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The effects of substrate and fluid provision on thermoregulatory, cardiorespiratory and metabolic responses to prolonged exercise in a cold environment in man
Author(s) -
Galloway SD,
Maughan RJ
Publication year - 1998
Publication title -
experimental physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.925
H-Index - 101
eISSN - 1469-445X
pISSN - 0958-0670
DOI - 10.1113/expphysiol.1998.sp004125
Subject(s) - respiratory exchange ratio , heart rate , hyperventilation , glycogen , chemistry , cardiorespiratory fitness , zoology , vo2 max , expired air , medicine , physical exercise , thermoregulation , respiratory rate , fluid intake , exertion , endocrinology , blood pressure , biology
During prolonged exercise in a cold environment, fatigue is generally associated with a depletion of endogenous glycogen stores. This has lead many authors to hypothesize that the carbohydrate (CHO) content of fluids ingested in cool environments should be high, yet this hypothesis has not been specifically examined. In the present study, six healthy males cycled to exhaustion at approximately 80% of their maximum oxygen consumption (V2O,max) with either no drink (ND), a 15% CHO‐electrolyte drink (15% CHO) or a 2% CHO electrolyte drink (2% CHO). Dietary intake and exercise were replicated 2 days prior to each trial. Mean (S.D.) ambient temperature was 10.0 (0.3) degrees C with a relative humidity of 72 (2) % and an air velocity of approximately 0.7 m s(−1) on all trials. Weighted mean skin temperature was calculated, and rectal temperature and heart rate were recorded at rest, during exercise and at exhaustion. Venous samples were drawn before and during exercise and at exhaustion for determination of haemoglobin, haematocrit, blood metabolites and serum electrolytes and osmolality. Expired air was collected for calculation of VO2 and respiratory exchange ratio which were used to estimate rates of fuel oxidation. Ratings of perceived exertion (RPE) were also obtained. Exercise capacity was not different (P=0.49) between trials, with median (range) times to exhaustion of 90.6 (66.8−106.0), 97.7 (60.9−112.0) and 102.0 (77.1−170.7) min for the ND, 15% CHO and 2% CHO trials, respectively. The 15% CHO drink significantly (P < 0.05) elevated blood glucose concentration and total CHO oxidation compared with the ND trial. The 2% CHO drink significantly (P < 0.05) reduced the estimated change in plasma volume and resulted in a lower serum osmolality than the other two trials. No differences were observed in any thermoregulatory or cardiorespiratory responses between trials. These data suggest that maintenance of blood‐borne substrate and/or plasma volume does not influence exercise capacity in the cold, as is commonly reported during this type and intensity of exercise in warmer environments.