Multiparametric classification of muscle T1, and T2 relaxation times determined by magnetic resonance imaging. The effects of dynamic exercise in trained and untrained subjects

Muscle relaxation times can now be measured accurately with magnetic resonance imaging (MRI), distinguishing working muscles from non-working muscles. A correlation between T-2 increase and work intensity has been shown in healthy volunteers. The small amount of data on T-1 relaxation times is contradictory. In addition, all the published studies have concerned short-duration exercise in subjects of unknown training level. The goals of this study were (i) to determine T-1 and T-2, variations in thigh muscles after long dynamic exercise, (ii) to analyse the effects of training and (iii) to determine the relationship between power output and relaxation times after exercise. Sedentary men, soccer players and triathletes performed submaximal dynamic exercise at a constant heart rate for 15 min. MRI was performed before and 5 min after the end of exercise. The results showed (i) that T-1 increased in parallel to T-2 in anterior thigh muscles and (ii) that multiple correspondence analysis and hierarchical ascending classification can discriminate three subject classes according to power output, training level and relaxation times, which fitted well with our three groups of subjects.