Relationship between muscle water and glycogen recovery after prolonged exercise in the heat in humans.
OBJECTIVE
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.
Exercise Physiology Laboratory at Toledo, University of Castilla-La Mancha, Avda. Carlos III, s/n, 45071, Toledo, Spain.
Valentín E
VE
Fernández-Elías
Juan F
JF
Ortega
Rachael K
RK
Nelson
Ricardo
R
Mora-Rodriguez
D001642:Bicycling / Q000502:physiology*; D001834:Body Water / Q000378:metabolism*; D006003:Glycogen / Q000378:metabolism*; D018869:Heat-Shock Response / Q000502:physiology*; D006358:Hot Temperature; D006801:Humans; D008297:Male; D018482:Muscle, Skeletal / Q000502:physiology*; D010807:Physical Endurance / Q000502:physiology*; D020127:Recovery of Function / Q000502:physiology; D055815:Young Adult
D006003:Glycogen