Electrolyte supplementation during severe energy restriction increases exercise capacity in the heat.
OBJECTIVE
This study examined the effects of sodium chloride and potassium chloride supplementation during 48-h severe energy restriction on exercise capacity in the heat.


METHODS
Nine males completed three 48-h trials: adequate energy intake (100 % requirement), adequate electrolyte intake (CON); restricted energy intake (33 % requirement), adequate electrolyte intake (ER-E); and restricted energy intake (33 % requirement), restricted electrolyte intake (ER-P). At 48 h, cycling exercise capacity at 60 % VO2 peak was determined in the heat (35.2 °C; 61.5 % relative humidity).


RESULTS
Body mass loss during the 48 h was greater during ER-P [2.16 (0.36) kg] than ER-E [1.43 (0.47) kg; P < 0.01] and CON [0.39 (0.68) kg; P < 0.001], as well as greater during ER-E than CON (P < 0.01). Plasma volume decreased during ER-P (P < 0.001), but not ER-E or CON. Exercise capacity was greater during CON [73.6 (13.5) min] and ER-E [67.0 (17.2) min] than ER-P [56.5 (13.1) min; P < 0.01], but was not different between CON and ER-E (P = 0.237). Heart rate during exercise was lower during CON and ER-E than ER-P (P < 0.05).


CONCLUSIONS
These results demonstrate that supplementation of sodium chloride and potassium chloride during energy restriction attenuated the reduction in exercise capacity that occurred with energy restriction alone. Supplementation maintained plasma volume at pre-trial levels and consequently prevented the increased heart rate observed with energy restriction alone. These results suggest that water and electrolyte imbalances associated with dietary energy and electrolyte restriction might contribute to reduced exercise capacity in the heat.
School of Sport, Exercise and Health Sciences, Loughborough University, Loughborough, UK. L.James@Lboro.ac.uk.
Lewis J
LJ
James
School of Sport, Exercise and Health Sciences, Loughborough University, Loughborough, UK.
Stephen A
SA
Mears
School of Sport, Exercise and Health Sciences, Loughborough University, Loughborough, UK.
Susan M
SM
Shirreffs
D000328:Adult; D031204:Caloric Restriction; D017079:Exercise Tolerance / Q000187:drug effects*; D006358:Hot Temperature; D006801:Humans; D008297:Male; D017419:Potassium, Dietary / Q000494:pharmacology*; D012982:Sodium, Dietary / Q000494:pharmacology*; D014882:Water-Electrolyte Balance
D017419:Potassium, Dietary; D012982:Sodium, Dietary
Dehydration; Fasting; Fluid balance; Hydration; Hypohydration