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

• Published in: European journal of applied physiology Vol. 115; no. 9; pp. 1919 - 1926
• Main Authors: Fernández-Elías, Valentín E., Ortega, Juan F., Nelson, Rachael K., Mora-Rodriguez, Ricardo
• Format: Journal Article
• Language: English
• Published: Berlin/Heidelberg Springer Berlin Heidelberg 01.09.2015; Springer Nature B.V
• Subjects: Bicycling - physiology; Biomedical and Life Sciences; Biomedicine; Body Water - metabolism; Carbohydrates; Glycogen - metabolism; Heat-Shock Response - physiology; Hot Temperature; Human Physiology; Humans; Liver; Male; Muscle, Skeletal - physiology; Occupational Medicine/Industrial Medicine; Original Article; Physical Endurance - physiology; Recovery of Function - physiology; Sports Medicine; Young Adult; Carbohydrates; Muscle glycogen storage; Sweating; Muscle water; Oral rehydration
• ISSN: 1439-6319; 1439-6327
• DOI: 10.1007/s00421-015-3175-z

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 ( V ˙ O 2 max  = 54.4 ± 1.05 mL kg −1  min −1 ; mean ± SD) dehydrated 4.6 ± 0.2 % by cycling 150 min at 65 % V ˙ O 2 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.