CHANGES IN MAGNETIC-RESONANCE IMAGES IN HUMAN SKELETAL-MUSCLE AFTER ECCENTRIC EXERCISE

To investigate the time-course of changes in transverse relaxation tim e (T-2) and cross-sectional area (CSA) of the quadriceps muscle after a single session of eccentric exercise, magnetic resonance imaging was performed on six healthy male volunteers before and at 0, 7, 15, 20, 30 and 60 min and 12, 24, 36, 48, 72 and 168 h after exercise. Althoug h there was almost no muscle soreness immediately after exercise, it s tarted to increase 1 day after, peaking 1-2 days after the exercise (P <0.01). Immediately after exercise, T-2 increased significantly in the rectus femoris, vastus lateralis and intermedius muscles (P<0.05) and decreased quickly continuing until 60 min after exercise. At and afte r the 12th h, a significant increase was perceived again in the T-2 va lues of the vastus lateralis and intermedius muscles (P<0.01) [maximum 9.3 (SEM 2.8)% and 10.9 (SEM 2.2)%, respectively]. The maximal values were exhibited at 24-36 h after exercise. In contrast, the rectus fem oris muscle showed no delayed-stage increase. Also, in CSA, an increas e after 12 h was observed in addition to the one immediately after exe rcise in the vastus lateralis, intermedius and medialis and quadriceps muscles as a whole (P<0.01), reaching the maximal values at 12-24 h a fter exercise. The plasma creatine kinase activity remained unchanged up to 24 h after and then increased significantly 48 h after exercise (P<0.05). Beginning 12 h after exercise, the subjects whose T-2 and CS A increased less than the others displayed a faster decrease in muscle soreness. These results suggested that T-2 and CSA displayed bimodal responses after eccentric exercise and the time-courses of changes in them were similar to those in muscle soreness.