Want to be fit? Start with your mind! The role of the placebo effect in physical fitness in children: a preliminary systematic review and meta-analysis

Physical activity is crucial to prevent and reduce excess body mass. The placebo effect can influence the outcomes of fitness-related interventions; however, this topic has not yet been extensively investigated in children. Summarising the data on placebo effects in fitness-related interventions is essential to understand this problem better. A systematic review of PubMed, Cochrane, PsycINFO, PsycARTICLES, TripDatabase and Embase was carried out. A meta-analysis of the results of studies with comparable research plans was performed. There were significant differences, favouring the placebo intervention. At the final follow-up, the children in placebo groups had higher maximal heart rates, shorter recovery times, longer ergometry phases, running time and lower peak and average perceived exertion than the control. The placebo effect is present in fitness-related parameters in children, regardless of the Body Mass Index status. It is crucial, as for youth with excess body mass, it is difficult to be active, especially to show appropriate levels of motivation and involvement. Importantly, the benefits of the placebo were the strongest in the motivation/ engagement-related parameters and self-assessed exertion. Notably, the nocebo effect was not observed, which is advantageous when considering placebo interventions in practice.