Clark, V. R., Hopkins, W. G., Hawley, J. A., & Burke, L. M. (2000). Placebo effect of carbohydrate feedings during a 40-km cycling time trial. Medicine and Science in Sports and Exercise, 32, 1642-1647.

The placebo effect is a favorable performance outcome derived from the belief that a beneficial treatment has been received. This effect was investigated for carbohydrate supplements during a high-intensity endurance performance lasting one hour.

Competitive endurance cyclists (F = 2; M = 41) performed two simulated 40-km time trials on an air-braked ergometer. The first trial with water ingestion, established a baseline. In the second trial 6-8 days later, Ss were divided into a carbohydrate ingestion group, and a noncaloric placebo group. Ss in each group were further subdivided into three subgroups according to whether they were told the drink contained CHO or placebo, or not told at all.

The placebo effect of CHO was ~4% enhancement of mean power, roughly equivalent to a 1.5% increase in speed. There was a negligible real effect of CHO supplementation on the high-intensity endurance test lasting one hour.

Implication. In a one-hour endurance event, CHO supplementation is likely to have a placebo, rather than a true effect.

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