Richard R. Neptune

Individuals with unilateral transtibial amputation (TTA) often demonstrate asymmetrical gait patterns, which are further exacerbated during load carriage as passive prostheses cannot modulate their mechanical stiffness to accommodate the increased demand. Load carriage also increases the loads on the intact limb that can lead to overuse injuries and is also associated with increased metabolic cost and decreased forward propulsion. While active and passive load-suspended backpacks have been studied in healthy populations, no studies have explored the use of active backpacks to improve the walking performance for individuals with TTA. Therefore, the purpose of this study was to identify active backpack loading patterns to improve the metabolic cost, forward propulsion, and knee joint loading of individuals with TTA using a musculoskeletal simulation-based optimization framework. Different loading patterns were simulated using a time-varying actuator force applied to an active backpack over the gait cycle. The magnitude and timing of the actuator force were optimized for each performance criterion that resulted in a unique actuation pattern for each biomechanical measure. Interestingly, similar improvements relative to a passive backpack were observed across all actuation patterns, regardless of the optimization criteria. With all active backpacks, the force impulse experienced by the body from the dynamic load decreased, which resulted in increased forward propulsion, decreased intact knee joint loading, and improved metabolic cost. This suggests that active backpacks have the potential to improve walking performance during load carriage for individuals with TTA.

BACKGROUND Prosthetic foot selection may influence gait biomechanics in individuals with transtibial amputation, particularly during load carriage. While prior work often emphasizes intact limb compensation, this study examined prosthetic limb mechanics to directly assess device-user interaction. We compared five commercially available feet: a clinically prescribed foot, a stiffer category of the same foot, the same foot with a heel-stiffening wedge, a dual-keel foot, and a powered ankle-foot, across five load conditions: unloaded, anterior, posterior, intact side, and prosthetic side. METHODS Twelve participants performed overground walking trials at self-selected speed with each foot-load combination. Net positive and negative joint work at the prosthetic limb ankle, knee, and hip was calculated over the gait cycle and specific gait subphases via inverse dynamics. Linear mixed-effects models evaluated foot effects within load conditions. RESULTS Ankle joint work differed significantly between feet within all load conditions. The powered ankle-foot generated the highest net positive ankle work in late stance, suggesting enhanced propulsion. The clinically prescribed and heel-wedge feet produced the highest negative ankle work in early stance, indicating increased energy absorption. The stiffer and dual-keel feet reduced both positive and negative ankle work. Knee and hip joint work did not differ significantly across feet within load conditions. CONCLUSIONS Prosthetic foot type primarily modulates prosthetic ankle mechanics without altering proximal joint work under moderate load carriage. The powered ankle-foot may benefit users seeking propulsion, while non-powered designs may support energy absorption and stability. Prosthetic prescription should align with user mobility goals and expected load demands.

Individuals post-stroke with hemiparetic gait often experience impaired mobility, which can be restored using powered exoskeletons. Specifically, hip exoskeletons can deliver positive work to the leg to help initiate leg swing; however, it is unclear which limb assistance strategy (e.g., unilateral or bilateral assistance) best improves walking performance due to the asymmetric characteristics of hemiparetic gait. Therefore, the purpose of this study was to investigate how different hip exoskeleton limb assistance strategies affect lower-limb joint biomechanics during walking for individuals post-stroke. We hypothesized that bilateral assistance would best improve late stance paretic leg orientation and swing initiation, unilateral paretic limb assistance would improve interlimb asymmetries and unilateral nonparetic limb assistance would indirectly improve late stance kinematics. We found bilateral assistance significantly increased paretic hip flexion angle, providing an improvement in leg swing initiation, and improved ankle joint work symmetry, suggesting an improvement in propulsion mechanics. Unilateral paretic limb assistance significantly increased paretic knee flexion during swing, which is a common rehabilitative target to improve stiff-knee gait for individuals post-stroke, and significantly improved joint work symmetry between limbs, which is beneficial for individuals who have increased reliance on the nonparetic limb. Unilateral nonparetic assistance did not improve late stance kinematics. These results provide insight into joint-level responses of individuals post-stroke and can help tailor hip exoskeleton assistance for individuals post-stroke based on rehabilitation targets.

Prosthetic ankle-foot devices provide valuable assistance for individuals with a unilateral transtibial amputation (TTA) to effectively engage in daily living activities, although users often experience diminished walking performance such as increased metabolic cost, knee joint loading, and dynamic balance asymmetry due to the lack of torque control from commonly prescribed passive devices. Consequently, active powered prosthetic devices have been developed; however, it is unclear how to optimally tune them. The purpose of this study was to identify the optimal ankle torque profile of a powered ankle-foot prosthesis that improves walking performance for individuals with TTA. Specifically, we used a musculoskeletal simulation-based optimization framework to optimize a powered prosthesis torque profile while emulating group averaged kinematics and ground reaction forces (GRFs). We compared the metabolic cost, knee joint loading, sagittal plane dynamic balance symmetry, and torque profiles across the following simulated conditions: a passive prosthesis tracking individuals with TTA walking data, a powered prosthesis tracking able-bodied walking data, and a powered prosthesis that separately minimized metabolic cost, knee joint loading, and dynamic balance asymmetry. Distinct torque profiles emerged for each measure, but there was no clear trend in the positive prosthetic work performed, which suggests increased prosthetic work alone is insufficient to improve walking performance. Further analysis showed the prosthetic torque must be properly timed over the gait cycle to improve each measure. This study provides a framework for future work developing customized controllers for powered prostheses to improve various aspects of walking performance for individuals with TTA.

