Walking patterns change rapidly following asymmetrical lower extremity loading

Classifying Changes in Amputee Gait following Physiotherapy Using Machine Learning and Continuous Inertial Sensor Signals

Wearable sensors allow for the objective analysis of gait and motion both in and outside the clinical setting. However, it remains a challenge to apply such systems to highly diverse patient populations, including individuals with lower-limb amputations (LLA) that present with unique gait deviations and rehabilitation goals. This paper presents the development of a novel method using continuous gyroscope data from a single inertial sensor for person-specific classification of gait changes from a physiotherapist-led gait training session. Gyroscope data at the thigh were collected using a wearable gait analysis system for five LLA before, during, and after completing a gait training session. Data from able-bodied participants receiving no intervention were also collected. Models using dynamic time warping (DTW) and Euclidean distance in combination with the nearest neighbor classifier were applied to the gyroscope data to classify the pre- and post-training gait. The model achieved an accuracy of 98.65% ± 0.69 (Euclidean) and 98.98% ± 0.83 (DTW) on pre-training and 95.45% ± 6.20 (Euclidean) and 94.18% ± 5.77 (DTW) on post-training data across the participants whose gait changed significantly during their session. This study provides preliminary evidence that continuous angular velocity data from a single gyroscope could be used to assess changes in amputee gait. This supports future research and the development of wearable gait analysis and feedback systems that are adaptable to a broad range of mobility impairments.

Dynamic visual acuity during asymmetric walking

Necessary for effective ambulation, head stability affords optimal conditions for the perception of visual information during dynamic tasks. This maintenance of head-in-space equilibrium is achieved, in part, by the attenuation of the high frequency impact shock resulting from ground contact. While a great deal of experimentation has been done on the matter during steady state locomotion, little is known about how locomotor asymmetry might affect head stability or dynamic visual acuity. In this study, fifteen participants walked on a split-belt treadmill while verbally reporting the orientation of a randomized Landolt-C optotype that was projected at heel strike. Participants were exposed to baseline, adaptation, and washout conditions, as characterized by belt speed ratios of 1:1, 1:3, and 1:1, respectively. Step length asymmetry, shock attenuation, high and low frequency head signal power, and dynamic visual acuity were averaged across the first and last fifty strides of each condition. Across the first fifty strides, step length asymmetry was significantly greater during adaptation than during baseline (p < 0.001; d = 2.442), and shock attenuation was significantly lower during adaptation than during baseline (p = 0.041; d = -0.679). High frequency head signal power was significantly greater during adaptation than during baseline (p < 0.001; d = -1.227), indicating a reduction in head stability. While dynamic visual acuity was not significantly lower during adaptation than during baseline (p = 0.052), a moderate effect size suggests a decrease in the measure between the two conditions (d = 0.653). Across the last fifty strides, many of the decrements observed between the baseline and adaptation conditions were greatly reduced. The results of this study indicate that the locomotor asymmetry imposed by the split-belt treadmill during early adaptation might lead to moderate decrements in shock attenuation, head stability, and dynamic visual acuity. Moreover, the relative reduction in magnitude of these decrements across the last fifty strides underscores the adaptive nature of the locomotor and visuomotor systems.

Lower back kinetic demands during induced lower limb gait asymmetries

BACKGROUND

Gait asymmetries are common in many clinical populations (e.g., amputation, injury, or deformities) and are associated with a high incidence of lower back pain. Despite this high incidence, the impact of gait asymmetries on lower back kinetic demands are not well characterized due to experimental limitations in these clinical populations. Therefore, we artificially and safely induced gait asymmetry during walking in healthy able-bodied participants to examine lower back kinetic demands compared to their normal gait.

RESEARCH QUESTION

Are lower back kinetic demands different during artificially induced asymmetries than those during normal gait?

METHODS

L5/S1 vertebral joint kinetics and trunk muscle forces were estimated during gait in twelve healthy men and women with a musculoskeletal lower back model that uniquely incorporated participant-specific responses using an EMG optimization approach. Five walking conditions were conducted on a force-measuring treadmill, including normal unperturbed "symmetrical" gait, and asymmetrical gait induced by unilaterally altering leg mass, leg length, and ankle joint motion in various combinations. Gait symmetry index and lower back kinetics were compared with repeated-measures ANOVAs and post hoc tests (α = .05).

