Muscle power compensatory mechanisms in below-knee amputee gait

Impairment variables predicting activity limitation in individuals with lower limb amputation

The purpose of this study was to determine whether measures of impairment (i.e., muscle strength, balance), personal factors (i.e., comorbidities, demographic information) and amputation specific variables (i.e., time since amputation, cause of amputation, level of amputation) were able to predict performance on the six-minute walk test, a measure of activity limitation, in individuals with lower limb amputation. A total of 72 individuals with lower limb amputation ranging in age from 21-83 were tested for balance, limb muscle strength and function. Medical comorbidities were recorded and activity limitation was measured using the six-minute walk test. Data were analyzed and multivariate relationships were examined using multiple linear regression. Impairment variables of strength, balance, subject demographics, time since amputation, cause of amputation and level of amputation were all significant predictors and explained 72% of the variance in the outcome variable. Strength of the hip extensors was the strongest predictor, accounting for 30.9% of the total variance. Multiple factors impact six minute walk scores in individuals with lower limb amputation. Impairments in hip strength and balance appear to be the two most significant. The findings of this study support the use of the six-minute walk test to underscore impairments of the musculoskeletal system that can affect ambulation ability in the amputee.

It pays to have a spring in your step

In humans, a large portion of the mechanical work required for walking comes from muscle-tendons crossing the ankle joint. Elastic energy storage and return in the Achilles tendon during each step enhance the efficiency of ankle muscle-tendon mechanical work far beyond what is possible for work performed by knee and hip joint muscle-tendons.

The energy cost for the step-to-step transition in amputee walking

The purpose of this study was to investigate whether the increased energy cost of amputee gait could be accounted for by an increase in the mechanical work dissipated during the step-to-step transition in walking. Eleven transtibial amputees (AMP) and 11 age-matched controls (CO) walked at both comfortable (CWS) and fixed (FWS, 1.3m/s) walking speed, while external mechanical work of each separate leg and metabolic energy consumption were measured. At FWS the metabolic energy consumption (E(met)) was significantly higher in AMP compared to CO (3.34 Jkg(-1)s(-1) vs. 2.73 Jkg(-1)s(-1)). At CWS, no difference in energy consumption was found (3.56 Jkg(-1)s(-1) vs. 3.58 Jkg(-1)s(-1)) but CWS was significantly lower in AMP compared to CO (1.35 ms(-1) vs. 1.52 ms(-1)). In conjunction with the higher E(met) at FWS, the negative work generated by the intact leading leg for the step-to-step transition in double support was significantly higher for AMP than CO at FWS. A moderate though significant correlation was found between negative mechanical power generated during the step-to-step transition and metabolic power (CWS: r=-0.56, p=0.007; FWS: r=-0.50, p=0.019). Despite the difference in negative work during the step-to-step transition, the total absolute mechanical work over a stride did not differ between groups. This could possibly be attributed to exchange of internal positive and negative work during single support, which remains unnoticed in the external work calculations. It was concluded that the increased mechanical work for the step-to-step transition from prosthetic to intact limb contributes to the increased metabolic energy cost of amputee walking.

Gait patterns in transtibial amputee fallers vs. non-fallers: biomechanical differences during level walking

Transtibial amputees are at an increased risk of falling compared to age-matched, able-bodied individuals. The aim of this study was to compare the gait patterns of recent amputee fallers vs. non-fallers during level walking by investigating joint kinematics, kinetics and variability of temporal-spatial parameters. Eleven participants (fallers=6; non-fallers=5) walked along a 10-m walkway at their self-selected pace while three-dimensional kinematic and kinetic data were collected. The fallers had a significantly greater first peak vertical GRF (p=0.01) and load rate on the prosthetic limb than the non-fallers (p=0.03). Joint range of motion was similar between the two groups. Joint moment profiles were similar for the ankle and hip, with more noticeable differences at the knee. On the intact limb, the fallers also showed significantly smaller A1 and larger H2 power bursts and greater variability of swing time duration compared to the non-fallers. The non-fallers had a smaller load rate and knee moment that remained extensor suggesting they could make compensatory adjustments to maintain stability on the prosthetic side by modifying muscular demands of the knee extensors. This research suggests that falls prevention and prosthetic rehabilitation programmes should focus on improving knee muscle strength of the prosthetic limb, and eccentric ankle and hip strength of the intact limb, to improve stability and progression, particularly during weight transfer onto single support of the prosthetic limb.

