Author(s): MACCHI, R., RAVEL, A., LAGOUTE, T., LACROIX, V., ROSSI, J., HUPIN, D., MILLET, G.Y., Institution: FLORALIS, Country: FRANCE, Abstract-ID: 2733

INTRODUCTION:
In order to run, individuals with lower-limb amputation need running-specific prostheses (RSP) designed to replicate the lower-limb mass–spring system [1]. Prosthesis stiffness is a key parameter [2,3] and is commonly selected solely based on body mass. However, this approach may be reductive, as optimal stiffness likely depends on individual running mechanics and slope conditions. This study aimed to investigate the influence of blade stiffness on running pattern and energy cost of running (Cr).
METHODS:
Sixteen unilateral transtibial amputee runners (13 males; 42.6 ± 11.7 y; 177.6 ± 9.1 cm; 71.7 ± 10.5 kg), habitual RSP users, completed 4-min treadmill trials at self-selected speed under three blade stiffness conditions: habitual (HAB), +1 (HARD), and −1 (SOFT) categories on level, uphill (+10%), and downhill (−10%) slopes. Comfort was assessed with a visual analog scale, and Cr was calculated from breath-by-breath V̇O₂ during the last minute. Spatiotemporal parameters and vertical and anteroposterior forces were measured on an instrumented treadmill. Kinematics for both limbs were recorded with 34 reflective markers, allowing prosthesis modelling and quantification of elastic energy storage and release angle. Linear mixed models assessed the effects of blade stiffness on all variables and the relationship between Cr and elastic energy release.
RESULTS:
No significant effect of blade stiffness on Cr was observed, although comfort was higher with the HAB blade compared to the HARD blade (p<0.05). In level running, only 29% of participants exhibited lower Cr with HAB, whereas this proportion increased to 62.5% during uphill running. A negative relationship (p<0.05) was found between Cr and elastic energy release, whereas no relationship was found between Cr and comfort. Blade stiffness had no effect on biomechanical parameters, except for a longer cycle time of the intact limb with the SOFT blade compared to HAB and HARD during uphill running (p<0.001). Regardless of blade stiffness, the intact limb showed greater vertical oscillation (p<0.05) and higher vertical peak and braking forces (p < 0.001), whereas propulsion force was higher for the amputee limb (p<0.001). Biomechanical asymmetry between limbs was influenced by slope (p<0.05).
CONCLUSION:
Although no effect of blade stiffness on energy cost was observed, substantial inter-individual variability suggests participant-specific responses that cannot be predicted from comfort perception. For many participants, the HAB blade was not the most economical, and slope affected the most efficient blade. Cr partly depends on elastic energy release, while stiffness has small effect on biomechanics running pattern or interlimb asymmetries. These findings indicate that body mass alone is insufficient to guide blade stiffness selection and the choice may differ between road and trail (graded) running.
REFERENCES
1. Nolan et al., Foot and Ankle Surgery, 2008
2. Beck et al., J Appl Physiol, 2017
3. Barnett et al., Gait & Posture, 2022