Biomechanical and metabolic differences between skipping and running suggest the nervous system may require an alternative motor control strategy to execute skipping. Motor control strategies can be compared across gaits by muscle modules based on which muscles are coactivated (module composition) and whether the same module compositions are used across gaits (module generalization). The purposes of this study were to identify and compare the module composition of skipping and running and determine the module generalization present across these two gaits. Six healthy young adults performed 10 s skipping and running trials on a treadmill at 2.5 m/s while electromyography (EMG) was collected from 8 muscles. A non-negative matrix factorization extracted motor modules from the EMG data. Generalization of modules, both at the group and individual level, was determined with correlations of module weights. Participants required 3.7 ± 0.5 (range: 3-4) modules to control skipping and 3.8 ± 0.4 (range: 3-4) modules to control running. Three generalized modules were found across gaits at the group level, and at the individual level each participant had at least one generalized module. The generalized modules contributed to similar biomechanical subtasks across gaits, highlighting similar gross motor task demands. The unique biomechanical demands of the skipping hop resulted in gait-specific control of the tibialis anterior and gluteus medius. Future work is needed to identify the factors that influence the amount of generalization an individual uses across locomotor tasks and whether the degree of generalization impacts the performance of each gait.

Individuals with lower-limb amputations are typically prescribed passive prosthetic feet for everyday walking. However, when carrying additional loads, users demonstrate increased reliance on their intact limb which can lead to overuse injuries. Powered prostheses have been shown to reduce compensations during unloaded walking, but their efficacy during load carriage remains unknown. Furthermore, how the position of an added load affects intact limb reliance is not well understood. This study determined (1) how the presence and placement of an added load affects between-limb joint work symmetry for individuals walking with transtibial protheses, and (2) how prosthetic foot type (passive or powered) affects joint work symmetry during load carriage. Kinematic and kinetic data were collected from unilateral transtibial prosthesis users (n = 12) wearing a passive or powered prosthesis while walking with no added load, a 13.6 kg load worn on the front of their torso, or the same load worn on their back. Work symmetry, calculated as the difference between intact-side and prosthesis-side net joint work, was determined for the ankle, knee and hip to quantify intact limb reliance. Ankle and hip work symmetry improved for the Front Load compared to the No Load condition, due to a tradeoff between intact ankle and intact hip demand. Furthermore, ankle work symmetry improved for all load conditions while wearing the powered prosthesis. These results highlight changes in compensatory strategies during different load carriage conditions and encourage the use of powered prostheses to reduce intact limb reliance during activities involving load carriage.

Individuals with transtibial amputation (TTA) are at increased risk for conditions such as intact-limb osteoarthritis and fatigue, likely due to elevated joint loading and metabolic cost compared to unimpaired individuals. These risks are amplified during load carriage, as individuals with TTA lack residual limb ankle plantarflexors and rely more heavily on their intact limb to meet increased mechanical demands. This study used musculoskeletal modeling and simulation to evaluate how different prosthetic feet and load carriage positions affect biomechanical demand during steady-state walking. Measures included total metabolic cost, individual muscle contributions to metabolic cost, and intact limb axial knee joint impulses. Walking data were collected from five individuals with TTA across five loading conditions (no-load and 30 lbs. carried as a front-, back-, intact-side-, or residual-side-load) while wearing four prosthetic feet (a passive standard-of-care foot, a stiffer foot, a heel-wedge-modified foot, and a dual-keel foot). Two participants also completed additional trials using a powered ankle-foot prosthesis. Front-load carriage resulted in the highest metabolic cost (7.56 ± 0.40 W * kg-1) while back-load carriage had the lowest (6.34 ± 0.38 W * kg-1). Key contributors to increased metabolic cost included the gastrocnemius, soleus, gluteus maximus and gluteus medius. Front-load carriage had the lowest intact knee joint impulse (16.56 ± 1.33 N * s * kg-1) while intact-side-load carriage had the highest (20.60 ± 1.39 N * s * kg-1). The optimal prosthetic foot varied greatly depending on load carriage position or biomechanical demand. These findings highlight the importance of tailoring both load carriage strategies and prosthetic foot prescriptions to the individual to optimize outcomes.

Maintaining appropriate lower-limb joint stiffness is critical for walking performance, as it facilitates tasks such as absorbing impact loading, maintaining balance, and providing body support and propulsion. Quasi-stiffness, an indirect measure describing the joint moment-angle relationship, is often used to assess joint stiffness during walking as it accounts for passive soft tissue stiffness and active muscle force generation. Thus, identifying the primary muscle contributors to joint moments and angles can elucidate how muscles are coordinated to maintain quasi-stiffness. However, determining individual muscle contributions experimentally is challenging. Therefore, the objective of this study was to use musculoskeletal modeling and simulation to identify individual muscle contributions to sagittal-plane quasi-stiffness during walking. Simulations of 15 healthy young adults were developed and individual muscle contributions to joint moments and angles were determined within discrete phases of the gait cycle. As expected, contributors to ankle, knee and hip moments were the primary dorsiflexors/plantarflexors, knee flexors/extensors, and hip flexors/extensors, respectively, as these muscles cross the joint and directly contribute to their respective joint moments. However, major contributors to the joint angles also included distant and contralateral muscles. Specifically, the hip extensors and ankle dorsiflexors were found to contribute to the knee angle (8.4-19.7% and 9.0-17.1% of total muscle contributions, respectively), while contralateral hip extensors were found to contribute (16.6-27.2%) to the hip angle. These results highlight the role of distant muscles in maintaining quasi-stiffness, and provide a foundation for developing rehabilitation strategies and assistive devices to target stiffness impairments in clinical populations.

