D) analysis rather than 3-D analysis used here to evaluate joint kinematics. 1,81° Sagittal plane motion using 2-D analysis might be underestimated in the presence of greater hip coronal or transverse motions, which could in fact be greater in the young compared with the elderly population. 22 The observed reduction in hip extension is associated with an overall increase in anterior pelvic tilt (fig 2). Hip flexion contracture produces a shorter maximal contralateral step length. To maintain a reasonable step length with hip flexion contractures, one must compensate with increased anterior pelvic tilt. 23 The pelvis becomes more anteriorly tilted during terminal stance at fast walking speed compared with slow walking speed, presumably to achieve a slightly longer contralateral step length. Because hip flexion contractures limit hip Table 5: Relevant Gait Parameters of Young Subjects at Comfortable and Fast Speeds (n = 5)

Hip extension (o) Ankle plantarflexion (°) Ankle power generation preswing (W/kg-m) Anterior pelvic tilt (o)

Comfortable Speed

Fast Speed

p Value

-19.3 + 5.0 -18.1 _+ 6.3

-22.6 _+ 6.0 -21.2 _+ 5.0

.0080 .1450

2.13 _+ .33 -1.3 ± 4.8

2.96 ± .54 1.7 + 5.4

.0002 .0510

SPECIFIC GAIT LIMITATIONS IN HEALTHY ELDERLY, Kerrigan

hyperextension beyond a given range, to take a longer step with increased walking speed the pelvis must anteriorly tilt further than normal during terminal stance when the hip is maximally hyperextended. An age-associated increase in anterior pelvic tilt has been noted by both Winter s and Judge and colleagues, 6 who attributed this finding to unknown postural changes in the elderly. It may be more plausible, however, to attribute increased anterior pelvic tilt to compensation for hip flexion contractures, considering the reduced hip extension range experienced by this same population. Alternatively, the increased anterior pelvic tilt may be caused by kyphosis and lumbar lordosis, with secondary effects on hip extension. This idea, however, is not consistent with the fact that anterior pelvic tilt increased at faster walking speed while hip extension remained unchanged. Subtle hip flexion contracture in the healthy elderly has not been previously noted with standard clinical or nondynamic testing. The reason for this may be that the Thomas test (the main clinical screening test to assess for hip flexion contracture) can only detect contractures that limit the hip from extending to a neutral position, not subtle changes in hyperextension. 24 Future research might include efforts to improve our current static measurement of hip range of motion. For instance, the same quantitative assessment used to assess dynamic hip range of motion during gait might be implemented in some way to also test for a static hip flexion contracture. Hip flexion contractures may occur in the elderly for a number of reasons. The only activity of daily living performed on a regular basis that hyperextends the hip and thereby stretches the hip flexors is gait, ie, walking or running. 23 We can surmise that a general decline in walking activity in the elderly will cause less regular stretching of the hip flexors, gradually leading to hip flexor tightness and contracture. Although other joints exhibit reduced values as well, these limitations are probably not functionally significant because the full range of motion for those joints is not required during gait. We anticipate that a specific hip flexor stretching exercise program in healthy elderly subjects would improve walking performance overall. Interestingly, although peak hip extension was reduced in the elderly, peak hip extension moment during the same time frame was not significantly reduced compared with young adult subjects. Moreover, peak external hip extension moment was significantly increased at faster walking speed. As hip extension moment directly corresponds to forces that tend to hyperextend the hip, we may conclude that the elderly can stretch their hip flexors with walking just as well as young adult subjects. Thus, walking as an exercise, rather than specific hip flexor stretching exercise, may be sufficient to reverse these contractures and improve walking performance. Clearly, future research to identify and quantitate subtle hip flexion contracture, improve hip flexion contracture with exercise, and correlate this improvement to changes in gait parameters, is warranted. The persistent reduction in both peak ankle plantarflexion and ankle power generation at both walking speeds suggests restricted ankle plantarflexion range, ie, a contracture restricting plantarflexion or reduced concentric action of the ankle plantarflexors. Since normal ankle plantarflexion in gait is only 15 ° to 20 ° and the elderly have only a small reduction in this parameter compared with young adults (approximately 40 ° to 45 ° compared with 35 ° to 40°), 25 an ordinary ankle plantarflexion contracture can be ruled out. Alternatively, elderly subjects may have reduced ankle plantarflexor strength, which is consistent with prior reports that ankle plantarflexor power tested statically is specifically reduced in the elderly and correlates with their reduction in gait speed. 26,27Reduced ankle

