Rationale:
Previous studies have shown that many subjective and objective outcomes can be affected by a placebo. Although control groups are normally included in exercise studies there are few studies documenting the placebo effect in exercise performance.
Objectives:
This study was designed to measure objective and subjective markers of the placebo effect on exercise performance.
Methods:
Thirty-two experienced runners, ranging from recreational to competitive, completed an exercise test to measure fitness level (VO2 max = 60.8 +/- 8.2 ml*kg-1). Each subject subsequently ran three 5-km time trials on an indoor track. The first run was for habituation. In the last two trials, subjects were randomly assigned to drink either 475 ml of bottled water which was correctly identified as water (CONTROL) or to drink water that they were told was superoxygenated water (PLACEBO) 20 minutes prior to their run. Before the trials they had watched a video designed to convince them that the PLACEBO was ergogenic. Total time, heart rate (HR), post exercise rating of perceived exertion (RPE), and blood lactate were measured.
Results:
There was a significant difference (P < .05) between (CONTROL vs PLACEBO) for total time (21:04 +/- 3:34 vs 19:41 +/- 2:32). HR during the trials did not differ at any point during the run, nor did post-exercise RPE (7.7 +/- 1.4 vs 7.7 +/- 1.2) or lactate (9.8 +/- 3.9 vs 10.2 +/- 3.7 mmol*l-1). The improved performance with placebo was largely attributable to improved performance in the less accomplished runners (time >20 min; 2:22 faster) versus the more accomplished runners (time <20 min; 0:28 faster)
Conclusion:
The study demonstrates that a placebo effect alters exercise performance and must be accounted for by appropriate control procedures.