Objective: To determine the item-level psychometrics of the Functional Gait Assessment (FGA) for persons with chronic stroke and create a keyform (or score sheet) for clinicians. Design: Retrospective cohort. Setting: Archival item-level data from a research database. Participants: One-hundred-one ambulatory persons (N=101) with chronic stroke (44% women, 58% right hemiparesis, average age 59y, lower extremity Fugl-Meyer 25, and overground self-selected walking speed 0.76 m/s). Interventions: Not applicable. Main Outcome Measures: A principal component analysis of the residuals from the Andrich Rating Scale Model (RSM) was used to evaluate unidimensionality and item local dependence. The RSM was also used to examine the rating scale structure, item and person fit, item difficulty hierarchy, and person separation index and to generate a keyform. Results: Principal component analysis of the residuals confirmed the FGA's unidimensionality and that no items had local dependence. The category rating scale met the criterion and advanced monotonically. The item difficulty hierarchy was similar to that of community-dwelling older adults. The sample's mean ability level (ie, person measure) was 0.28 logits (SE=0.63). The FGA had high person reliability (0.90) despite 10% of persons misfitting. There were no floor or ceiling effects, and the FGA separated people into 4 strata. The scored FGA keyform visually showed an individual's response pattern relative to their measure value. Conclusion: Rasch analysis supports the use of the FGA to measure walking balance ability in ambulatory persons with chronic stroke. An FGA keyform can provide instantaneous interval measurement for individuals.

BACKGROUND Load carriage can exacerbate the elevated intact limb knee loading in individuals with transtibial amputation, potentially contributing to osteoarthritis. Prosthetic foot mechanical properties like push-off power have the potential to reduce this elevated knee loading. This study investigated how load carriage position and prosthetic foot type affect intact limb knee loading measures for these individuals. METHODS Twelve participants with unilateral transtibial amputation were recruited. Intact limb external knee adduction and flexion moments were analyzed, with prosthetic push-off power and work quantified for effects on first peak knee adduction moment. A linear mixed-effects regression evaluated the effects of load position and prosthetic foot on these metrics. FINDINGS Participants exhibited the smallest first peak knee adduction moment and impulse with the intact-side load condition, followed by the back load and front load conditions, with the prosthetic-side load condition having the highest magnitude (20-35 % increase). However, we found no significant differences in these metrics by prosthetic foot. Additionally, load position and prosthetic foot did not significantly affect peak knee flexion moment. Only a negative trend toward correlation (P = 0.089) was observed between first peak knee adduction moment and prosthetic push-off work in the back load condition. INTERPRETATION Intact-side load carriage may be more clinically beneficial for mitigating the risk of increased intact limb knee loading. Further, load carriage strategy affects intact limb knee loading more than specific prosthetic foot type. These biomechanical findings can help guide rehabilitative load carriage strategies to minimize the elevated risk of knee osteoarthritis in individuals with transtibial amputation.

Stiff-Knee gait (SKG) commonly occurs in individuals after stroke, loosely defined as reduced peak knee flexion angle during swing. The causes of SKG are multifaceted and debated. Further, clinical interventions have not been consistently effective, possibly resulting from multiple undiagnosed subtypes of SKG. Thus, our primary goal of this study is to explore the existence of potential subtypes associated with different levels of motor control complexity. We used retrospective kinematics, kinetics and muscle activity from 50 stroke survivors and 15 healthy, age-matched controls during treadmill walking. We used a time-series kernel k-means cluster analysis based on compensatory frontal plane kinematics associated with SKG to separate participants into three groups, Cluster A (hip hiking, lowest knee flexion, highest propulsion asymmetry, lowest gait speed), Cluster B (hip hiking and hip abduction, moderate knee flexion, middle gait speed) and Cluster C (highest knee flexion, highest gait speed). The highest proportion of individuals with SKG as diagnosed by a clinician were in Cluster A, but with a substantial proportion in Cluster B, indicating that these two clusters can be considered subtypes of SKG. Despite differences in kinematics and kinetics, we did not observe fundamental differences in underlying motor control between clusters as determined by non-negative matrix factorization of measured muscle activations. We conclude that the differences between clusters were most likely attributed to the severity of gait impairment, as reflected by slower gait speed and propulsion asymmetry, rather than being a different type of SKG.

Skipping represents a training alternative to running due to its lower knee contact forces and higher whole-body metabolic cost. The increased metabolic cost of skipping is associated with a higher vertical center-of-mass (COM) displacement during the support and flight phases of the skipping hop compared to running. However, skipping has lower muscle force impulses than running. Therefore, the study purpose was to compare the flow of mechanical power between body segments during skipping and running to determine the mechanisms enabling higher vertical displacement in skipping despite the lower vertical impulse. Running and skipping cycles were simulated in OpenSim for 5 adults (22.4 ± 2.2 y) using motion capture data collected at 2.5 m/s on an instrumented dual-belt treadmill. A segmental power analysis quantified muscle contributions to vertical body segment mechanical power, which were integrated over the stance phase of running (Run) and the hop (Skip 1) and step (Skip 2) of skipping to calculate mechanical work. Higher vertical work was done by the gluteus maximus, vasti, and soleus in Skip 1, primarily through power generation to the trunk, compared to power absorption in Run and Skip 2. Thus, despite lower muscle force impulses in Skip 1, muscles generate power through concentric contractions, leading to greater metabolic cost than in running. These muscle force impulses contribute to propelling the COM upward in Skip 1 (rather than decelerating downward COM motion in Run and Skip 2), which raises the COM and contributes to the greater COM displacement in skipping compared to running.

BACKGROUND Ambulatory individuals with lower limb amputations often face challenges with body support, body propulsion, and balance control. Carrying an infant, toddler, backpack, or other load can exacerbate these challenges and highlights the importance of prescribing the most suitable prosthetic foot. The aim of this study was to examine the influence of five different prosthetic feet on walking performance during various load carriage conditions. METHODS Biomechanical data were collected from twelve participants wearing five different prosthetic feet (four passive, one powered) while walking with no added load and carrying a load of 13.6 kg in four different positions: posterior, anterior, prosthetic side, and intact side. FINDINGS Based on our study population, a powered-ankle-foot offers additional body support when a load is carried posteriorly. If additional forward propulsion is needed while carrying a load anteriorly, a heel wedge is better than a stiffer foot. For individuals who may need additional sagittal plane balance control, no study foot was advantageous regardless of how the load was carried. For those who need additional frontal plane balance control during posterior load carriage, a heel wedge is better than a stiffer or powered foot. Lastly, the standard-of-care, heel wedge, and dual keel feet provided more frontal plane balance control than a powered foot when a load was carried anteriorly. INTERPRETATION For individuals with lower limb amputation who carry loads, consideration of their preferred load carrying method may help select an appropriate prosthetic foot for body support, propulsion, and balance control.

