Leg stiffness and sprint ability in amputee sprinters.

Background: Understanding leg stiffness (K-leg) in amputee sprinters is important for the evaluation of their sprint ability and development of running-specific prostheses (RSP). Objectives: To investigate K-leg during hopping in amputee sprinters. Study Design: Cross-sectional study. Methods: Seven transtibial (TT) and seven transfemoral (TF) amputee sprinters, as well as seven non-active able-bodied subjects, performed one-legged hopping matching metronome beats at 2.2 Hz. Amputees hopped on their sound limb whereas able-bodied (AB) subjects hopped on their dominant limb. Using a spring-mass model, K-leg was calculated from the subjects' body mass, ground contact and flight times. Results: Both TT and TF sprinters demonstrated significantly higher K-leg than AB subjects. K-leg during hopping on the sound leg significantly correlated with personal records attained in a 100-m sprint in both TT (r = -0.757) and TF sprinters (r = -0.855). Conclusion: The results of the present study suggest that amputee sprinters have a greater K-leg during hopping than inactive non-amputees, and that their sprint ability can be predicted from the K-leg during hopping at 2.2 Hz on the sound limb.