Compensatory mechanism involving the knee joint of the intact limb during gait in unilateral below-knee amputees

This study evaluated the asymmetry of knee kinetics during uncomfortable gait induced by prosthesis misalignment to further demonstrate the compensatory function of the knee joint of the intact limb during gait. Three-dimensional gait analysis including knee kinematics and kinetics at the beginning of stance phase was conducted in 15 healthy subjects and 17 unilateral trans-tibial amputees (TTA) walking at self-selected speed in three conditions of prosthetic alignment: initial alignment (IA); initial alignment altered either by 6 degrees of internal rotation (IR) or by 6 degrees of external rotation (ER) applied on the pylon. Patients reported best comfort of gait in IA condition and discomfort mainly in IR condition. Maximum knee flexion and knee total work at power phases K0-K2 were significantly higher in intact limbs compared to prosthetic and control limbs. In intact limbs, these variables had significantly higher values (+10-35%, p<0.05) in IR condition than IA condition whereas these were not altered across conditions in prosthetic limbs. In trans-tibial amputees, inducing uncomfortable gait by internally rotating the prosthetic foot did not alter the knee kinetics of the prosthetic limb, which suggests a protective mechanism. Knee kinetics of the intact limb did alter, which suggests a compensatory mechanism.

Effects of cadence on energy generation and absorption at lower extremity joints during gait

BACKGROUND

Information regarding kinetic changes associated with walking speed is important for identifying alterations in locomotor disorders caused by pathological processes, as opposed to those arising solely from altered speeds.

METHODS

Fourteen healthy subjects were assessed walking at both natural and imposed cadences of 60, 80, and 120 steps/min. A 3D motion analysis system, force platforms, and related software were used to obtain kinematic and kinetic data. Net joint powers were calculated across cycles and the area under the positive and negative phases of the power curves provided the mechanical work generated and absorbed at the hip, knee, and ankle. The relative contributions to the total positive and negative work across the four cadences were calculated for each joint. ANOVAs followed by planned contrasts were used to assess the effects of laterality, joint, and cadence.

FINDINGS

Power and mechanical work, as well as the contributions of individual joints to the total energy generated and absorbed, were shown to be influenced by walking cadence, independent of laterality. The ankle, knee, and hip contributions to the total limb generation and absorption at the lowest cadence were 53%, 21%, and 26%, and at the highest cadence, the corresponding values were 34%, 33%, and 33%, respectively.

INTERPRETATION

Power and mechanical work, as well as the contributions of individual joints to the total energy generated and absorbed, were shown to be influenced by the walking cadence, independent of laterality. These findings will be helpful for identifying walking strategies and adaptations in populations with gait disorders.

Ipsilateral total hip arthroplasty in a dysvascular below-knee amputee for advanced hip osteoarthritis: A case report and review of the literature

This retrospective file review outlines a case study of an 84 year-old man with a transtibial amputation for vascular disease who underwent an ipsilateral total hip replacement (THR). The question being addressed was how surgical techniques, rehabilitation processes and outcomes of joint arthroplasty would need to vary in a case of an ipsilateral dysvascular amputees. The surgery and associated rehabilitation was undertaken for groin pain, falls and reduced mobility due to mechanical osteoarthritis of the hip. The surgical technique and post-operative multidisciplinary rehabilitation is described in detail. Information on exercise regimes, length of stay and follow-up data on function, driving and pain management is presented. The literature is reviewed and all known cases of THR in amputees as well as data on survival of dysvascular amputees is presented. In light of advances in secondary prevention of vascular disease and cardiovascular surgical techniques, amputees with vascular disease may be living longer than they were 20 years ago. They may be beginning to experience the issues associated with aging such as osteoarthritis of the large joints. This case review and others in the literature may suggest that survival rates for vascular amputees be reviewed.

Robotic gait trainer in water: development of an underwater gait-training orthosis

PURPOSE

To develop a robotic gait trainer that can be used in water (RGTW) and achieve repetitive physiological gait patterns to improve the movement dysfunctions.

METHOD

The RGTW is a hip-knee-ankle-foot orthosis with pneumatic actuators; the control software was developed on the basis of the angular motions of the hip and knee joint of a healthy subject as he walked in water. Three-dimensional motions and electromyographic (EMG) activities were recorded in nine healthy subjects to evaluate the efficacy of using the RGTW while walking on a treadmill in water.

