Effect of aerobic capacity on the T2 increase in exercised skeletal muscle

The increase in nuclear magnetic resonance transverse relaxation time (T2) of muscle water measured by magnetic resonance imaging after exercise has been correlated with work rate in human subjects. This study compared the T2 increase in thigh muscles of trained (cyclingV˙o 2 max = 54.4 ± 2.7 ml O2 · kg−1 · min−1, mean ± SE, n = 8, 4 female) vs. sedentary (31.7 ± 0.9 ml O2 · kg−1 · min−1, n = 8, 4 female) subjects after cycling exercise for 6 min at 50 and 90% of the subjects' individually determinedV˙o 2 max. There was no significant difference between groups in the T2 increase measured in quadriceps muscles within 3 min after the exercises, despite the fact that the absolute work rates were 60% higher in the trained group (253 ± 15 vs. 159 ± 21 W for the 90% exercise). In both groups, the increase in T2 of vastus muscles was twofold greater after the 90% exercise than after the 50% exercise. The recovery of T2 after the 90% exercise was significantly faster in vastus muscles of the trained compared with the sedentary group (mean recovery half-time 11.9 ± 1.2 vs. 23.3 ± 3.7 min). The results show that the increase in muscle T2varies with work rate relative to muscle maximum aerobic power, not with absolute work rate.