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

The increase in nuclear magnetic resonance transverse relaxation time (T-2) of muscle water measured by magnetic resonance imaging after exercise has been correlated with work rate in human subjects. This study compared the T-2 increase in thigh muscles of trained (cycling (V) over dot(2 max) = 54.4 +/- 2.7 ml O-2 . kg(-1) . min(-1), mean +/- SE, n = 8, 4 female) vs. sedentary (31.7 +/- 0.9 ml O-2 . kg(-1) . min(-1), n = 8, 4 female) subjects after cycling exercise for 6 min at 50 and 90% of the subjects' individually determined (V) over dot(2 max). There was no significant difference between groups in the T-2 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 T-2 of vastus muscles was twofold greater after the 90% exercise than after the 50% exercise. The recovery of T-2 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 T-2 varies with work rate relative to muscle maximum aerobic power, not with absolute work rate.