Carrying side loads often occurs during activities of daily living. As walking is most unstable mediolaterally, side load carriage may further compromise gait biomechanics, especially for transtibial amputees (TTAs). This study investigated the effects of side load carriage on gait kinetics during steady-state walking to determine which side, intact or prosthetic, TTAs should carry a load. Twelve unilateral TTAs wore a passive-elastic foot and carried a side load of 13.6 kg while walking at their self-selected speed. Kinetic metrics, including ground reaction force peaks and impulses, loading and unloading rates, and joint moments and powers, were analyzed. TTAs had smaller propulsive forces on their intact limb during the prosthetic side load condition. During the intact side load condition, they had smaller hip flexor moment in late stance and smaller knee flexor moment at the end of swing on their intact limb. They had higher hip and knee abductor moments on their intact limb and prosthetic limb in early and late stance during the contralateral side load condition. TTAs generated higher hip extensor power at weight acceptance during the ipsilateral side load. Significant interactions were observed in hip extensor power and abductor moment, suggesting strong associations between hip extensor power generation and the ipsilateral side load and between hip abductor moment and the contralateral side load. These mixed results demonstrate some kinetic changes due to side load carriage and suggest that the side TTAs should carry a load depends on the desired effects, primarily on their intact limb.

Individuals with transtibial amputation (TTA) experience altered gait mechanics, which are primarily attributed to the functional loss of the ankle plantarflexors. The plantarflexors contribute to body support and propulsion and play an important role in adapting to different load carriage conditions. However, how muscle function is altered across different prosthetic foot types and load carriage scenarios for individuals with TTA remains unclear. This study used musculoskeletal modeling and simulation of human movement in OpenSim to investigate the effects of a range of prosthetic feet and load conditions on individual muscle and prosthetic foot contributions to body support and propulsion. Twenty walking trials were collected from five individuals with TTA, consisting of five loading conditions (no-load; 30 lbs (13.6 kg) carried as a front-load, back-load, intact-side-load and residual-side-load) while wearing four prosthetic feet (their passive standard of care (SOC) foot, their SOC foot one category stiffer, their SOC foot with a heel stiffening wedge, and a dual-keel foot). Two participants also wore a powered ankle-foot prosthesis, thus completing an additional five trials each. The results indicated that the front-load condition may be more challenging because it required overall increased muscle contributions to body support and propulsion. However, the front- and residual-side-loads required reduced intact-side plantarflexor contributions to support and propulsion, and thus may be advantageous for individuals with plantarflexor weakness. Further, the large variability across contributions suggests that individuals with TTA may rely on a variety of compensatory mechanisms depending on the load condition and prosthetic foot used.

The back handspring step out (BHS) is a foundational skill in gymnastics balance beam routines that requires the generation of significant sagittal plane angular momentum while tightly regulating frontal plane momentum to control their balance. However, which body segments are critical for generating this momentum and successfully performing the BHS and whether skill level influences this generation remains unknown. Twenty-five gymnasts with a range of skill levels performed a BHS on a balance beam. The BHS was scored, and segmental contributions to whole-body angular momentum were analyzed during the take-off, flight, hand contact and landing phases. Angular momentum has previously been used to assess balance control, where higher ranges of frontal plane angular momentum are indicative of poorer balance control. There were no differences in segmental contributions to angular momentum during the take-off phase between high- and low-scoring groups. However, the low-scoring group had higher trunk contributions to frontal plane angular momentum after the take-off phase. The trailing leg was also found to be a large contributor to frontal plane angular momentum, and thus more likely than the leading leg to cause deviations in balance control. In the sagittal plane, momentum generation and skill level were weakly correlated, suggesting as gymnasts become more skilled, they produce larger sagittal plane motions and are more adept at generating angular momentum. Because the trunk and trailing leg had high contributions to frontal plane angular momentum, controlling the trunk and trailing leg should be a focus in training regimes to improve BHS performance.

BACKGROUND: Stiff-Knee gait affects 25-75 % of individuals with post-stroke gait impairment and is typically defined as reduced swing phase knee flexion. Different studies use various measures to identify Stiff-Knee gait, such as peak swing knee flexion angle, timing of peak knee flexion, knee range of motion, and ankle push-off acceleration, leading to inconsistent results. METHODS: This study used univariate cluster analysis to examine the independence, consistency, validity, and accuracy of different definitions in 50 post-stroke individuals (24 with and 26 without Stiff-Knee gait), as determined by a physiatrist. Spearman's rank correlation was used for correlation analysis, and five clustering techniques along with clinician evaluations were used for validity analysis. FINDINGS: Correlation analysis showed that peak knee flexion timing and knee hyperextension are poorly correlated with reduced swing-phase knee flexion angle (ρ = -0.09 and ρ = -0.26 respectively). Validity analysis indicated that the between-limb difference in peak swing knee flexion angle and peak swing knee flexion angle at self-selected gait speeds were the most valid differentiators. At the fastest comfortable gait speed, the between-limb difference of peak knee flexion angle had the highest sensitivity, lowest specificity, and highest F1 scores. INTERPRETATION: We determined thresholds of less than 44.3° for peak swing knee flexion angle and greater than 17.0° for the between-limb difference of peak knee flexion angle identify Stiff-Knee gait during self-selected walking. We recommend using the difference in peak swing knee flexion angle between limbs to diagnose post-stroke Stiff-Knee gait due to its robustness to changes in gait speed.