RESULTS

The device could preserve the angular displacement patterns of the hip and knee and foot trajectories under all experimental conditions. The tibialis anterior EMG activities in the late swing phase and the biceps femoris throughout the stance phase were reduced whose joint torques were assisted by the RGTW while walking on a treadmill in water.

CONCLUSION

Using the RGTW could expect not only the effect of the hydrotherapy but also the standard treadmill gait training, in particular, and may be particularly effective for treating individuals with hip joint movement dysfunction.

[Isometric hip muscle strength in posttraumatic below-knee amputees]

BACKGROUND/AIM

Traumas and war injuries, next to chronic occlusive artery disease and diabetes mellitus-derived complications, are the most frequent cause of the lower limbs amputation. They affect mostly younger population that need a higher level of activities as compared with the elderly. Medical rehabilitation is very significant for the muscle performance improvement in this population providing their social reintegration. The aim of this study was to investigate the effect of below-knee amputation on the hip isometric muscle strength and effect of rehabilitation on improvement of hip muscle strength in below-knee amputees, secondary to war wounding.

METHODS

Forty below-knee amputees (after war wounding), average age 35.6 +/- 10.6 years, that were included in primary rehabilitation program with prosthetics, were examined. Objective parameters were used to evaluate therapeutical effects. Isometric muscle strength of hip flexors, extensors, abductors and adductors was measured by dynamometer and expressed in Newton (N) at admission, control and discharge for each patient. Average length of the treatment was 51 +/- 34.1 days.

RESULTS

For isometric hip flexors (t = -1.99346, p < 0.05), extensors (t = -4.629073, p < 0.001), abductors (t = -4.9408, p < 0.001) and adductors (t = -2.00228, p < 0.05), muscle strength was significantly less on the amputated than on nonamputated side. The highest differences in muscle strength between amputated and nonamputated limbs were noted for hip abductors (26.6%) and extensors (23.3%). There was significant improvement of mean values of strength for all examined hip muscles after rehabilitation and prosthetics for both legs in comparison to beginning of the therapy. The hip abductor on the amputated side was for 19.4% weaker after rehabilitation in comparison to the non-amputated limb.

CONCLUSION

Decreases of isometric muscle strength in all examined hip muscles were observed, more in the amputated limb. Rehabilitation with prosthetics is a successful method for improving isometric hip muscle strength on the both, amputated and non-amputated limbs in war wounded below-knee amputees.

[Muscles of the below-knee amputees]

OBJECTIVE

The objective of this article is to review anatomical, histological and physiological muscle changes following below-knee amputation.

MATERIALS AND METHODS

We searched the PubMed and Reedoc databases for studies evaluating modifications of the below-knee stump and changes over time in its anatomy, volume and histology. We also looked at postamputation modifications in gait and balance.

RESULTS

Below-knee amputees show muscular atrophy on both the amputated side and nonamputated side, with fewer and smaller muscle fibres (particularly slow-twitch fibres). This amyotrophy varies in magnitude and distribution and can reach about 25% for the quadriceps (predominantly on the medial side), but is nonsignificant for the hamstrings. This amyotrophy results from the anatomical consequences of the surgical act. The loss of one or more of a muscle's insertions or reimplantation into a nonphysiological site prompts greater atrophy. Changes in muscle activation patterns also lead to atrophy. The hamstrings replace the triceps as the main muscles for propulsion and the remaining stump muscles contract so as to ensure a good fit with the prosthesis. The below-knee amputee must adapt to a new muscular state: gait symmetry is altered, energy expenditure for walking is higher and training is needed in order to achieve optimal balance control.

Muscle adaptation patterns of children with a trans-tibial amputation during walking

BACKGROUND

Many studies have shown that trans-tibial amputation involves modifications of resultant muscle patterns during gait. However, these experiments did not estimate the contribution of simultaneous agonist and antagonist muscle action (co-contraction) during gait tasks. Diminution of co-contraction could create joint instability and, thus, change joint integrity, which is particularly important in the etiology of degenerative diseases, such as osteoarthritis, present at the knees of amputated limbs, and particularly in non-amputated limbs. The purpose of this study was to determine if there is any difference in the production of co-contraction about the knee between able-bodied children and children with a trans-tibial amputation during gait.

METHODS

Six children with a trans-tibial amputation vs. six able-bodied children paired for gender, age, weight and height participated in this study. Four one-way ANOVAs (P<0.05) were used to observe differences in resultant, agonist and antagonist moments, power, and co-contraction index during different phases of gait between able-bodied children limbs, the amputated and the non-amputated limbs of children with trans-tibial amputation.

