The Effect of Unequal Crank Arm Lengths and Cycling-Specific Prostheses for Recreational Riders with a Transtibial Amputation

Abstract

ABSTRACT Recreational cyclists with a transtibial amputation (TTA) exhibit kinematic and kinetic asymmetries between their biological and affected legs, which may worsen efficiency. Use of unequal crank arm lengths and/or a cycling-specific prosthesis (CSP) could reduce mechanical asymmetries and improve efficiency. Purpose We determined the effects of shorter affected side (AS) crank arm lengths and cycling with two different prostheses on joint and crank power, asymmetry, and net efficiency. Methods Twelve participants with a TTA rode at 1.5 W·kg−1 with equal (175 mm) and shorter AS crank arms (160, 165, 170 mm) using a daily-use prosthesis and CSP. We used statistical parametric mapping to determine differences in instantaneous joint and crank power between prostheses and linear mixed-effects models to compare average joint and crank power, asymmetry, and net efficiency. Results Shorter AS crank arm lengths reduced the magnitude of peak positive (P ≤ 0.001) and negative (P < 0.001) crank power on the AS. Use of a CSP increased the magnitude of peak positive knee power (P < 0.001) and decreased the magnitude of peak negative crank power (P < 0.001) on the AS compared with a daily-use prosthesis. Shorter AS crank arm lengths while using a CSP reduced average hip joint (P = 0.014) and hip transfer (P = 0.025) power asymmetry from 35% to 20% and 118% to 62%, respectively. However, we found no significant differences in AS average joint or crank power, knee joint or crank power asymmetry, or net efficiency. Conclusions Cycling at 1.5 W·kg−1 with unequal crank arm lengths and CSP improves hip joint power and hip transfer power asymmetry but does not alter crank asymmetry or net efficiency for recreational cyclists with a TTA.