Skipping is a common speed training exercise and a transitional rehabilitation activity between walking and running. Skipping has a greater metabolic cost than running, which is associated with greater vertical displacement of the body’s center of mass (COM). Muscle forces perform mechanical work to raise the COM, yet our recent work revealed lower muscle force impulses in skipping compared to running, particularly in the ankle plantarflexors. PURPOSE: To determine the mechanisms enabling greater vertical displacement in skipping despite lower muscle force impulses. METHODS: Running and skipping cycles were simulated in OpenSim for 5 adults (22.4 ± 2.2 y) using motion capture and ground reaction force (GRF) data collected at 2.5 m/s on an instrumented dual-belt treadmill. A segmental power analysis quantified muscle contributions to vertical mechanical power, which were integrated over the stance phase of running (Run) and the hop step of skipping (Skip). Paired t-tests compared vertical COM kinematics, vertical GRF impulses, and muscle contributions to vertical work between gaits. RESULTS: Skip had lower negative landing and greater positive take-off COM velocities than Run (Fig 1A, p < 0.05) and greater COM displacement during the stance and flight phases (Fig 1B, p < 0.05). GRF impulses were not different between gaits (Fig 1C). In Skip, the plantarflexors, quadriceps, and gluteal muscles generated greater positive vertical work while the hamstrings and tibialis anterior generated greater negative work than in Run (Fig 1D, p < 0.05). CONCLUSION: Due to lower negative vertical landing velocity in Skip, less work was required to redirect the COM, which began to move upward earlier in stance. Thus, the plantarflexors (despite producing lower force impulses), quadriceps and gluteal muscles generated greater net positive vertical work in Skip, which produced greater changes in vertical COM position during stance, take-off velocity, and COM position during flight.

Although the back handspring step out (BHS) is a foundational skill in balance beam routines, it can be performed using different take-off techniques. Back injuries are highly prevalent in the BHS due to the combination of high spine extension and joint loading. However, it is unclear which technique minimises injury risk or leads to better BHS performance. The purpose of the study was to identify techniques used for the BHS take-off and analyse the resulting BHS performance. Gymnasts were found to use either: Simultaneous Flexion-trunk and knees flex at the same time; Sequential Flexion-trunk reaches its maximum flexion followed by knee flexion; or Double-Bounce-knees and trunk both flex and then the knees extend and flex again. To assess performance, point deductions were calculated, and dynamic balance, ground reaction forces (GRFs) and relevant joint angles were analysed. The techniques had no differences in point deductions or dynamic balance, but there were differences in GRFs, spine extension and knee flexion. The Sequential Flexion technique had the lowest spine extension, which potentially reduces back injuries and the lowest knee flexion, which is a BHS requirement. These results support the use of Sequential Flexion technique when performing the BHS.

Well-prescribed prosthetic feet are critical to restore gait for persons with limb loss. Criteria for prescription can be difficult to define due to differences in individuals and few measurements defining the mechanical properties of prostheses. The use of a robotic ankle in series with a prosthesis can provide biological levels of mechanical power during gait. In addition, active ankle prostheses can adapt to different use cases. To assess how this paradigm influences user assistance, we quantified the effective stiffness of standalone feet of varying clinical stiffness categories in comparison to a robotic ankle in series with a fixed category level prosthetic foot. We hypothesized that control of a powered ankle across its range of stiffness and damping parameters can expand the effective stiffness range offered by commercially available passive feet, and better explain the effective stiffness rendered during loading. Benchtop compression loading was completed on energy storage and return feet of manufacturer-defined stiffness category levels (4–9), as well as an integrated prosthetic foot (category 9) and robotic ankle system. Force-displacement data were used to characterize stiffness in toe- and heel-only loading, at low (--0-50% body weight) and high (--50-100<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">%</sup>) end levels. Control of the ankle captured well most of the profiles of standalone feet, as well as responses outside of these behaviors at low stiffness. Generally, there were stronger linear relationships between effective stiffness and category level of standalone feet (r=~0.9), and less so between the stiffness gain of the robotic ankle and effective stiffness (r=~0.8). The exception was for high-end toe-only loading of the standalone and robotic conditions (r=0.76 and 0.92, respectively).

When performing the back handspring step out (BHS) on the balance beam, most gymnasts use one of three take-off techniques: Simultaneous Flexion, Sequential Flexion or Double-Bounce. However, it remains unclear which technique results in the lowest muscle demand that could help reduce energy expenditure and fatigue and improve overall performance. The purpose of this study was to use musculoskeletal modelling and simulation to quantify the influence of take-off technique on muscle demand (integrated muscle power) and contributions to the critical biomechanical functions of whole-body angular momentum generation and control and trunk propulsion (mechanical power delivered to the trunk). Simulations of female gymnasts (n = 21; age: 15.3 ± 3.6) were generated using their self-selected BHS technique on a balance beam. Differences in muscle demand were small across the techniques. However, the vasti, ankle plantarflexors, gluteus maximus and hamstring muscle groups experienced large demand during the BHS take-off. The gluteus medius and ankle plantarflexors were crucial for maintaining balance. The hamstrings, ankle plantarflexors and vasti generated needed momentum and delivered power to the trunk. These results provide targets for muscle strengthening and conditioning to improve balance control and increase the height and distance of the BHS, which is needed before adding additional skills in combination.