RESULTS

The perturbations were successful in producing different degrees of step length and stance time gait asymmetries (p < .01). However, lower back kinetic demands associated with asymmetrical gait were similar to, or only moderately different from normal walking for most conditions despite the observed asymmetries.

SIGNIFICANCE

Our findings indicate that the high incidence of lower back pain often associated with gait asymmetries may not be a direct effect of increased lower back demands. If biomechanical demands are responsible for the high incidence of lower back pain in such populations, daily tasks besides walking may be responsible and warrant further investigation.

The Short-Term Effects of Rhythmic Vibrotactile and Auditory Biofeedback on the Gait of Individuals After Weight-Induced Asymmetry

BACKGROUND

Biofeedback (BFB), the practice of providing real-time sensory feedback has been shown to improve gait rehabilitation outcomes. BFB training through rhythmic stimulation has the potential to improve spatiotemporal gait asymmetries while minimizing cognitive load by encouraging a synchronization between the user's gait cycle and an external rhythm.

OBJECTIVE

The purpose of this work was to evaluate if rhythmic stimulation can improve the stance time symmetry ratio (STSR) and to compare vibrotactile to auditory stimulation. Gait parameters including velocity, cadence, stride length, double support time, and step length symmetry, were also examined.

METHODOLOGY

An experimental rhythmic stimulation system was developed, and twelve healthy adults (5 males), age 28.42 ± 10.93 years, were recruited to participate in walking trials. A unilateral ankle weight was used to induce a gait asymmetry to simulate asymmetry as commonly exhibited by individuals with lower limb amputation and other clinical disorders. Four conditions were evaluated: 1) No ankle weight baseline, 2) ankle weight without rhythmic stimulation, 3) ankle weight + rhythmic vibrotactile stimulation (RVS) using alternating motors and 4) ankle weight + rhythmic auditory stimulation (RAS) using a singletone metronome at the participant's self-selected cadence.

FINDINGS

As expected the STSR became significantly more asymmetrical with the ankle weight (i.e. induced asymmetry condition). STSR improved significantly with RVS and RAS when compared to the ankle weight without rhythmic stimulation. Cadence also significantly improved with RVS and RAS compared to ankle weight without rhythmic stimulation. With the exception of double support time, the other gait parameters were unchanged from the ankle weight condition. There were no statistically significant differences between RVS and RAS.

CONCLUSION

This study found that rhythmic stimulation can improve the STSR when an asymmetry is induced. Moreover, RVS is at least as effective as auditory stimulation in improving STSR in healthy adults with an induced gait asymmetry. Future work should be extended to populations with mobility impairments and outside of laboratory settings.

Ankle resistance with a unilateral soft exosuit increases plantarflexor effort during pushoff in unimpaired individuals

Background

Ankle-targeting resistance training for improving plantarflexion function during walking increases rehabilitation intensity, an important factor for motor recovery after stroke. However, understanding of the effects of resisting plantarflexion during stance on joint kinetics and muscle activity—key outcomes in evaluating its potential value in rehabilitation—remains limited. This initial study uses a unilateral exosuit that resists plantarflexion during mid-late stance in unimpaired individuals to test the hypotheses that when plantarflexion is resisted, individuals would (1) increase plantarflexor ankle torque and muscle activity locally at the resisted ipsilateral ankle, but (2) at higher forces, exhibit a generalized response that also uses the unresisted joints and limb. Further, we expected (3) short-term retention into gait immediately after removal of resistance.

Methods

Ten healthy young adults walked at 1.25 m s⁻¹ for four 10-min discrete bouts, each comprising baseline, exposure to active exosuit-applied resistance, and post-active sections. In each bout, a different force magnitude was applied based on individual baseline ankle torques. The peak resistance torque applied by the exosuit was 0.13 ± 0.01, 0.19 ± 0.01, 0.26 ± 0.02, and 0.32 ± 0.02 N m kg⁻¹, in the LOW, MED, HIGH, and MAX bouts, respectively.

Results

(1) Across all bouts, participants increased peak ipsilateral biological ankle torque by 0.13–0.25 N m kg⁻¹ (p < 0.001) during exosuit-applied resistance compared to corresponding baselines. Additionally, ipsilateral soleus activity during stance increased by 5.4–11.3% (p < 0.05) in all but the LOW bout. (2) In the HIGH and MAX bouts, vertical ground reaction force decreased on the ipsilateral limb while increasing on the contralateral limb (p < 0.01). Secondary analysis found that the force magnitude that maximized increases in biological ankle torque without significant changes in limb loading varied by subject. (3) Finally, peak ipsilateral plantarflexion angle increased significantly during post-exposure in the intermediate HIGH resistance bout (p < 0.05), which corresponded to the greatest average increase in soleus activity (p > 0.10).

