Fat-free mass mediates the association between body mass and jump height in healthy young adults.

Background: The countermovement jump (CMJ) is a reliable and valid test of lower-extremity (LE) muscle power and neuromuscular performance. Body mass is positively associated with CMJ performance in young adults, warranting the examination of the influence of body composition on jump height (JH). This study examined the mediation effects of body composition on CMJ performance in young adults. The hypothesis was that fat-free mass and percent fat mass would significantly mediate the association between body mass with JH in young adults.

Methods: Healthy young adults (N.=81; 47 female; mean age 25.1±3.4) completed this study and underwent body composition assessment using a bioelectrical impedance analysis device. Participants performed three CMJ trials to measure average JH using an electronic jump mat. Mediation analysis models were performed to examine the hypothesis of this study.

Results: The mediation analyses indicated that the indirect effects of fat-free mass on the association between body mass with JH were significant (indirect effect [IE]=-0.23, 95% CI -0.315, 0.767; IE=0.76, 95% CI 0.334, 1.272; respectively), after controlling for sex and percent fat mass.

Conclusions: The association between body mass with JH in young adults with normal BMI was mediated by fat-free mass. Clinicians, trainers, and coaches should potentially target increasing fat-free mass when improving LE power and neuromuscular performance in rehabilitation and sports settings in this population, but further studies are needed.