BACKGROUND Community ambulation involves complex walking adaptability tasks such as stepping over obstacles or taking long steps, which require adequate propulsion generation by the trailing leg. Individuals post-stroke often have an increased reliance on their trailing nonparetic leg and favor leading with their paretic leg, which can limit mobility. Ankle-foot-orthoses are prescribed to address common deficits post-stroke such as foot drop and ankle instability. However, it is not clear if walking with an ankle-foot-orthosis improves inter-limb propulsion symmetry during adaptability tasks. This study sought to examine this hypothesis. METHODS Individuals post-stroke (n = 9) that were previously prescribed a custom fabricated plantarflexion-stop articulated ankle-foot-orthosis participated. Participants performed steady-state walking and adaptability tasks overground with and without their orthosis. The adaptability tasks included obstacle crossing and long-step tasks, leading with both their paretic and nonparetic leg. Inter-limb propulsion symmetry was calculated using trailing limb ground-reaction-forces. FINDINGS During the obstacle crossing task, ankle-foot-orthosis use resulted in a significant improvement in inter-limb propulsion symmetry. The orthosis also improved ankle dorsiflexion during stance, reduced knee hyperextension, increased gastrocnemius muscle activity, and increased peak paretic leg ankle plantarflexor moment. In contrast, there were no differences in propulsion symmetry during steady-state walking and taking a long-step when using the orthosis. INTERPRETATION Plantarflexion-stop articulated ankle-foot-orthoses can improve propulsion symmetry during obstacle crossing tasks in individuals post-stroke, promoting paretic leg use and reduced reliance on the nonparetic leg.

Individuals with transtibial amputation (TTA) experience asymmetric lower-limb loading which can lead to joint pain and injuries. However, it is unclear how walking over unexpected uneven terrain affects their loading patterns. This study sought to use modeling and simulation to determine how peak joint contact forces and impulses change for individuals with unilateral TTA during an uneven step and subsequent recovery step and how those patterns compare to able-bodied individuals. We expected residual limb loading during the uneven step and intact limb loading during the recovery step would increase relative to flush walking. Further, individuals with TTA would experience larger loading increases compared to able-bodied individuals. Simulations of individuals with TTA showed during the uneven step, changes in joint loading occurred at all joints except the prosthetic ankle relative to flush walking. During the recovery step, intact limb joint loading increased in early stance relative to flush walking. Simulations of able-bodied individuals showed large increases in ankle joint loading for both surface conditions. Overall, increases in early stance knee joint loading were larger for those with TTA compared to able-bodied individuals during both steps. These results suggest that individuals with TTA experience altered joint loading patterns when stepping on uneven terrain. Future work should investigate whether an adapting ankle-foot prosthesis can mitigate these changes to reduce injury risk.

The majority of manual wheelchair users (MWCU) develop shoulder pain or injuries, which is often caused by impingement. Because propulsion mechanics are influenced by the recovery hand pattern used, the pattern may affect shoulder loading and susceptibility to injury. Shoulder muscle weakness is also correlated with shoulder pain, but how shoulder loading changes with specific muscle group weakness is unknown. Musculoskeletal modeling and simulation were used to compare glenohumeral joint contact forces (GJCFs) across hand patterns and determine how GJCFs vary when primary shoulder muscle groups are weakened. Experimental data were analyzed to classify individuals into four hand pattern groups. A representative musculoskeletal model was then developed for each group and simulations generated to portray baseline strength and six muscle weakness conditions. Three-dimensional GJCF peaks and impulses were compared across hand patterns and muscle weakness conditions. The semicircular pattern consistently had lower shear (anterior-posterior and superior-inferior) GJCFs compared to other patterns. The double-loop pattern had the highest superior GJCFs, while the single-loop pattern had the highest anterior and posterior GJCFs. These results suggest that using the semicircular pattern may be less susceptible to shoulder injuries such as subacromial impingement. Weakening the internal rotators and external rotators resulted in the greatest increases in shear GJCFs and decreases in compressive GJCF, likely due to decreased force from rotator cuff muscles. These findings suggest that strengthening specific muscle groups, especially the rotator cuff, is critical for decreasing the risk of shoulder overuse injuries.

BACKGROUND Balance perturbation studies during walking have improved our understanding of balance control in various destabilizing conditions. However, it is unknown to what extent balance recovery strategies can be generalized across different types of mediolateral balance perturbations. RESEARCH QUESTION Do similar mediolateral perturbations (foot placement versus surface translation) have similar effects on balance control and corresponding balance response strategies? METHODS Kinetic and kinematic data were previously collected during two separate studies, each with 15 young, healthy participants walking on an instrumented treadmill. In both studies, medial and lateral balance perturbations were applied at 80% of the gait cycle either by a treadmill surface translation or a pneumatic force applied to the swing foot. Differences in balance control (frontal plane whole body angular momentum) and balance response strategies (hip abduction moment, ankle inversion moment, center of pressure excursion and frontal plane trunk moment) between perturbed and unperturbed gait cycles were evaluated using statistical parametric mapping. RESULTS Balance disruptions after foot placement perturbations were larger and sustained longer compared to surface translations. Changes in joint moment responses were also larger for the foot placement perturbations compared to the surface translation perturbations. Lateral hip, ankle, and trunk strategies were used to maintain balance after medial foot placement perturbations, while a trunk strategy was primarily used after surface translations. SIGNIFICANCE Surface and foot placement perturbations influence balance control and corresponding response strategies differently. These results can help inform the development of perturbation-based balance training interventions aimed at reducing fall risk in clinical populations.

Quasi-stiffness describes the intersegmental joint moment-angle relationship throughout the progression of a task. Previous work has explored sagittal-plane ankle quasi-stiffness and its application for the development of powered lower-limb assistive devices. However, frontal-plane quasi-stiffness remains largely unexplored but has important implications for the development of exoskeletons since clinical populations often walk with wider steps and rely on frontal-plane balance recovery strategies at the hip and ankle. This study aimed to characterize frontal-plane hip and ankle quasi-stiffness during walking and determine how step width affects quasi-stiffness in both the frontal and sagittal planes. Kinematic and kinetic data were collected and quasi-stiffness values computed for healthy young adults (n = 15) during treadmill walking across a range of step widths. We identified specific subphases of the gait cycle that exhibit linear and quadratic frontal-plane quasi-stiffness approximations for the hip and ankle, respectively. In addition, we found that at wider step widths, sagittal-plane ankle quasi-stiffness increased during early stance (∼12-35% gait cycle), sagittal-plane hip quasi-stiffness decreased in late stance (∼40-55% gait cycle) and frontal-plane hip quasi-stiffness decreased during terminal stance (∼48-65% gait cycle). These results provide a framework for further exploration of frontal-plane quasi-stiffness, lend insight into how quasi-stiffness may relate to balance control at various step widths, and motivate the development of stiffness-modulating assistive devices to improve balance related outcomes.

