Purpose: To investigate the joint-specific contributions to the total lower-extremity joint work during a prolonged fatiguing run.
Methods: Recreational long-distance runners (n = 13) and competitive long-distance runners (n = 12) performed a 10-km treadmill run with near-maximal effort. A three-dimensional motion capture system synchronized with a force-instrumented treadmill was used to calculate joint kinetics and kinematics of the lower extremity in the sagittal plane during the stance phase at 13 distance points over the 10-km run.
Results: A significant (P < 0.05) decrease of positive ankle joint work as well as an increase of positive knee and hip joint work was found. These findings were associated with a redistribution of the individual contributions to total lower-extremity work away from the ankle toward the knee and hip joint which was more distinctive in the recreational runner group than in the competitive runner group. This redistribution was accomplished by significant (P < 0.05) reductions of the external ground-reaction force lever arm and joint torque at the ankle and by the significant (P < 0.05) increase of the external ground-reaction force lever arm and joint torque at the knee and hip.
Conclusions: The redistribution of joint work from the ankle to more proximal joints might be a biomechanical mechanism that could partly explain the decreased running economy in a prolonged fatiguing run. This might be because muscle-tendon units crossing proximal joints are less equipped for energy storage and return compared with ankle plantar flexors and require greater muscle volume activation for a given force. To improve running performance, long-distance runners may benefit from an exercise-induced enhancement of ankle plantar flexor muscle-tendon unit capacities.