The effects of creatine (Cr) supplementation on cardiovascular, metabolic, and thermoregulatory responses, and on the capacity of trained humans to perform prolonged exercise in the heat was examined. Endurance-trained males (n = 21) performed 2 constant-load exercise tests to exhaustion at 63 ± 5 % VO2max in the heat (ambient temperature: 30.3 ± 0.5 °C) before and after 7 d of Cr (20 g · d–1 ’ Cr + 140 g • d–1 glucose polymer) or placebo. Cr increased intraccl-lular water and reduced thermoregulatory and cardiovascular responses (e.g., heart rate, rectal temperature, sweat rate) but did not significantly increase time to exhaustion (47.0 ± 4.7 min vs. 49.7 ± 7.5 min, P = 0.095). Time to exhaustion was increased significantly in subjects whose estimated intramuscular Cr levels were substantially increased (“responders”: 47.3 ± 4.9 min vs. 51.7 ± 7.4 min, P = 0.031). Cr-induced hyperhydration can result in a more efficient thermoregulatory response during prolonged exercise in the heat.
L.P. Kilduff, E. Gcorgiades, R.H. Minnion, M. Mitchell, M. Hadjicharlambous. and Y.P. Pitsiladis are wilh the Centre for Exercise Science and Medicine in the Institute of Biomedical and Life Sciences at the University of Glasgow. Glasgow, GI2 XQQ, UK. Kilduff and N. James arc with the Dept of Sports Science at the University of Wales, Swansea, SA2 8PP, UK. D. Kingsmore is with the University Dept of Surgery. Western Infirmary, Glasgow, G11 6NT, UK.