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

Abstract

Purpose

It 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.

Methods

On two occasions, nine aerobically trained subjects ($\dot{V}{\text{O}}_{2\hbox{max} }$ = 54.4 ± 1.05 mL kg⁻¹ min⁻¹; mean ± SD) dehydrated 4.6 ± 0.2 % by cycling 150 min at 65 % $\dot{V}{\text{O}}_{2\hbox{max} }$ in a hot-dry environment (33 ± 4 °C). One hour after exercise subjects ingested 250 g of carbohydrates in 400 mL of water (REH_LOW) or the same syrup plus water to match fluid losses (i.e., 3170 ± 190 mL; REH_FULL). Muscle biopsies were obtained before, 1 and 4 h after exercise.

Results

In 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 REH_FULL than in REH_LOW (3814 ± 222 vs. 3459 ± 324 g kg⁻¹ dm, respectively; P < 0.05; ES = 1.06). Despite the insufficient water provided during REH_LOW, per each gram of glycogen, 3 g of water was stored in muscle (recovery ratio 1:3) while during REH_FULL this ratio was higher (1:17).

Conclusions

Our findings agree with the long held notion that each gram of glycogen is stored in human muscle with at least 3 g of water. Higher ratios are possible (e.g., during REH_FULL) likely due to water storage not bound to glycogen.