Conclusions

Targeted resistance of ankle plantarflexion during stance by an exosuit consistently increased local ipsilateral plantarflexor effort during active resistance, but force magnitude will be an important parameter to tune for minimizing the involvement of the unresisted joints and limb during training.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12984-021-00966-5.

Perceptions of an over-ground induced temporal gait asymmetry by healthy young adults

Nearly 60% of individuals with stroke walk with temporal gait asymmetry (TGA; a phase inequality between the legs during gait). About half of individuals with TGA are unable to correctly identify the presence or direction of their asymmetry. If patients are unable to perceive their gait errors, it will be harder to correct them to improve their gait pattern. Perception of gait pattern error may be affected by the stroke itself; therefore, the objectives of this study were to determine how the gait of neurotypical individuals changes with an induced temporal asymmetry, and how perception of that TGA compares to actual asymmetry both before and after 15-min of exposure to the induced asymmetry. After baseline symmetry (measured as symmetry index (SI)) was assessed with a pressure sensitive mat, participants (n = 29) walked for 15 min over-ground with cuff weights (7.5% of body weight) on their non-dominant leg to induce TGA. Presence, direction, and magnitude of TGA was measured at five time points: 1) baseline, 2) immediately after unilateral loading (early adaptation (EA)), 3) at the end of 15 min of walking (late adaptation (LA)), 4) immediately after load removal (early deadaptation (EDA)), and 5) after the participant indicated that their gait had returned to baseline symmetry (late deadaptation (LDA). Presence, direction, and magnitude of perceived TGA was measured by self-report. Measured and perceived TGA changes over time were assessed with separate one-way repeated measures analyses of variance. Agreement between measured and perceived TGA was assessed. During EA, all participants walked asymmetrically, spending more time on the non-loaded limb compared to baseline (-12.67 [95%CI -14.56, -10.78], p < 0.0001). All but one participant perceived this TGA, however only fifteen (52%) correctly perceived both TGA presence and direction. At LA, the group remained asymmetric (-9.22 [95%CI -11.32, -7.12], p < 0.0001), but only 9 participants (31%) correctly perceived both the presence and direction of their TGA. Visual inspection of the data at each time point revealed most participants perceived TGA magnitude as greater than actual TGA. Overall, we find that TGA can be induced and maintained in neurotypical young adults. Perception of TGA direction is inaccurate and perception of TGA magnitude is grossly overestimated. Perceptions of TGA do not improve after a period of exposure to the new walking pattern. These preliminary findings indicate that accurately perceiving an altered gait pattern is a difficult task even for healthy young adults.

Locomotor skill acquisition in virtual reality shows sustained transfer to the real world

Background

Virtual reality (VR) is a potentially promising tool for enhancing real-world locomotion in individuals with mobility impairment through its ability to provide personalized performance feedback and simulate real-world challenges. However, it is unknown whether novel locomotor skills learned in VR show sustained transfer to the real world. Here, as an initial step towards developing a VR-based clinical intervention, we study how young adults learn and transfer a treadmill-based virtual obstacle negotiation skill to the real world.

Methods

On Day 1, participants crossed virtual obstacles while walking on a treadmill, with the instruction to minimize foot clearance during obstacle crossing. Gradual changes in performance during training were fit via non-linear mixed effect models. Immediate transfer was measured by foot clearance during physical obstacle crossing while walking over-ground. Retention of the obstacle negotiation skill in VR and retention of over-ground transfer were assessed after 24 h.

Results

On Day 1, participants systematically reduced foot clearance throughout practice by an average of 5 cm (SD 4 cm) and transferred 3 cm (SD 1 cm) of this reduction to over-ground walking. The acquired reduction in foot clearance was also retained after 24 h in VR and over-ground. There was only a small, but significant 0.8 cm increase in foot clearance in VR and no significant increase in clearance over-ground on Day 2. Moreover, individual differences in final performance at the end of practice on Day 1 predicted retention both in VR and in the real environment.

