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Understanding the sprinting patterns of individuals with unilateral transfemoral amputation (uTFA) is important for designing improved running-specific prostheses and for prosthetic gait rehabilitation. Continuous relative phase (CRP) analysis acquires clues from movement kinematics and obtains insights into the sprinting coordination of individuals with uTFA. Seven individuals with uTFA sprinted on a 40 m runway. The spatio-temporal parameters, joint and segment angles of the lower limbs were obtained, and CRP analysis was performed on thigh-shank and shank-foot couplings. Subsequently, the asymmetry ratios of the parameters were calculated. Statistical analyses were performed between the lower limbs. Significant differences in the stance time, stance phase percentage, ankle joint angles and CRP of the shank-foot coupling (p < 0.05) were observed between the lower limbs. The primary contributor to these differences could be the structural differences between the lower limbs. Despite the presence of different coordination features in the stance and swing phases between the lower limbs, no significant difference in the coordination patterns of the thigh-shank coupling was observed. This may be a compensation strategy for achieving coordination patterns with improved symmetry between the lower limbs. The results of this study provide novel insights into the sprinting movement patterns of individuals with uTFA.

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BACKGROUND: Individuals with unilateral transfemoral amputation are prone to developing health conditions such as knee osteoarthritis, caused by additional loading on the intact limb. Such individuals who can run again may be at higher risk due to higher ground reaction forces (GRFs) as well as asymmetric gait patterns. The two aims of this study were to investigate manipulating step frequency as a method to reduce GRFs and its effect on asymmetric gait patterns in individuals with unilateral transfemoral amputation while running. METHODS: This is a cross-sectional study. Nine experienced track and field athletes with unilateral transfemoral amputation were recruited for this study. After calculation of each participant's preferred step frequency, each individual ran on an instrumented treadmill for 20 s at nine different metronome frequencies ranging from - 20% to + 20% of the preferred frequency in increments of 5% with the help of a metronome. From the data collected, spatiotemporal parameters, three components of peak GRFs, and the components of GRF impulses were computed. The asymmetry ratio of all parameters was also calculated. Statistical analyses of all data were conducted with appropriate tools based on normality analysis to investigate the main effects of step frequency. For parameters with significant main effects, linear regression analyses were further conducted for each limb. RESULTS: Significant main effects of step frequency were found in multiple parameters (P < 0.01). Both peak GRF and GRF impulse parameters that demonstrated significant main effects tended towards decreasing magnitude with increasing step frequency. Peak vertical GRF in particular demonstrated the most symmetric values between the limbs from - 5% to 0% metronome frequency. All parameters that demonstrated significant effects in asymmetry ratio became more asymmetric with increasing step frequency. CONCLUSIONS: For runners with a unilateral transfemoral amputation, increasing step frequency is a viable method to decrease the magnitude of GRFs. However, with the increase of step frequency, further asymmetry in gait is observed. The relationships between step frequency, GRFs, and the asymmetry ratio in gait may provide insight into the training of runners with unilateral transfemoral amputation for the prevention of injury.

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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.

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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).

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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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CONTEXT: In sprint events, the first 2 steps are used to accelerate the center of mass horizontally and vertically. Amputee athletes cannot actively generate energy with their running-specific prosthesis. It is likely that sprint acceleration mechanics, including step asymmetry, are altered compared with able-bodied athletes. PURPOSE: To investigate spatiotemporal and kinetic variables of amputee compared with able-bodied sprinters. METHODS: Kinematic and kinetic data of the first and second stance were collected from 15 able-bodied and 7 amputee sprinters (2 unilateral transfemoral, 4 unilateral transtibial, and 1 bilateral transtibial) with a motion-capture system (250 Hz) and 2 force plates (1000 Hz). In addition, bilateral asymmetry was quantified and compared between groups. RESULTS: Compared with able-bodied athletes, amputee athletes demonstrated significantly lower performance values for 5- and 10-m times. Step length, step velocity, and step frequency were decreased and contact times increased. Peak horizontal force and relative change of horizontal velocity were decreased in both stances. Peak vertical force and relative change of vertical velocity were lower for the amputee than the able-bodied group during the first stance but significantly higher during the second stance. During the first stance, able-bodied and amputee sprinters displayed a similar orientation of the ground-reaction-force vector, which became more vertically orientated in the amputee group during second stance. Amputee sprinters showed significantly greater asymmetry magnitudes for vertical force kinetics compared with able-bodietd athletes. CONCLUSION: A running-specific prosthesis does not replicate the function of the biological limb well in the early acceleration phase.

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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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[Purpose] To verify the effects of sagittal plane alignment changes in running-specific transtibial prostheses on ground reaction forces (GRFs). [Subjects and Methods] Eight transtibial amputees who used running-specific prostheses during sprinting participated. The sprint movements were recorded using a Vicon-MX system and GRF measuring devices. The experiment levels were set as regularly recommended alignment (REG; the normal alignment for the subjects) and dorsiflexion or plantar flexion from the REG. [Results] The subjects were classified into fast (100-m personal best < 12.50 s) and slow (100-m personal best ≥ 12.50 s) groups. In both groups, there were no significant differences in the center of gravity speed; further, the difference in the stance time was significant in the slow group but not in the fast group. Significant differences were observed in the step length for the fast group, whereas the stance time and step rate significantly differed in the slow group. The GRF impulse showed significant differences in the vertical and braking directions in both groups. [Conclusion] The GRFs are affected by sagittal plane alignment changes in running-specific prostheses. Moreover, our results suggest that the change in GRFs along with the altered sagittal plane alignment influenced the step length and step rate.

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OBJECTIVES: (1) To test the validity of a trifilar pendulum in estimating moments of inertia (MOIs) for running-specific prostheses (RSPs), (2) to measure inertial properties (mass, center of mass [CM] position, and MOIs) for 4 RSPs, (3) to verify the influence of the stiffness on the inertial properties of RSPs, and (4) to develop a predictive equation to estimate RSP CM positions. DESIGN: An aluminum block with known MOIs was used for verifying the accuracy of the trifilar pendulum MOI measurements. MOI errors were investigated by systematically misaligning the block and pendulum principal axes across a range of 1 to 10cm. Mass, CM position, and MOI were tested across 4 RSP designs with 3 stiffness categories each. SETTING: University biomechanics laboratory. SPECIMENS: Four different RSP designs and 3 stiffness categories per design were examined. INTERVENTIONS: Not applicable. MAIN OUTCOME MEASURES: MOI errors from known values and principal axis misalignments between RSPs and pendulum; mass, CM positions, and RSP principal axis MOIs; and predictive equation CM position errors. RESULTS: The trifilar pendulum estimated MOIs within -6.21×10(-5)kg/m(2) (≤1% error) for a block with known MOIs. Misalignments of 1 to 5cm between the RSPs' and pendulum's CM yielded errors from .00002 to .00113 kg/m(2) (0.3%-59.2%). Each RSP's inertial properties are presented. MOIs about any axis varied <.004kg/m(2) across stiffness categories; MOIs differed up to .013kg/m(2) between different designs. The predictive CM equation erred between .010 and .028m when using average input values across an RSP design. CONCLUSIONS: Trifilar pendulums can accurately measure RSP MOI. The RSP inertial properties differed slightly across stiffness categories within each design, but differed more substantially across different RSP designs. Using a predictive equation to estimate RSP CM positions can provide adequate data, but directly measuring CM positions is preferable.

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