FINDINGS

Children with a trans-tibial amputation modified muscle patterns at their amputated limb and produced smaller co-contraction (P<0.05) during single limb support, for both the non-amputated and amputated limbs when compared to able-bodied children.

INTERPRETATION

These results suggest that children with a trans-tibial amputation altered their muscle patterns to perform locomotion. These changes produced a diminution of co-contraction during single limb support for both the amputated and non-amputated limbs and, thus, could create joint instability.

Gait symmetry and walking speed analysis following lower-extremity trauma

BACKGROUND AND PURPOSE

Gait has been shown to be a major determining factor of function following limb-salvage surgery. However, little is known regarding the measures associated with gait recovery for this patient population. The purpose of this study was to identify clinical measures associated with impaired walking speed and gait asymmetry in patients with lower-extremity reconstruction.

SUBJECTS

Study subjects were 381 patients from the Lower Extremity Assessment Project (LEAP) who had undergone reconstruction following severe lower-extremity trauma.

METHODS

The LEAP study was a longitudinal study of outcomes following lower-extremity reconstruction. The present study used 24-month clinical follow-up data. A combined outcome measure of reduced walking speed and gait deviation was chosen to provide a comprehensive measure of impaired physical mobility.

RESULTS

The most significant clinical factors associated with decreased walking speed and gait deviation were impaired ankle plantar-flexion range of motion, knee flexion strength, and a nonreciprocal stair-climbing pattern.

DISCUSSION AND CONCLUSION

The findings provide clinicians with specific clinical measures associated with functional recovery in patients with lower-limb reconstruction. These measures, in turn, can be considered to inform treatment decision making and to prioritize interventions.

Mechanical energetic contributions from individual muscles and elastic prosthetic feet during symmetric unilateral transtibial amputee walking: a theoretical study

Energy storage and return (ESAR) foot-ankle prostheses have been developed in an effort to improve gait performance in lower-limb amputees. However, little is known about their effectiveness in providing the body segment mechanical energetics normally provided by the ankle muscles. The objective of this theoretical study was to use muscle-actuated forward dynamics simulations of unilateral transtibial amputee and non-amputee walking to identify the contributions of ESAR prostheses to trunk support, forward propulsion and leg swing initiation and how individual muscles must compensate in order to produce a normal, symmetric gait pattern. The simulation analysis revealed the ESAR prosthesis provided the necessary trunk support, but it could not provide the net trunk forward propulsion normally provided by the plantar flexors and leg swing initiation normally provided by the biarticular gastrocnemius. To compensate, the residual leg gluteus maximus and rectus femoris delivered increased energy to the trunk for forward propulsion in early stance and late stance into pre-swing, respectively, while the residual iliopsoas delivered increased energy to the leg in pre- and early swing to help initiate swing. In the intact leg, the soleus, gluteus maximus and rectus femoris delivered increased energy to the trunk for forward propulsion in the first half of stance, while the iliopsoas increased the leg energy it delivered in pre- and early swing. Thus, the energy stored and released by the ESAR prosthesis combined with these muscle compensations was able to produce a normal, symmetric gait pattern, although various neuromuscular and musculoskeletal constraints may make such a pattern non-optimal.

Arm coordination symmetry and breathing effect in front crawl

This study analysed the relationships among arm coordination symmetry, motor laterality and breathing laterality during a 100-m front crawl, as a function of expertise. Ten elite swimmers (G1), 10 mid-level swimmers (G2), and 8 non-expert swimmers (G3) composed three skill groups, which were distinguished by velocity, stroke rate, stroke length, breathing frequency (BF) and the mean number of strokes between two breaths - the stroke breath (SB) - over a 100-m front crawl. Four stroke phases were identified by video analysis (catch, pull, push and recovery) and the index of coordination (IdC) measured the lag time between the propulsive phases of the two arms. The three modes of coordination are catch-up (IdC<0%), opposition (IdC=0%) and superposition (IdC>0%). The IdC was established as the mean of IdC1 and IdC2, which measured the lag time between the propulsive phases of the left and right arms, respectively. The coordination symmetry was analysed by comparing IdC1 and IdC2, and the breathing effect was studied by distinguishing IdC1 (and IdC2) with and without breathing. Motor laterality was determined by an adaptation of the Edinburgh Handedness Inventory. Breathing laterality was determined by a questionnaire and observation during the 100-m trial. Most of the front crawl swimmers showed asymmetric arm coordination, with propulsive discontinuity on one side and propulsive superposition on the other. This asymmetry was most often related to breathing laterality (a preferential breathing side for a unilateral breathing pattern) and motor laterality (arm dominance), with different profiles noted. More than the breathing laterality itself, the breathing actions of the non-expert swimmers amplified their asymmetric coordination on the breathing side. Conversely, the elite swimmers, who had higher and more stable spatial-temporal parameters (velocity and stroke lengths), a high coordination value (IdC) and lower breathing frequency (BF), managed their race better than the less proficient swimmers and their asymmetric arm coordination was not disturbed by breathing actions. By determining the dominant arm and the preferential breathing side, the coach can obtain a swimmer profile that allows both coach and swimmer to better understand and respond to excessive coordination asymmetry.