Conclusions

Overall, our results support the use of VR for locomotor training as skills learned in a virtual environment readily transfer to real-world locomotion. Future work is needed to determine if VR-based locomotor training leads to sustained transfer in clinical populations with mobility impairments, such as individuals with Parkinson’s disease and stroke survivors.

The biomechanical response of persons with transfemoral amputation to variations in prosthetic knee alignment during level walking

Prosthetic alignment is an important factor in the overall fit and performance of a lower-limb prosthesis. However, the association between prosthetic alignment and control strategies used by persons with transfemoral amputation to coordinate the movement of a passive prosthetic knee is poorly understood. This study investigated the biomechanical response of persons with transfemoral amputation to systematic perturbations in knee joint alignment during a level walking task. Quantitative gait data were collected for three alignment conditions: bench alignment, 2 cm anterior knee translation (ANT), and 2 cm posterior knee translation (POST). In response to a destabilizing alignment perturbation (i.e., the ANT condition), participants significantly increased their early-stance hip extension moment, confirming that persons with transfemoral amputation rely on a hip extensor strategy to maintain knee joint stability. However, participants also decreased the rate at which they loaded their prosthesis, decreased their affected-side step length, increased their trunk flexion, and maintained their prosthesis in a more vertical posture at the time of opposite toe off. Collectively, these results suggest that persons with transfemoral amputation rely on a combination of strategies to coordinate stance-phase knee flexion. Further, comparatively few significant changes were observed in response to the POST condition, suggesting that a bias toward posterior alignment may have fewer implications in terms of stance-phase, knee joint control.

Comparing the effects of adapting to a weight on one leg during treadmill and overground walking: A pilot study

BACKGROUND

Locomotor adaptation has been suggested as a way to improve gait symmetry in individuals post-stroke. Most perturbation methods utilize costly, specialized equipment. The use of a unilateral leg weight may provide a low cost, clinically translatable alternative. Furthermore, previous studies have suggested that adaptation context may affect movement outcomes. The purpose of this study was to assess the ability of a unilaterally applied ankle weight to drive locomotor adaptation and determine the effect of context (treadmill versus overground) in young, non-disabled participants.

METHODS

Eighteen young non-disabled adults were randomly assigned to receive 10min of walking on a treadmill with a weight (TG), overground with a weight (OG) or as a control on a treadmill/overground without a weight (CG). Outcomes measured before, during and after adaptation were: step length symmetry, single limb support symmetry and gait speed.

RESULTS

After adding the weight, single limb support immediately became asymmetrical for all participants without changes in step length symmetry. After walking for 10min, TG step length became asymmetrical. After weight removal, both TG and OG had increased step length asymmetry. TG decreased single limb support asymmetry while OG did not. After walking overground without the weight, walking parameters eventually returned to baseline in both weighted groups. The control group showed no changes.

CONCLUSION

A unilaterally applied ankle weight appears able to cause gait adaptation in young, non-disabled participants. However different adaptive changes in the gait pattern are made by the nervous system when the perturbation is applied in different contexts.

The Effects of Visual Feedback Distortion with Unilateral Leg Loading on Gait Symmetry

Our prior work provides evidence that visual feedback distortion drives an implicit adaptation; a gradual distortion of visual representation of step length modulated subjects' step lengths away from symmetry. To further explore the effect of the visual feedback distortion on unconscious change in step symmetry, we investigated whether such adaptation would occur even in the presence of altered limb mechanics by adding mass to one side of the leg. 26 subjects performed three 8-min trials (weight only, weight plus visual feedback, and weight plus visual feedback distortion) of treadmill walking. During the weight only trial, the subjects wore a 5 lb mass around the right ankle. The modification of limb inertia caused asymmetric gait. The visual feedback showing right and left step length information as bar graphs was displayed on a computer screen. To add visual feedback distortion, we increased the length of one side of the visual bars by 10% above the actual step length, and the visual distortion was implemented for the side that took longer in response to the added mass. We found that even when adjustments were made to unilateral loading, the subjects spontaneously changed their step symmetry in response to the visual distortion, which resulted in a more symmetric gait. This change may be characterized by sensory prediction errors, and our results suggest that visual feedback distortion has a significant impact on gait symmetry regardless of other conditions affecting limb mechanics. A rehabilitation program employing visual feedback distortion may provide an effective way to restore gait symmetry.

