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Departments of 1 Physiology, 2 Radiology, and 3 Kinesiology, Michigan State University, East Lansing, Michigan 48824
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 (cycling
O2 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 determined
O2 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 T2
varies with work rate relative to muscle maximum aerobic power, not
with absolute work rate.
muscle recruitment; muscle functional magnetic resonance imaging; cycling exercise; transverse relaxation time
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