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

The purpose of this study was to determine the effects of intense exercise on the proton transverse (Ta) relaxation of human skeletal muscle. The flex or digitorium profundus muscles of 12 male subjects were studied by using m agnetic resonance imaging (MRI; 6 echoes, 18-ms echo time) and in vivo magn etic resonance relaxometry (1,000 echoes, 1.2-ms echo time), before and aft er an intense handgrip exercise. MRI of resting muscle produced a single T- 2 value of 32 ms that increased by 19% (P < 0.05) with exercise. In vivo re laxometry showed at least three T-2 components (> 5 ms) for all subjects wi th mean values of 21, 40, and 137 ms and respective magnitudes of 34, 49, a nd 14% of the total magnetic resonance signal. These component magnitudes c hanged 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 p rofound effect on the multicomponent T-2 relaxation of muscle. Changes in t he magnitudes of all the T-2 components synergistically increase MRI T-2, b ut changes in the two shortest T-2 components predominate.