The Effect of Backpack Load Carriage on the Kinetics and Kinematics of Ankle and Knee Joints During Uphill Walking

The purpose of this study was to investigate the effect of load carriage on the kinematics and kinetics of the ankle and knee joints during uphill walking, including joint work, range of motion (ROM), and stance time. Fourteen males walked at a self-selected speed on an uphill (15°) slope wearing military boots and carrying a rifle in hand without a backpack (control condition) and with a backpack. The results showed that the stance time significantly decreased with backpack carriage (p < .05). The mediolateral impulse significantly increased with backpack carriage (p < .05). In the ankle joints, the inversion-eversion, and dorsi-plantar flexion ROM in the ankle joints increased with backpack carriage (p < .05). The greater dorsi-plantar flexion ROM with backpack carriage suggested 1 strategy for obtaining high plantar flexor power during uphill walking. The result of the increased mediolateral impulse and inversion-eversion ROM in the ankle joints indicated an increase in body instability caused by an elevated center of mass with backpack carriage during uphill walking. The decreased stance time indicated that an increase in walking speed could be a compensatory mechanism for reducing the instability of the body during uphill walking while carrying a heavy backpack.

The effects of asymmetrical loading on gait characteristics

Asymmetrical load carriage is a popular method used among people in daily life. This study investigated the impact of asymmetrical load carriage and the load mass spatiotemporal parameters associated with gait patterns. Twelve participants were recorded as they walked under six load conditions. The loads included a control condition in which individuals carried no added load and loads of 10%, 15%, 20%, 25%, and 30% body weight carried with their right hand. Parameters used to describe the spatiotemporal characteristics of gait were quantified and analyzed. The results of the study demonstrated that the gait patterns of the individuals were affected by increases in the carried load. The loaded right side was more sensitive to changes in the loads carried. Overall, we conclude that the spatiotemporal parameters actually depend on the combination of both loading mass and the side that was loaded.

Asymmetrical Lower Extremity Loading Early After Anterior Cruciate Ligament Reconstruction Is a Significant Predictor of Asymmetrical Loading at the Time of Return to Sport

OBJECTIVES

The aim of this study was to examine whether asymmetrical lower limb loading early after anterior cruciate ligament reconstruction (1 mo) can predict asymmetrical lower limb loading at the time of return to sport (6 mos) and whether other early predictors as knee joint range of motion or maximal isometric strength affect this relationship.

DESIGN

Ground reaction forces were measured during a sit-to-stand task 1 mo after anterior cruciate ligament reconstruction and a vertical countermovement jump 6 mos after anterior cruciate ligament reconstruction in 58 athletes. Other early postoperative measurements were knee joint range of motion (2 wks, 1 mo, and 2 mos after surgery) and maximal isometric strength of the knee extensor and flexor muscles (2 mos after surgery). Linear regression models were developed using side-to-side limb symmetry index (LSI) of countermovement jump as the dependent variable.

RESULTS

LSI of sit-to-stand task 1 mo after surgery was a significant independent predictor of LSI of countermovement jump 6 mos after surgery. After accounting for deficits in knee joint range of motion and LSI of maximal isometric strength (ΔR² = 0.35, P < 0.01), LSI of sit-to-stand task predicted LSI of countermovement jump (ΔR² = 0.14 P < 0.01).

CONCLUSIONS

Asymmetrical lower extremity loading 1 mo after anterior cruciate ligament reconstruction is an early predictor of asymmetrical lower extremity loading 6 mos after surgery.

Functional Electrical Stimulation Alters the Postural Component of Locomotor Activity in Healthy Humans

Knowledge of the effects of Functional Electrical Stimulation (FES) of different intensity on postural stability during walking in healthy subjects is necessary before these relationships in patients with postural disorders can be assessed and understood. We examined healthy subjects in Control group walking on a treadmill for 40 min and in FES group-provided with 30 min of stimulation, which intensity increased every 10 min. The main difference between Control and FES group was the progressive increase of trunk oscillations in sagittal, frontal, and horizontal planes and an increase of relative stance duration in parallel with FES intensity increase. Both Control and FES groups exhibited shank elevation angle increase as an after-effect. It is concluded, that high intensity FES significantly changes the postural component of locomotor activity, but the fatigue signs afterwards were not FES specific.

