Relationship between muscle water and glycogen recovery after prolonged exercise in the heat in humans

PurposeIt is usually stated that glycogen is stored in human muscle bound to water in a proportion of 1:3 g. We investigated this proportion in biopsy samples during recovery from prolonged exercise.MethodsOn two occasions, nine aerobically trained subjects (V˙O2maxV˙O2max\dot{V}{\text{O}}_{2\hbox{max} } = 54.4 ± 1.05 mL kg−1 min−1; mean ± SD) dehydrated 4.6 ± 0.2 % by cycling 150 min at 65 % V˙O2maxV˙O2max\dot{V}{\text{O}}_{2\hbox{max} } in a hot-dry environment (33 ± 4 °C). One hour after exercise subjects ingested 250 g of carbohydrates in 400 mL of water (REHLOW) or the same syrup plus water to match fluid losses (i.e., 3170 ± 190 mL; REHFULL). Muscle biopsies were obtained before, 1 and 4 h after exercise.ResultsIn both trials muscle water decreased from pre-exercise similarly by 13 ± 6 % and muscle glycogen by 44 ± 10 % (P < 0.05). After recovery, glycogen levels were similar in both trials (79 ± 15 and 87 ± 18 g kg−1 dry muscle; P = 0.20) while muscle water content was higher in REHFULL than in REHLOW (3814 ± 222 vs. 3459 ± 324 g kg−1 dm, respectively; P