RESUMEN

Adaptive locomotion is an essential behavior for animals to survive. The central pattern generator in the spinal cord is responsible for the basic rhythm of locomotion through sensory feedback coordination, resulting in energy-efficient locomotor patterns. Individuals with symmetrical body proportions exhibit an energy-efficient symmetrical gait on flat ground. In contrast, individuals with lower limb amputation, who have morphologically asymmetrical body proportions, exhibit asymmetrical gait patterns. However, it remains unclear how the nervous system adjusts the control of the lower limbs. Thus, in this study, we investigated how individuals with unilateral transtibial amputation control their left and right lower limbs during locomotion using a two-dimensional neuromusculoskeletal model. The model included a musculoskeletal model with 7 segments and 18 muscles, as well as a neural model with a central pattern generator and sensory feedback systems. Specifically, we examined whether individuals with unilateral transtibial amputation acquire prosthetic gait through a symmetric or asymmetric feedback control for the left and right lower limbs. After acquiring locomotion, the metabolic costs of transport and the symmetry of the spatiotemporal gait factors were evaluated. Regarding the metabolic costs of transportation, the symmetric control model showed values approximately twice those of the asymmetric control model, whereas both scenarios showed asymmetry of spatiotemporal gait patterns. Our results suggest that individuals with unilateral transtibial amputation can reacquire locomotion by modifying sensory feedback parameters. In particular, the model reacquired reasonable locomotion for activities of daily living by re-searching asymmetric feedback parameters for each lower limb. These results could provide insight into effective gait assessment and rehabilitation methods to reacquire locomotion in individuals with unilateral transtibial amputation.

RESUMEN

The ability to sustain steady straight-ahead walking is one goal of gait rehabilitation for individuals with unilateral above-knee (UAK) amputation. Despite the morphological and musculoskeletal asymmetry resulting from unilateral limb loss, the mediolateral ground-reaction-impulse (GRI) should be counterbalanced between the affected and unaffected limbs during straight-ahead walking. Therefore, we investigated the strategies of mediolateral ground-reaction-force (GRF) generation adopted by UAK prosthesis users walking along a straight path. GRFs of 15 participants with UAK amputation were measured during straight-ahead walking. Then, the mediolateral GRI, stance time, and mean mediolateral GRF during the stance phase of the affected and unaffected limbs were compared. To better understand the GRF generation strategy, statistical-parametric-mapping (SPM) was applied to assess the phase-dependent difference of the mediolateral GRFs between two limbs. The results showed that UAK prosthesis users can achieve symmetric mediolateral GRI during straight-ahead walking by adopting an asymmetric gait strategy: shorter stance time and higher mean mediolateral GRF over the stance phase for the affected than for the unaffected limb. In addition, the analysis using SPM revealed that the affected limb generates a higher mean medial GRF component than the unaffected limb, especially during the single-support phase. Thus, a higher medial GRF during the single-support phase of the affected limb may allow UAK prosthesis users to achieve mediolateral GRI that are similar to those of the unaffected limb. Further insights on these mechanics may serve as guidelines on the improved design of prosthetic devices and the rehabilitation needs of UAK prosthesis users.

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RESUMEN

Carbon-fiber running-specific prostheses have enabled individuals with lower extremity amputation to run by providing a spring-like leg function in their affected limb. When individuals without amputation run at a constant speed on level ground, the net external mechanical work is zero at each step to maintain a symmetrical bouncing gait. Although the spring-like "bouncing step" using running-specific prostheses is considered a prerequisite for running, little is known about the underlying mechanisms for unilateral transfemoral amputees. The aim of this study was to investigate external mechanical work at different running speeds for unilateral transfemoral amputees wearing running-specific prostheses. Eight unilateral transfemoral amputees ran on a force-instrumented treadmill at a range of speeds (30, 40, 50, 60, 70, and 80% of the average speed of their 100-m personal records). We calculated the mechanical energy of the body center of mass (COM) by conducting a time-integration of the ground reaction forces in the sagittal plane. Then, the net external mechanical work was calculated as the difference between the mechanical energy at the initial and end of the stance phase. We found that the net external work in the affected limb tended to be greater than that in the unaffected limb across the six running speeds. Moreover, the net external work of the affected limb was found to be positive, while that of the unaffected limb was negative across the range of speeds. These results suggest that the COM of unilateral transfemoral amputees would be accelerated in the affected limb's step and decelerated in the unaffected limb's step at each bouncing step across different constant speeds. Therefore, unilateral transfemoral amputees with passive prostheses maintain their bouncing steps using a limb-specific strategy during running.

RESUMEN

As a fundamental motor pattern, the ability to run at a range of constant speeds is a prerequisite for participating in competitive games and recreational sports. However, it remains unclear how unilateral transfemoral amputees modulate anterior and posterior ground reaction force impulses (GRFIs) in order to maintain constant running speeds. The purpose of this study was to investigate anterior and posterior GRFIs across a wide range of constant running speeds in unilateral transfemoral amputees wearing a running-specific prosthesis. Eleven runners with unilateral transfemoral amputation ran on an instrumented treadmill at 5 different speeds (30%, 40%, 50%, 60%, and 70% of the average velocity of their 100-m personal records). Anterior-posterior ground reaction forces (GRFs) were measured at 1000 Hz over 14 consecutive steps. Impulse, magnitude, and duration of anterior and posterior GRFs were compared between the affected and unaffected limbs at each speed. The net anterior-posterior GRFI, reflecting the changes in horizontal running velocity, was consistently positive (propulsion) in the affected limb and negative (braking) in the unaffected limb at all speeds. Regardless of running speed, unilateral transfemoral amputees maintain constant running speeds not over each step, but over 2 consecutive steps (i.e., one stride).

