Double blind carbohydrate ingestion does not improve exercise duration in warm humid conditions

The positive effects of carbohydrate (CHO) supplementation on endurance exercise are well documented but the placebo (PLAc) effect can make the ergogenic qualities of substances more difficult to determine. Therefore, this study tested the effect of double blind ingestion of PLAcand CHOcin capsules versus known capsule (CHOk) ingestion on prolonged exercise heat stress. Nine well trained male volunteers (mean ± S.D.: 23 ± 3 years; 62.4 ± 6.5 kg and 65.8 ± 5.2 mL kg-1min-1peak oxygen consumption) exercised at 60% of maximum power output until volitional exhaustion (TTE) in the three different conditions. Capsules were ingested with 252 ± 39 mL of water. Blood glucose in CHOcand CHOkwas similar but higher (p <0.05) than PLAcfrom 45 min to end of exercise. There were no differences in TTE between PLAc(125.2 ± 37.1 min) or CHOc(138.8 ± 47.0 min) or between CHOcand CHOk(155.8 ± 54.2 min). Time to volitional exhaustion was different between PLAcand CHOk(p <0.05). Increased TTE resulted when participants and researchers knew the capsule content, but not in the double blind condition. The difference could be related to a combined effect of CHO ingestion and knowledge of what was ingested possibly acting as a potent psychological motivator. © 2007 Sports Medicine Australia.