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TRANSLATIONAL PHYSIOLOGY

Effects of depletion exercise and light training on muscle glycogen supercompensation in men

¹Naval Health Research Center, San Diego, California 92186; ²Departments of Internal Medicine and ³Cellular and Molecular Physiology, and ⁴Howard Hughes Medical Institute, Yale University, School of Medicine, New Haven, Connecticut 06510; and ⁵GEO-CENTERS, Inc., Newton, Massachusetts 02459

Submitted 8 May 2003 ; accepted in final form 29 July 2003

Supercompensated muscle glycogen can be achieved by using several carbohydrate (CHO)-loading protocols. This study compared the effectiveness of two "modified" CHO-loading protocols. Additionally, we determined the effect of light cycle training on muscle glycogen. Subjects completed a depletion (D, n = 15) or nondepletion (ND, n = 10) CHO-loading protocol. After a 2-day adaptation period in a metabolic ward, the D group performed a 120-min cycle exercise at 65% peak oxygen uptake (O_{2 peak}) followed by 1-min sprints at 120% O_{2 peak} to exhaustion. The ND group performed only 20-min cycle exercise at 65% O_{2 peak}. For the next 6 days, both groups ate the same high-CHO diets and performed 20-min daily cycle exercise at 65% O_{2 peak} followed by a CHO beverage (105 g of CHO). Muscle glycogen concentrations of the vastus lateralis were measured daily with ¹³C magnetic resonance spectroscopy. On the morning of day 5, muscle glycogen concentrations had increased 1.45 (D) and 1.24 (ND) times baseline (P < 0.001) but did not differ significantly between groups. However, on day 7, muscle glycogen of the D group was significantly greater (p < 0.01) than that of the ND group (130 ± 7 vs. 104 ± 5 mmol/l). Daily cycle exercise decreased muscle glycogen by 10 ± 2 (D) and 14 ± 5 mmol/l (ND), but muscle glycogen was equal to or greater than preexercise values 24 h later. In conclusion, a CHO-loading protocol that begins with a glycogen-depleting exercise results in significantly greater muscle glycogen that persists longer than a CHO-loading protocol using only an exercise taper. Daily exercise at 65% O_{2 peak} for 20 min can be performed throughout the CHO-loading protocol without negatively affecting muscle glycogen supercompensation.

carbohydrate loading; detraining; ¹³C magnetic resonance spectroscopy

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