Effect of asymmetric crank arm lengths on performance-related variables in cyclists with an anatomical lower limb length discrepancy

The aim of this study was to evaluate the effects of using asymmetric crank arms in cyclists affected by an inequality in lower limb length. Three male cyclists with a lower limb length difference of 28, 14, and 10 mm performed three experimental test sessions separated by 5 days, which were conducted using three different crank arm length conditions (170 mm for the long lower limb and 170, 165, and 160 mm for the short lower limb). Each test session included one 8-min pedalling exercise at 60% of maximal power output, two 10-s sprints, and one 30-s Wingate test. Power output was assessed during the supra-maximal exercises; while, physiological (heart rate, oxygen consumption, gross efficiency, and cycling economy) and biomechanical (hip, knee and ankle 2D kinematics) variables were measured during the submaximal exercises. Perceived exertion and perceived comfort were evaluated during all pedalling exercises. The results showed that the shortening of the crank length for the short lower limb (160 and 165 vs. 170 mm) reduced the knee and ankle extension and the hip and knee range of motion. In addition, the maximal power output and the perceived comfort were improved, while the perceived exertion was reduced. Therefore, the use of asymmetric crank arms during cycling could compensate for lower limb length discrepancy by modifying joint kinematics and by improving performance and perceived comfort.