RESUMEN

BACKGROUND: Running with prostheses has become a common activity for amputees participating in sports and recreation. However, very few studies have characterized the kinematic and kinetic parameters of walking in individuals with amputation who are runners. Thus, this study attempts to elucidate the kinematics and kinetics of walking in runners with a unilateral transfemoral amputation or knee-disarticulation. METHODS: This study experimentally compares the prosthetic and intact limbs of runners with prostheses as well as compares the findings against the limbs of age-matched able-bodied individuals while walking. Fourteen runners with a unilateral transfemoral amputation or knee-disarticulation were recruited and 14 age-matched able-bodied individuals were prepared using gait database. Spatiotemporal, kinematic, and kinetic parameters of walking were analyzed using a 3-demensional motion capture system. RESULTS: The results showed that the peak ankle positive power at pre-swing and peak hip positive power from loading response to mid stance in the intact limb were significantly larger than that in the prosthetic limb. Moreover, to compensate for missing anatomical functions on the prosthetic limb, it appeared that the intact limb of the runners generated larger peak joint power by producing more ankle plantarflexor and hip extensor moments while walking. INTERPRETATION: This study demonstrated that the runners rely on their intact limb while walking. Training of hip extensor muscles of the intact limb may be beneficial for these individuals.

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BACKGROUND: Understanding the potential risks of running-related injuries in unilateral transfemoral amputees contributes to the development and implementation of the injury prevention programme in running gait rehabilitation. We investigated the vertical ground reaction force loading in unilateral transfemoral amputees who used running-specific prostheses across a range of running speeds. METHODS: Ten unilateral transfemoral amputees and ten non-amputees performed running trials on an instrumented treadmill at the incremental speeds of 30, 40, 50, and 60% of their maximum acquired speeds. Per-step and cumulative vertical instantaneous loading rates were calculated from the vertical ground reaction force in the affected, unaffected, and non-amputated control limbs. FINDINGS: Both the per-step and cumulative vertical instantaneous loading rates of the unaffected limbs in runners with unilateral transfemoral amputation were significantly greater than the affected and non-amputated control limbs at all speeds. INTERPRETATION: The results of the present study suggest that runners with unilateral transfemoral amputation may be exposed to a greater risk of running-related injuries in their unaffected limbs compared to the affected and non-amputated control limbs.

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Carbon fiber running-specific prostheses have allowed lower extremity amputees to participate in running activity by providing spring-like properties in their affected limb. It has been established that as running speed increases, stiffness of the leg spring (leg stiffness; kleg) remains constant in non-amputees. Although a better understanding of kleg regulation may be helpful for the development of spring-based prostheses, little is known about stiffness regulation in unilateral transfemoral amputees. The aim of this study was to investigate stiffness regulation at different running speeds in unilateral transfemoral amputees wearing a running-specific prosthesis. Nine unilateral transfemoral amputees performed running on an instrumented treadmill across a range of speeds (30, 40, 50, 60, and 70% of their maximum running speed). Using a spring-mass model, kleg was calculated as the ratio of maximal vertical ground reaction force to maximum leg compression during the stance phase in both affected and unaffected limbs. We found a decrease in kleg from the slower speed to 70% speed for the affected limb, whereas no change was present in the unaffected limb. Specifically, there was a significant differences in the kleg between 30% and 70%, 40% and 70%, and 50% and 70%, and the magnitude of the kleg difference between affected and unaffected limbs varied with variations in running speeds in unilateral TFAs with an RSP. These results suggest the kleg regulation strategy of unilateral transfemoral amputees is not the same in the affected and unaffected limbs across a range of running speeds.

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To understand the step characteristics during sprinting in lower-extremity amputees using running-specific prosthesis, each athlete should be investigated individually. Theoretically, sprint performance in a 100-m sprint is determined by both step frequency and step length. The aim of the present study was to investigate how step frequency and step length correlate with sprinting performance in elite unilateral transtibial amputees. By using publicly-available Internet broadcasts, the authors analyzed 88 races from 7 unilateral transtibial amputees. For each sprinter's run, the average step frequency and step length were calculated using the number of steps and official race time. Based on Pearson's correlation coefficients between step frequency, step length, and official race time for each individual, the authors classified each individual into 3 groups: step-frequency reliant, step-length reliant, and hybrid. It was found that 2, 2, and 3 sprinters were classified into step-frequency reliant, step-length reliant, and hybrid, respectively. These results suggest that the step frequency or step length reliance during a 100-m sprint is an individual occurrence in elite unilateral transtibial amputees using running-specific prosthesis.

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Understanding the characteristics of ground reaction forces (GRFs) on both limbs during sprinting in unilateral amputees wearing running-specific prostheses would provide important information that could be utilized in the evaluation of athletic performance and development of training methods in this population. The purpose of this study was to compare GRFs between intact and prosthetic limbs during sprinting in unilateral transfemoral amputees wearing running-specific prostheses. Nine sprinters with unilateral transfemoral amputation wearing the same type of prosthesis performed maximal sprinting on a 40-m runway. GRFs were recorded from 7 force plates placed in the center of the runway. Peak forces and impulses of the GRFs in each direction were compared between limbs. Peak forces in vertical, braking, propulsive, and medial directions were significantly greater in intact limbs than those in prosthetic limbs, whereas there were no significant differences in peak lateral force between limbs. Further, significantly less braking impulses were observed in prosthetic limbs than in intact limbs; however, the other measured impulses were not different between limbs. Therefore, the results of the present study suggest that limb-specific rehabilitation and training strategies should be developed for transfemoral amputees wearing running-specific prostheses.

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