Functional roles of lower-limb joint moments while walking in water

OBJECTIVE

To clarify the functional roles of lower-limb joint moments and their contribution to support and propulsion tasks while walking in water compared with that on land.

DESIGN

Sixteen healthy, young subjects walked on land and in water at several different speeds with and without additional loads.

BACKGROUND

Walking in water is a major rehabilitation therapy for patients with orthopedic disorders. However, the functional role of lower-limb joint moments while walking in water is still unclear.

METHODS

Kinematics, electromyographic activities in biceps femoris and gluteus maximums, and ground reaction forces were measured under the following conditions: walking on land and in water at a self-determined pace, slow walking on land, and fast walking in water with or without additional loads (8 kg). The hip, knee, and ankle joint moments were calculated by inverse dynamics.

RESULTS

The contribution of the walking speed increased the hip extension moment, and the additional weight increased the ankle plantar flexion and knee extension moment.

CONCLUSIONS

The major functional role was different in each lower-limb joint muscle. That of the muscle group in the ankle is to support the body against gravity, and that of the muscle group involved in hip extension is to contribute to propulsion. In addition, walking in water not only reduced the joint moments but also completely changed the inter-joint coordination.

RELEVANCE

It is of value for clinicians to be aware that the greater the viscosity of water produces a greater load on the hip joint when fast walking in water.

Strength and endurance training of an individual with left upper and lower limb amputations

PURPOSE

The purpose of this article is to describe the development of a strength and endurance training programme designed to prepare an individual with a left glenohumeral disarticulation and transtibial amputation for a bike trip across the USA.

METHOD

The subject was scheduled for training three times per week over a two-month period followed by two times per week for an additional two months. Training consisted of a resistance training circuit using variable resistance machines, cycling using a recumbent stationary bike, and core stability training using stability ball exercises. Changes in strength were assessed using 10 RM tests on the resistance machines and changes in peak VO(2) were monitored utilizing the Cosmed K4b pulmonary function tester.

RESULTS

The subject demonstrated a 30.3% gain in peak VO(2). The subject's 10 RM for left single limb leg press increased 36.8% and gains of at least 7.7% were seen for all other muscle groups tested.

CONCLUSION

The strength and endurance training programme adapted to compensate for this subject's limb losses was effective in increasing both strength and peak VO(2). Adapting exercise programmes to compensate for limb loss may allow individuals with amputations to participate in physically challenging activities that otherwise may not be available to them.

Postural and movement adaptations by individuals with a unilateral below-knee amputation during gait initiation

The present study examined the compensatory strategies adopted by individuals with a unilateral below-knee amputation (BKA) during gait initiation. Eleven individuals with a unilateral BKA and 11 able-bodied subjects initiated gait at three step length conditions (+0, +25 and +50% of preferred step length). A lead-limb condition was also introduced, such that all participants were required to initiate gait with both their left and right limbs. For all step length and lead-limb conditions, it was found that individuals with a unilateral BKA required more time to initiate gait, as compared with the able-bodied. This increase in movement duration was attributed to the stability and movement limitations of the prosthetic limb. On the other hand, by prolonging the task duration, these individuals were also able to employ a 'horizontal impulse' strategy, whereby they could create a similar magnitude of horizontal impulse as the able-bodied without the need to apply a large magnitude of peak antero-posterior (A-P) force.

