Adherence to Simple Spring-Mass Mechanics During Submaximal Running in Individuals With Unilateral Transfemoral Amputation

Lower extremities adhering to the spring mechanics proposed by the spring-loaded inverted pendulum (SLIP) model during running are regarded as a form of running-gait optimization among runners. We examined the degree of adherence between experimental and SLIP model-predicted vertical ground reaction force (vGRF) in individuals with unilateral transfemoral amputation. Nine individuals with unilateral transfemoral amputation performed running trials at 6 different speeds on an instrument treadmill. The trials were set at 30% to 80% of their maximum speeds with a 10% increment. The experimental vGRF collected was compared with SLIP model-predicted vGRF. The degree of adherence was calculated using the R2 goodness-of-fit statistics. The experimental vGRF of the affected limbs exhibited a significantly higher degree of adherence than unaffected limbs. There were no significant differences in the degree of adherence between different speed trials for either limb. This finding indicates that running-specific prostheses exhibit mechanical behavior that is consistent with SLIP mechanics, whereas the unaffected limb relies on compensatory, non-SLIP-like strategies. Furthermore, the results suggest that the interaction of running-specific prostheses with other prosthetic components and the residual limb enables the preservation of running mechanics across a range of speeds, thereby supporting the application of SLIP-based modeling to the affected limb.