Joint angle-torque characteristics of the knee extensors following eccentric exercise-induced muscle damage in young, active women

Functional disruption following eccentric exercise-induced muscle damage is characterized by an immediate and prolonged loss in force-generating capacity, a disproportionate loss of strength at short muscle lengths, and a rightward shift in muscle length-tension relationship, in favor of a longer muscle length for optimal force generation. The purpose of this study was to examine progressive changes in muscle joint angle-torque characteristics following strenuous eccentric exercise in the quadriceps group, in female athletes. Seventeen physically active female athletes completed eccentric exercise designed to induce muscle damage. Isokinetic dynamometry was used to determine characteristics of muscle strength loss for the following dependant variables: change in maximal force, force at optimal and short muscle lengths, and shift in length-tension relationship at 1 hour, 24 hours, 48 hours, 72 hours, and 96 hours following damaging exercise. Perceived soreness and creatine kinase activity were also measured at these times. Significant increases in perceived soreness and creatine kinase activity, and a significant reduction in force-generating capacity were observed. A greater strength loss at short muscle lengths was observed following damaging exercise [17.2% vs. 25.7% relative force reduction for optimal and short (71° and 21° from full extension) muscle lengths, respectively]. A significant rightward shift in optimal joint angle for force generation was also observed, indicating that maximal force was generated at a longer muscle length subsequent to damaging exercise. This paper demonstrates a progressive rightward shift in the muscle length tension relationship.