Effects of prosthetic stiffness and added mass on metabolic power and asymmetry in female runners with a leg amputation

Abstract

Similar to non-amputees, female athletes with unilateral transtibial amputation (TTA) using running-specific leg prostheses (RSPs) may have worse running economy and higher rates of running-related injury than male athletes. Optimizing RSP configuration for female athletes could improve running economy and minimize biomechanical asymmetry, which has been associated with running-related injury. Nine females with a TTA ran at 2.5 m/s while we measured metabolic rates and ground reaction forces. Subjects used an RSP with a manufacturer-recommended stiffness category, one category less stiff and two categories less stiff than recommended. Use of an RSP two categories less stiff resulted in 3.0% lower net metabolic power (p=0.04), 7.8% lower affected leg stiffness (p=6.01x10-4), increased contact time asymmetry (p=0.04), and decreased stance average vertical ground reaction force asymmetry (p=0.04) compared to a recommended stiffness category RSP. Lower RSP stiffness (kN/m) values were associated with lower net metabolic power (p=0.02), lower affected leg stiffness (p=1.36x10-4), longer affected leg contact time (p=1.46x10-4) and similar affected leg peak and stance-average vertical ground reaction force compared to higher RSP stiffness values. Subjects then used the RSP stiffness category that elicited the lowest net metabolic power with 100 g, 200 g and 300 g added distally. We found no significant effects of added mass on net metabolic power, biomechanics, or asymmetry. These results suggest that female runners with a TTA could decrease metabolic power during running while minimizing biomechanical asymmetries, which have been associated with running-related injury using an RSP two categories less stiff than manufacturer recommended.