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plantar flexor strength was also previously suggested by Winter, 1 and Judge and colleagues. 6 Our findings suggest that the type of reduced ankle plantarflexor strength may be somewhat unusual and deserves further study. The preserved ankle moment observed in the current study indicates that the ankle plantarflexors are sufficiently strong eccentrically to stabilize the ankle as the body moves forward into terminal stance. 21 The reduction in ankle power, on the other hand, is consistent with isolated, reduced concentric ankle plantarflexion action. Perhaps there is some type of dynamic stiffness as a result of intrinsic muscle or soft tissue changes in the ankle plantarflexors, or co-contraction in the antagonistic ankle dorsiflexors, that limits the development of rapid ankle plantar flexion. That concentric ankle plantarflexor action may be specifically reduced agrees with previous studies of strength in the elderly. 28,29 Porter and colleagues 28 found reduced concentric ankle plantarflexor strength in the elderly while eccentric strength in this population was well preserved. Likewise, Thelen and colleagues 29 reported an age-associated decrease in rapid torque development. We must consider another possibility, that reduced ankle plantarflexion range may not represent an impairment but rather a strategy to preserve balance during walking. Conceivably, ankle plantarflexion is purposefully reduced to maintain greater foot-floor contact at terminal stance to broaden the base of support. This possibility, not considered to date, deserves further exploration, including perhaps evaluation of the area of foot-floor contact with a foot pressure-measuring device and/or assessing if this finding persists when using a cane, which theoretically should increase base of support. Probably the best way to sort out if reduced ankle plantarflexion range indeed represents impaired concentric ankle plantarflexion action and not a compensation is to perform an experimental trial of concentric ankle plantarflexor strengthening, emphasizing rapid torque development. Reduced knee extensor or quadricep muscle activity in the elderly may be inferred from reductions observed at comfortable walking speed in peak knee flexion moment at midstance and both peak power absorption at loading response and peak knee power generation at midstance. 21,3° This would be consistent with previous reports of reduced knee extensor strength per static testing in the elderly. 31,32However, all of these parameters are significantly increased at fast walking speed in the elderly and are equivalent to or exceed the young adult reference values. These findings support the notion that the elderly have comparable maximal strength in the quadriceps and are able to use this strength when walking at faster speed. Similarly, the reduced peak hip flexion moment in stance, also reported by Crowinshield, 15 may be interpreted as reduced hip extensor activity; however this parameter also significantly increases at fast walking speed, indicating that subjects do in fact have sufficient maximal strength in the hip extensors. At present, there is no clearly accepted, specific measure of dynamic stability during gait. Percentage of time in double support and step length could be considered general measures of stability, but because these measures are rather nonspecific, it is difficult to conclude the meaningfulness of correlation studies between specific gait parameters and these temporal measures. For instance, it is difficult to determine whether peak hip extension or reduced ankle power are responsible for limiting step length and increasing double support time, or whether reduced hip extension is used as a strategy to maintain balance, thereby reducing step length and double support time. Alteruatively, both could be secondarily related to some other, unknown impairment or strategy. Arch Phys Med Rehabil Vol 79, March 1998

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SPECIFIC GAIT LIMITATIONS IN HEALTHY ELDERLY, Kerrigan

The elderly subjects recruited for this study were healthy, without known musculoskeletal, neurologic, cardiac, or pulmonary diagnoses, and probably well represent the population at large. However, because these subjects were not stratified according to types or amounts of physical activity, it is important to note that for those elderly subjects who exercise regularly, specific age-associated and velocity-independentgait changes found in this study might not be observed. Furthermore, it is possible that the findings we observed might be exaggerated in elderly people who are prone to falls. Falling is commonly associated with activities that require hip extension and ankle plantarflexion, such as walking, climbing stairs, or reaching upward to take an object off of a high shelf. The ability to perform these activities may be improved with specific hip flexor stretching and ankle plantarflexor strengthening exercises. Future studies are needed to understand alterations in the biomechanics of gait in fallers, and to identify appropriate interventions. CONCLUSION Several age-related kinematic and kinetic gait changes were found that did not persist when walking speed was increased. Changes persisting at both comfortable and fast walking speeds were reduced peak hip extension, increased anterior pelvic tilt, and reduced ankle plantartlexion and ankle power generation. These specific findings suggest that gait performance in the elderly may be limited by both subtle hip flexion contracture and ankle plantarflexor concentric weakness. It is possible that the observed gait abnormalities may be exaggerated in elderly people who are prone to falls. Results of the current study should motivate both further exploration of these possible limitations and experimental trials of specific hip flexor stretching and ankle plantarflexor concentric strengthening exercises with the goal to preserve and potentially improve walking performance in the elderly. Acknowledgments: The authors acknowledge Richard Goldstein, PhD for his assistance with statistical design and analysis and Tom Ribando, MS for his technical assistance.

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