MULTIPARAMETRIC CLASSIFICATION OF MUSCLE T-1 AND T-2 RELAXATION-TIMESDETERMINED BY MAGNETIC-RESONANCE-IMAGING - THE EFFECTS OF DYNAMIC EXERCISE IN TRAINED AND UNTRAINED SUBJECTS

Muscle relaxation times can now be measured accurately with magnetic r esonance imaging (MRI), distinguishing working muscles from non-workin g muscles. A correlation between T-2 increase and work intensity has b een shown in healthy volunteers. The small amount of data on T-1 relax ation times is contradictory. In addition, all the published studies h ave concerned short-duration exercise in subjects of unknown training level. The goals of this study were (i) to determine T-1 and T-2, vari ations in thigh muscles after long dynamic exercise, (ii) to analyse t he effects of training and (iii) to determine the relationship between power output and relaxation times after exercise. Sedentary men, socc er players and triathletes performed submaximal dynamic exercise at a constant heart rate for 15 min. MRI was performed before and 5 min aft er the end of exercise. The results showed (i) that T-1 increased in p arallel to T-2 in anterior thigh muscles and (ii) that multiple corres pondence analysis and hierarchical ascending classification can discri minate three subject classes according to power output, training level and relaxation times, which fitted well with our three groups of subj ects.