Coping with asymmetry: how infants and adults walk with one elongated leg

The stability of a system affects how it will handle a perturbation: The system may compensate for the perturbation or not. This study examined how 14-month-old infants-notoriously unstable walkers-and adults cope with a perturbation to walking. We attached a platform to one of participants' shoes, forcing them to walk with one elongated leg. At first, the platform shoe caused both age groups to slow down and limp, and caused infants to misstep and fall. But after a few trials, infants altered their gait to compensate for the platform shoe whereas adults did not; infants recovered symmetrical gait whereas adults continued to limp. Apparently, adult walking was stable enough to cope with the perturbation, but infants risked falling if they did not compensate. Compensation depends on the interplay of multiple factors: The availability of a compensatory response, the cost of compensation, and the stability of the system being perturbed.

Gait disorder rehabilitation using vision and non-vision based sensors: a systematic review

Even though the amount of rehabilitation guidelines has never been greater, uncertainty continues to arise regarding the efficiency and effectiveness of the rehabilitation of gait disorders. This question has been hindered by the lack of information on accurate measurements of gait disorders. Thus, this article reviews the rehabilitation systems for gait disorder using vision and non-vision sensor technologies, as well as the combination of these. All papers published in the English language between 1990 and June, 2012 that had the phrases "gait disorder", "rehabilitation", "vision sensor", or "non vision sensor" in the title, abstract, or keywords were identified from the SpringerLink, ELSEVIER, PubMed, and IEEE databases. Some synonyms of these phrases and the logical words "and", "or", and "not" were also used in the article searching procedure. Out of the 91 published articles found, this review identified 84 articles that described the rehabilitation of gait disorders using different types of sensor technologies. This literature set presented strong evidence for the development of rehabilitation systems using a markerless vision-based sensor technology. We therefore believe that the information contained in this review paper will assist the progress of the development of rehabilitation systems for human gait disorders.

Harmonic ratios: a quantification of step to step symmetry

The harmonic ratio (HR), derived from the Fourier analysis of trunk accelerations, has been described in various ways as a measure of walking smoothness, walking rhythmicity, or dynamic stability. There is an increasing interest in applying the HR technique to investigate the impact of various pathologies on locomotion; however, explanation of the method has been limited. The aim here is to present a clear description of the mathematical basis of HRs and an understanding of their interpretation. We present harmonic theory, the interpretation of the HR using sinusoidal signals, and an example using actual trunk accelerations and harmonic analyses during limb-loading conditions. We suggest that the HR method may be better defined, not as a measure of rhythmicity or stability, but as a measure of step-to-step symmetry within a stride.

Transtibial amputee joint motion has increased attractor divergence during walking compared to non-amputee gait

The amputation and subsequent prosthetic rehabilitation of a lower leg affects gait. Dynamical systems theory would predict the use of a prosthetic device should alter the functional attractor dynamics to which the system self-organizes. Therefore, the purpose of this study was to compare the largest Lyapunov exponent (a nonlinear tool for assessing attractor dynamics) for amputee gait compared to healthy non-amputee individuals. Fourteen unilateral, transtibial amputees and fourteen healthy, non-amputee individuals ambulated on a treadmill at preferred, self-selected walking speed. Our results showed that the sound hip (p = 0.013), sound knee (p = 0.05), and prosthetic ankle (p = 0.023) have significantly greater largest Lyapunov exponents than healthy non-amputees. Furthermore, the prosthetic ankle has a significantly greater (p = 0.0.17) largest Lyapunov exponent than the sound leg ankle. These findings indicate attractor states for amputee gait with increased divergence. The increased attractor divergence seems to coincide with decreased ability for motor control between the natural rhythms of the individual and those of the prosthetic device. Future work should consider the impact of different prostheses and rehabilitation on the attractor dynamics.

Effects of prosthetic mass distribution on metabolic costs and walking symmetry

Unilateral, transtibial amputees exhibit walking asymmetries and higher metabolic costs of walking than nonamputees walking at similar speeds. Using lightweight prostheses has previously been suggested as a contributing factor to walking asymmetries. The purpose was to investigate the effects of prosthesis mass and mass distribution on metabolic costs and walking asymmetries among six unilateral, transtibial amputees. Kinematic and temporal symmetry did not improve when mass was added at different locations on the limb. Stance and swing time asymmetries increased by 3.4% and 7.2%, respectively, with loads positioned distally on the limb. Maximum knee angular velocity asymmetries increased by 6% with mass added to the thigh, whereas maximum thigh angular velocity asymmetries increased by approximately 10% with mass positioned near the prosthetic ankle. Adding 100% of the estimated mass difference between intact and prosthetic legs to the ankle of the prosthesis increased energy costs of walking by 12%; adding the same mass to the prosthesis center of mass or thigh center of mass increased metabolic cost by approximately 7% and 5%, respectively. Unless other benefits are gained by increasing prosthesis mass, this should not be considered as a possible alternative to current lightweight prosthesis designs currently being prescribed to unilateral amputees.

