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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 ([Formula: see text] = 54.4 ± 1.05 mL kg(-1) min(-1); mean ± SD) dehydrated 4.6 ± 0.2 % by cycling 150 min at 65 % [Formula: see text] 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., 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 REHFULL than in REHLOW (3814 ± 222 vs. 3459 ± 324 g kg(-1) dm, respectively; P < 0.05; ES = 1.06). Despite the insufficient water provided during REHLOW, per each gram of glycogen, 3 g of water was stored in muscle (recovery ratio 1:3) while during REHFULL 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 REHFULL) likely due to water storage not bound to glycogen.

The aim of this study was to investigate the relevance of individual characteristics for thermoregulation during prolonged cycling in the heat. For this purpose, 28 subjects cycled for 60 min at 60% VO(2peak) in a hot-dry environment (36 ± 1°C; 25 ± 2% relative humidity, airflow 2.5 m/s). Subjects had a wide range of body mass (99-43 kg), body surface area (2.2-1.4 m(2)), body fatness (28-5%) and aerobic fitness level (VO(2peak) = 5.0-2.1 L/min). At rest and during exercise, rectal and mean skin temperatures were measured to calculate the increase in body temperature (ΔT (body)) during the trial. Net metabolic heat production (M (NET)) and potential heat loss (by means of evaporation, radiation and convection) were calculated. Although subjects exercised at the same relative intensity, ΔT (body) presented high between-subjects variability (range from 0.44 to 1.65°C). ΔT (body) correlated negatively with body mass (r = -0.49; P < 0.01), body surface area (r = -0.47; P < 0.01) and T(body) at rest (r = -0.37; P < 0.05), but it did not significantly correlate with body fatness (r = 0.12; P > 0.05). ΔT (body) positively correlated with the body surface area/mass ratio (r = 0.46; P < 0.01) and the difference between M (NET) and potential heat loss (r = 0.56; P < 0.01). In conclusion, a large body size (mass and body surface area) is beneficial to reduce ΔT (body) during cycling exercise in the heat. However, subjects with higher absolute heat production (more aerobically fit) accumulate more heat because heat production may exceed potential heat loss (uncompensability).