Effects of exercise on muscle transverse relaxation determined by MR imaging and in vivo relaxometry

Abstract

The purpose of this study was to determine the effects of intense exercise on the proton transverse (T2) relaxation of human skeletal muscle. The flexor digitorium profundus muscles of 12 male subjects were studied by using magnetic resonance imaging (MRI; 6 echoes, 18-ms echo time) and in vivo magnetic resonance relaxometry (1,000 echoes, 1.2-ms echo time), before and after an intense handgrip exercise. MRI of resting muscle produced a single T2 value of 32 ms that increased by 19% ( P < 0.05) with exercise. In vivo relaxometry showed at least three T2 components (>5 ms) for all subjects with mean values of 21, 40, and 137 ms and respective magnitudes of 34, 49, and 14% of the total magnetic resonance signal. These component magnitudes changed with exercise by −44% ( P < 0.05), +52% ( P < 0.05), and +23% ( P < 0.05), respectively. These results demonstrate that intense exercise has a profound effect on the multicomponent T2 relaxation of muscle. Changes in the magnitudes of all the T2 components synergistically increase MRI T2, but changes in the two shortest T2components predominate.