The effect of placebo on endurance capacity in normal weight children - A randomized trial

Background: The aim of the study was to examine the influence of the placebo effect on the endurance capacity 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 percentage), a progressive treadmill exercise test to evaluate endurance capacity, and filled habitual activity questionnaire. The participants were examined twice, in a 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 bpm), higher stage achieved and longer time of exercise to exhaustion (700.1 ± 155.2 vs. 893.3 ± 150.1 s). 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 (18.3 ± 1.4 vs 16.2 ± 1.5). Although the 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 endurance capacity 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. Trial registration: ClinicalTrial.gov identifier: NCT03165604, Registered May 24, 2017.