Walking speed, unilateral leg loading, and step symmetry in young adults

The purpose of this study was to examine the effects of gait speed and unilateral lower limb loading on step time and step length symmetry in healthy adults. Spatiotemporal gait data were collected from 22 healthy subjects (11 men, 11 women), using the GaitRite walkway, under four randomly sequenced test conditions: self-selected speed (SS), fast speed (F), self-selected speed with the right leg loaded (LSS), and the fastest attainable speed with the right leg loaded (LF). The symmetry index, calculated with the formula [((R-L)/0.5 × (R+L)) × 100], was used to quantify step time and step length symmetry. It was found that over-ground gait speed had no significant effects on the symmetry of step time or step length. Unilateral lower limb loading significantly increased step time asymmetry, with longer step time for the loaded leg. Step symmetry was further compromised and became more asymmetrical when, in addition to unilateral leg loading, subjects maximized their gait speed. This effect of fast speed with unilateral leg loading was particularly prominent in relation to step length, with its shortening in the unloaded leg and lengthening in the loaded leg. These observations in healthy subjects may serve as a reference for the assessment of gait symmetry in patients with unilateral lower limb pathologies.

The influence of visual perception of self-motion on locomotor adaptation to unilateral limb loading

Self-perception of motion through visual stimulation may be important for adapting to locomotor conditions. Unilateral limb loading is a locomotor condition that can improve stability and reduce abnormal limb movement. In the present study, the authors investigated the effect of self-perception of motion through virtual reality (VR) on adaptation to unilateral limb loading. Healthy young adults, assigned to either a VR or a non-VR group, walked on a treadmill in the following 3 locomotor task periods--no load, loaded, and load removed. Subjects in the VR group viewed a virtual corridor during treadmill walking. Exposure to VR reduced cadence and muscle activity. During the loaded period, the swing time of the unloaded limb showed a larger increase in the VR group. When the load was removed, the swing time of the previously loaded limb and the stance time of the previously unloaded limb showed larger decrease and the swing time of the previously unloaded limb showed a smaller increase in the VR group. Lack of visual cues may cause the adoption of cautious strategies (higher muscle activity, shorter and more frequent steps, changes in the swing and stance times) when faced with situations that require adaptations. VR technology, providing such perceptual cues, has an important role in enhancing locomotor adaptation.

Swing phase kinematic and kinetic response to weighting the hind pasterns

REASONS FOR PERFORMING STUDY

It is considered that specific exercises to strengthen limb musculature would be helpful.

OBJECTIVE

To describe swing phase kinematic and kinetic changes in the hindlimbs of trotting horses in response to the addition of leg weights to the hind pasterns.

METHODS

Six horses were prepared by placing reflective skin markers on the hindlimbs, the withers and fore hooves. Horses were evaluated at trot for 6 trials with and without leg weights (700 g) attached around the pasterns, with the 2 conditions applied in random order. The markers were tracked to determine peak heights of the flight arc of the hind hooves and swing phase joint angulations. Inverse dynamic analysis was used to calculate positive and negative work done across each joint in the first and second halves of the swing phase. Comparisons between conditions were made using paired t tests (normally distributed data) or the Wilcoxon rank-sum test (non-normally distributed data).

RESULTS

Peak height of the flight arc of the hind hooves was significantly higher with leg weights as a result of increased flexions of the stifle, tarsal and metatarsophalangeal joints. Increased positive (concentric) work was performed by the hip and tarsal musculature to protract and raise the limb in early swing, then to retract and lower the limb in late swing. Increased negative (eccentric) work was performed across the stifle and metatarsophalangeal joints to control their movements in response to increases in inertia and momentum due to the weights.

CONCLUSIONS

The addition of weight to the hind pasterns stimulates increased muscular activity across all the hindlimb joints from the hip to the metatarsophalangeal joint.

CLINICAL SIGNIFICANCE

The addition of weight to the hind pasterns may have therapeutic applications in activating and strengthening the hindlimb musculature. This is particularly relevant in the hip region, which appears more sensitive and responsive to the effect of weights than to tactile stimulation alone.