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J Appl Physiol 84: 1178-1184, 1998;
8750-7587/98 $5.00
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Vol. 84, Issue 4, 1178-1184, April 1998

Effect of muscle glycogen content on exercise-induced changes in muscle T2 times

Thomas B. Price and John C. Gore

Department of Diagnostic Radiology, Yale University School of Medicine, New Haven, Connecticut 06510

Effects of gastrocnemius glycogen (Gly) concentration on changes in transverse relaxation time (T2; ms) were studied after 5-min plantar flexion at 25% of maximum voluntary contraction (MVC). Gastrocnemius Gly, phosphorus metabolites, and T2 were measured in seven subjects by using interleaved 13C/31P magnetic resonance spectroscopy (MRS) at 4.7 T and magnetic resonance imaging (MRI; 1.5 T). After baseline MRS/MRI, subjects exercised for 5 min at 25% of MVC and were reexamined (MRS/MRI). Subjects then performed ~15 min of single-leg toe raises (50 ± 2% of MVC), depleting gastrocnemius Gly by 43%. After a 1-h rest (for T2 return to baseline), subjects repeated the 5-min protocol, followed by a final MRI/MRS. After the initial 5-min protocol, T2 values increased by 5.9 ± 0.8 ms (29.9 ± 0.4 to 35.8 ± 0.6 ms), whereas Gly did not change significantly (70.5 ± 6.8 to 67.6 ± 7.4 mM). After 15 min of toe raises, gastrocnemius Gly was reduced to 40.4 ± 5.3 mM (P <=  0.01), recovering to 45.8 ± 5.3 mM (P <= 0.05) during a 1-h rest. After the second 5-min bout of plantar flexion (reduced Gly at 25% of MVC), T2 values increased by 5.0 ± 0.8 ms (30.4 to 35.4 ms), whereas muscle Gly rose to 57.6 ± 5.3 mM. We conclude that muscle Gly concentration per se does not affect exercise-induced T2 increases in the human gastrocnemius.

transverse relaxation time; magnetic resonance imaging; spectroscopy


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