The effect of double--blind carbohydrate ingestion during 60 km of self-paced exercise in warm ambient conditions.

This study evaluated double blind ingestions of placebo (PLA) versus 6% carbohydrate (CHO) either as capsules (c) or beverage (b) during 60 km self-paced cycling in the heat (32°C and 50% relative humidity). Ten well-trained males (mean ± SD: 26±3 years; 64.5±7.7 kg and 70.7±8.8 ml.kg-1.min-1 maximal oxygen consumption) completed four separate 60 km time trials (TT) punctuated by 1 km sprints (14, 29, 44, 59 km) whilst ingesting either PLAb or PLAc or CHOb or CHOc. The TT was not different among treatments (PLAb 130.2±11.2 min, CHOb 140.5±18.1 min, PLAc 143.1±29.2 min, CHOc 137.3±20.1 min; P>0.05). Effect size (Cohen's d) for time was only moderate when comparing CHOb - PLAb (d = 0.68) and PLAb - PLAc (d = 0.57) whereas all other ES were 'trivial' to 'small'. Mean speed throughout the trial was significantly higher for PLAb only (P<0.05). Power output was only different (P<0.05) between the sprints and low intensity efforts within and across conditions. Core and mean skin temperatures were similar among trials. We conclude that CHO ingestion is of little or no benefit as a beverage compared with placebo during 60 km TT in the heat.

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 (PLA(c)) effect can make the ergogenic qualities of substances more difficult to determine. Therefore, this study tested the effect of double blind ingestion of PLA(c) and CHO(c) in capsules versus known capsule (CHO(k)) 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(-1) min(-1) peak 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 CHO(c) and CHO(k) was similar but higher (p<0.05) than PLA(c) from 45 min to end of exercise. There were no differences in TTE between PLA(c) (125.2+/-37.1 min) or CHO(c) (138.8+/-47.0 min) or between CHO(c) and CHO(k) (155.8+/-54.2 min). Time to volitional exhaustion was different between PLA(c) and CHO(k) (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.