&lt;p&gt;Walking on uneven terrain is a common task throughout daily living and can cause changes in lower-limb kinematics and mechanics. Joint loading, while difficult to measure experimentally, may also increase on uneven terrain, which could contribute to the development of joint pain and debilitating conditions. This study investigated how lower-limb joint loading is affected during a step on coronally-uneven terrain and during the subsequent recovery step using data from individuals without mobility impairments (n=5) and musculoskeletal modeling and simulation, which can be used to reliably estimate joint contact forces. The simulations indicated changes in joint loading during both the uneven and recovery steps on uneven terrain compared to level-ground walking, and these changes varied throughout stance. During both the uneven and recovery steps, the largest increases in peak joint contact forces and impulses were at the ankle joint during early stance. These results suggest that individuals may rely more on early compensations at the ankle than compensations at the hip or knee throughout stance. Future work should include populations with mobility impairments and investigate if different compensatory strategies or interventions can influence the outcomes.&lt;/p&gt;

Walking on uneven terrain is a common task throughout daily living and can cause changes in lower-limb kinematics and mechanics. Joint loading, while difficult to measure experimentally, may also increase on uneven terrain, which could contribute to the development of joint pain and debilitating conditions. This study investigated how lower-limb joint loading is affected during a step on coronally-uneven terrain and during the subsequent recovery step using data from individuals without mobility impairments (n=5) and musculoskeletal modeling and simulation, which can be used to reliably estimate joint contact forces. The simulations indicated changes in joint loading during both the uneven and recovery steps on uneven terrain compared to level-ground walking, and these changes varied throughout stance. During both the uneven and recovery steps, the largest increases in peak joint contact forces and impulses were at the ankle joint during early stance. These results suggest that individuals may rely more on early compensations at the ankle than compensations at the hip or knee throughout stance. Future work should include populations with mobility impairments and investigate if different compensatory strategies or interventions can influence the outcomes.

Physical fatigue accounts for many injuries in the workplace, sports arena, or battlefield. The traditional approaches to monitor fatigue rely on detecting and measuring shifts in the person’s muscular surface electromyography (sEMG) signals. However, assessing neuromuscular fatigue based purely on sEMG signals fails to account for the changing muscle dynamics during long dynamic physical tasks. To combat this dilemma, a system-based methodology has been recently developed and applied to several upper-extremity tasks. In this paper, we validate the efficacy of this novel methodology on the lower extremities during a dynamic activity. Specifically, the system-based monitoring methodology was applied to a cycling endurance task. It was statistically demonstrated that the system-based methodology resulted in a more-sensitive and less noisy metric, in comparison with an EMG-based methodology. The efficacy of the methodology was further illustrated by analyzing the inter-segmental recovering and fatiguing trends, which aligned with each muscle’s expected inter-muscle synergistic relationship.

Gait asymmetry is a predictor of fall risk and may contribute to increased falls during pregnancy. Previous work indicates that pregnant women experience asymmetric joint laxity and pelvic tilt during standing and asymmetric joint moments and angles during walking. How these changes translate to other measures of gait asymmetry remains unclear. Thus, the purpose of this case study was to determine the relationships between pregnancy progression, subsequent pregnancies, and gait asymmetry. Walking data were collected from an individual during 2 consecutive pregnancies during the second and third trimesters and 6 months postpartum of her first pregnancy and the first, second, and third trimesters and 6 months postpartum of her second pregnancy. Existing asymmetries in step length, anterior-posterior (AP) impulses, AP peak ground reaction forces, lateral impulses, and joint work systematically increased as her pregnancy progressed. These changes in asymmetry may be attributed to pelvic asymmetry, leading to asymmetric hip flexor and extensor length, or due to asymmetric plantar flexor strength, as suggested by her ankle work asymmetry. Relative to her first pregnancy, she had greater asymmetry in step length, step width, braking AP impulse, propulsive AP impulse, and peak braking AP ground reaction force during her second pregnancy, which may have resulted from increased joint laxity.

Individuals with neuromuscular deficits often walk with wider step widths compared to healthy adults. Wider steps have been linked to a higher destabilizing frontal-plane external moment and greater range of frontal-plane whole-body angular momentum (HR), which is an indicator of decreased balance control. The purpose of this study was to experimentally determine 1) how step width alters balance control during steady-state walking, and 2) if step width changes the balance response strategies following mediolateral surface perturbations in healthy adults. Fifteen healthy young adults (7 male, age: 25 ± 4 years) walked on an instrumented treadmill at narrow, self-selected, wide and extra-wide step widths. During perturbed trials, the treadmill provided random mediolateral surface translations to each foot midway through single-leg-stance. Muscle electromyography, biomechanical measures (HR, frontal-plane external moment and joint moments) and deviations (differences in these measures between the perturbed and unperturbed walking trials) were compared across step widths. During steady state walking, wider steps were associated with decreased balance control. Increasing step widths were also associated with increased gluteus medius activity and reduced hip abduction and ankle inversion moments, which suggests healthy subjects rely more on a lateral ankle strategy to maintain balance at increasing step widths. There was no change in the plantarflexion moment. During perturbed walking, lateral, but not medial, surface translations adversely affected balance control. Further, wider steps did not change the balance response strategies following the perturbations, which suggests healthy individuals have the capacity to respond similarly to the perturbations at different step widths.