Local or global asymmetry in gait of people without impairments

Using two consecutive gait cycles, simultaneous and bilateral kinetic gait data, the main objectives of this study were (a) to identify the main functional roles of ankle, knee and hip extensors/flexors, and (b) to determine whether the action taken by these muscle groups appears to be symmetric or not. Gait of our able-bodied subjects appears to be asymmetric with significant differences noted between each two corresponding peak muscle moment values. Using principal component analysis (PCA) as a curve structure detection method, task discrepancies were recognized when comparisons were made between each two corresponding representative moment curves at each joint (local asymmetry). Muscle moment behaved symmetrically when the right limb representative curve was compared to its corresponding principal component (PC) at the contralateral limb. Gait of able-bodied subjects appears to be symmetric, while control and propulsion were recognized as two major roles of the extensors and flexors (global gait asymmetry). Symmetrical behavior of the lower limbs should be considered a consequence of local asymmetry which indicates different levels of within and between muscle activities developed at each joint during gait cycles.

Continuous curve registration as an intertrial gait variability reduction technique

Timing in peak values shifts slightly between gait trials. When gait data are averaged, part of the standard deviation could be associated with this intertrial variability unless normalization is carried out beforehand. The objective of this study was to determine how continuous curve registration, an alignment technique, can reduce intersubject variability in gait data without altering the original curve characteristics. Gait data were obtained by means of a four-camera high-speed video system synchronized to a force plate. The data for 60 gait trials were collected from 20 young, healthy subjects. Curve registration was applied to hip angular displacement, net moment, and power curves generated in the sagittal plane. Following registration, the peak values increased by an average of 1.2% (0.11 +/- 0.26 degrees) for angular displacement, and by 11.2% (0.11 +/- 0.09 W/kg) for power, while there were no changes for moments. First and second derivatives of the unregistered and registered curves did not display significant differences, and the harmonics were barely affected. Continuous curve registration would thus be an appropriate technique for application prior to any statistical analysis using able-bodied gait patterns.

Relationship between ankle frontal muscle powers and three-d gait patterns

OBJECTIVE

This study was undertaken to demonstrate that the ankle frontal muscle power absorption and generation at push-off are related to the foot's initial position at heel-strike with respect to the body center of mass.

DESIGN

Nineteen able-bodied male subjects participated in this study and were divided into two groups according to ankle frontal plane power generation or absorption at push-off.

RESULTS

At heel-strike, the group that absorbed had a center of pressure that was located on average 25% more anteriorly and 36% more laterally to the body center of mass. Moreover, at push-off, the center of pressure was closer (26%) to the center of mass than in the generating group. The absorbing group compensated by increasing their sagittal plane hip energy by 30% to pull the lower limb forward and their knee power absorption by 47% to slow down the leg before the subsequent heel-strike.

CONCLUSIONS

The foot's initial position at heel-strike explains in part the ankle frontal power generation or absorption at push-off. Increasing hip and knee sagittal joint powers and mechanical energies were the main contributors in compensating and providing a broader base of support and frontal plane ankle power absorption.

Functional roles of ankle and hip sagittal muscle moments in able-bodied gait

OBJECTIVE

The main objectives of this study on able-bodied gait were (a) to identify the main functions of the ankle and hip muscle moments and their contribution to support and propulsion tasks, and (b) to illustrate the interaction between the ankle and hip moment activities.

DESIGN

Twenty young, able-bodied male subjects walked along a 13 m path at a freely chosen speed.

BACKGROUND

Functional contributions of the ankle and hip muscles and their interactions in achieving support and propulsion tasks during gait are still subject to controversy.

METHODS

Principal component analysis was applied as a curve structure detection method to identify the main functional characteristics of the ankle and hip muscle moments. The first two principal components which contained over 70% and 85%, respectively, of the information in the ankle and hip moment curves revealed their functional tasks. Ankle versus hip moment plots was used to illustrate the interactions between muscles acting at the hip and ankle in the sagittal plane. Correlation coefficient and covariance calculations quantified the interaction between the ankle and hip moments.

RESULTS

The first principal component revealed that the main role of the ankle and hip is to keep the body from collapsing. The second principal component is associated with the functional contribution of both ankle plantarflexors and hip flexors during the propulsion phase (50-60% of the gait cycle). High coordination (r=0.82) between the ankle and hip moments was observed.

CONCLUSION

Maintaining body support against gravity was identified as the first functional task of the ankle plantarflexors and hip extensors, while contribution to propulsion was recognised as the second major role for the ankle plantarflexors and hip flexors.

RELEVANCE

Identifying the main roles of the muscles acting at the hip and ankle during able-bodied walking provides better insight into how pathological gait should be evaluated.