T2 mapping of muscle activation during single-leg vertical jumping exercise

This study investigated using elevation of the spin-spin relaxation time (T2) in magnetic resonance imaging (MRI) to map recruitment differences in the thigh and calf between two distinct populations during single-leg jumping. Twelve healthy subjects formed two groups based on jumping ability. Subjects took a maximal exercise test (MET) to determine aerobic fitness. Subjects performed 5x10 single-leg jumps at body weight (Post1) and at body weight+33% (Post2) on a force platform while wearing a weighted vest at Post2. Performance was determined as concentric jumping power normalized to the subject's maximum aerobic power. Spin echo MRI at Baseline, Post1 and Post2 determined muscle activation as the percentage of muscle pixels with elevated T2 after exercise. A novel metric based on the performance/activation ratio highlighted recruitment efficiency differences between groups. Results suggest that recruitment efficiency throughout the lower limb (especially suppression of co-activating antagonists) was the dominant factor in enhancing jumping performance.