Effect of muscle glycogen content on exercise-induced changes in muscle T2 times.
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 approximately 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.
Price
T B
TB
Department of Diagnostic Radiology, Yale University School of Medicine, New Haven, Connecticut 06510, USA. price@boreas.med.yale.edu
Gore
J C
JC
D000293:Adolescent; D000328:Adult; D015444:Exercise / Q000502:physiology*; D005260:Female; D019298:Glucose-6-Phosphate / Q000378:metabolism; D006003:Glycogen / Q000378:metabolism*; D006801:Humans; D006863:Hydrogen-Ion Concentration; D008279:Magnetic Resonance Imaging; D009682:Magnetic Resonance Spectroscopy; D008297:Male; D009126:Muscle Relaxation / Q000502:physiology; D018482:Muscle, Skeletal / Q000378:metabolism*; D010725:Phosphocreatine / Q000378:metabolism; D013997:Time Factors
D010725:Phosphocreatine; D019298:Glucose-6-Phosphate; D006003:Glycogen