The Effect of Placebo on Aerobic Stress Test Results in Normal Weight Children

Background: Placebo have been traditionally defined as medically inert substance used primarily as controls in clinical trials. However, in recent decades, more and more studies have started focusing on the placebo effect as a psychobiological effect carrying curative potential. The aim of the study was to examine the influence of the placebo effect on physical fitness test results in normal weight children.

Methods: Twenty-four pre-pubertal normal-weight children aged 6-13 years participated in the study. Subjects underwent anthropometric measurements (weight, height, BMI percentile, and fat percentile), a progressive treadmill exercise test to evaluate fitness, and filled a habitual activity questionnaire. The participants were examined twice, in random order, with each child being compared to him/herself. Different types of information were provided regarding a water drink consumed prior to testing - standard information (water) vs. deliberate positive information (presumed energy drink, placebo).

Results: Following the placebo drink, children demonstrated significantly higher peak pulse (177.9±13.6 vs. 189.8±12.2), higher stage achieved and longer time of exercise to exhaustion (700.1±155.2 vs. 893.3±150.1). Although the exercise duration was longer, stage and heart rate achieved were higher, the reported average, and peak rate of perceived exertion (RPE) were significantly lower for the placebo [11.7 (11.3-12.6) vs 10.4 (9.7-11.0)]. Moreover, although effort was higher while drinking placebo (longer run, higher exercise phase, higher heart rate), recovery time was significantly shorter. The reported differences were not associated with order of tests, age, gender or child activity level.

Conclusion: Our results demonstrate a significant information placebo effect on children`s fitness test results. This highlights the possible role of positive information (placebo) in trying to encourage physical activity in children. Whether this effect could be applied to longer term interventions has yet to be tested.