Coronally uneven surfaces are prevalent in natural and man-made terrain, such as holes or bumps in the ground, curbs, sidewalks, and driveways. These surfaces can be challenging to navigate, especially for individuals with lower limb amputations. This study examined the biomechanical response of individuals with unilateral transtibial amputation (TTA) taking a step on a coronally uneven surface while wearing their clinically prescribed prosthesis, compared to individuals without mobility impairments (controls). An instrumented walkway was used with the middle force plate positioned either flush or rotated ± 15˚ in the coronal plane and concealed (blinded). TTAs used greater hip abduction compared to controls across all conditions, but especially during blinded inversion. The recovery step width of TTAs was wider after blinded eversion and narrower after blinded inversion, but unchanged for controls. These results suggest TTAs may have decreased balance control on unexpected, uneven surfaces. Additionally, TTAs generated less positive prosthetic ankle joint work during blinded inversion and eversion, and less negative coronal hip joint work during blinded inversion compared to controls. These biomechanical responses could lead to increased energy expenditure on uneven terrain. Surface condition had no effect on the vertical center of mass for either group of participants. Finally, the TTAs and the control group generated similar vertical GRF impulses, suggesting the TTAs had sufficient body support despite differences in surface conditions. These results are important to consider for future prosthetic foot designs and rehabilitation strategies.

Abstract Balance perturbations are often used to gain insight into reactive control strategies used to prevent falls. We developed a perturbation platform system (PPS) that can induce perturbations in both vertical and angled directions. The PPS was evaluated using human subject testing to verify its function and performance. The final system consisted of two box platforms that can individually perform vertical and angled surface perturbations. Following a perturbation, the system can automatically reset for the next iteration under the weight of the standing participant. The PPS achieves a peak downward acceleration of 4.4 m/s2 during drop events that simulate sudden surface changes. The experimental testing revealed that the perturbation induced a peak limb loading of 280 ± 38% of body weight (BW) during vertical drops and that participants' center of mass displacements were consistent with previous balance studies evaluating vertical perturbations. The system can be used in a laboratory or clinical setting to better understand balance response and control mechanisms and assist in rehabilitation training to improve balance control and help mitigate the incidence of falls.<br><br>ASME © Originally published in Journal of Medical Devices. <br><br>Deposited by shareyourpaper.org and openaccessbutton.org. We've taken reasonable steps to ensure this content doesn't violate copyright. However, if you think it does you can request a takedown by emailing help@openaccessbutton.org.

BACKGROUND Clinical populations often walk with altered foot placement, which can adversely affect balance control. However, it is unknown how balance control during walking is influenced when combining a cognitive load with altered foot placement. RESEARCH QUESTION Is balance control during walking adversely affected by the combination of a more complex motor task, such as walking with altered foot placements, with a cognitive load? METHODS Fifteen young healthy adults walked on a treadmill with and without a spelling cognitive load during normal walking, with step width targets (self-selected width, narrow, wide and extra wide), or with step length targets (self-selected length, short and long). RESULTS Cognitive performance, measured by correct spelling response rate, decreased from self-selected (2.407 ± 0.6 letters/s) to the extra wide width (2.011 ± 0.5 letters/s). The addition of the cognitive load caused a decrease in frontal plane balance control across all step lengths (15% change) and at the wider step widths (16% change), but only caused a slight decrease in the sagittal plane for the short step length (6.8% change). SIGNIFICANCE These results suggest that when combining a cognitive load with walking at non-self-selected widths, a threshold exists at wider steps where attentional resources become insufficient and balance control and cognitive performance decrease. Because decreased balance control increases the risk of falling, these results have implications for clinical populations who often walk with wider steps. Furthermore, the lack of changes to sagittal plane balance during altered step length dual-tasks further supports that frontal plane balance requires more active control.

Knowledge regarding the neural origins of distinct upper extremity impairments may guide the choice of interventions to target neural structures responsible for specific impairments. This cross-sectional pilot study investigated whether different brain networks explain distinct aspects of hand grip performance in stroke survivors. In 22 chronic stroke survivors, hand grip performance was characterized as grip strength, reaction, relaxation times, and control of grip force magnitude and direction. In addition, their brain structural connectomes were constructed from diffusion tensor MRI. Prominent networks were identified based on a two-step factor analysis using the number of streamlines among brain regions relevant to sensorimotor function. We used regression models to estimate the predictive value of sensorimotor network connectivity for hand grip performance measures while controlling for stroke lesion volumes. Each hand grip performance measure correlated with the connectivity of distinct brain sensorimotor networks. These results suggest that different brain networks may be responsible for different aspects of hand grip performance, which leads to varying clinical presentations of upper extremity impairment following stroke. Understanding the brain network correlates for different hand grip performances may facilitate the development of personalized rehabilitation interventions to directly target the responsible brain network for specific impairments in individual patients, thus improving outcomes.

Abstract Balance perturbations are often used to gain insight into reactive control strategies used to prevent falls. We developed a perturbation platform system (PPS) that can induce perturbations in both vertical and angled directions. The PPS was evaluated using human subject testing to verify its function and performance. The final system consisted of two box platforms that can individually perform vertical and angled surface perturbations. Following a perturbation, the system can automatically reset for the next iteration under the weight of the standing participant. The PPS achieves a peak downward acceleration of 4.4 m/s2 during drop events that simulate sudden surface changes. The experimental testing revealed that the perturbation induced a peak limb loading of 280 ± 38% of body weight (BW) during vertical drops and that participants' center of mass displacements were consistent with previous balance studies evaluating vertical perturbations. The system can be used in a laboratory or clinical setting to better understand balance response and control mechanisms and assist in rehabilitation training to improve balance control and help mitigate the incidence of falls.