Effect of hot water immersion at different temperatures during a transition period on vertical jump performance

Increased muscle temperature (Tm) enhances exercise performance but can decrease during the transition period between warm-up and competition. Although passive warming strategies can maintain Tm, the optimal heating temperatures and their effects on performance are unclear. Seventeen healthy males participated in this study with four experimental conditions: no intervention (CON), hot water immersion at 36°C (HWI36), 39°C (HWI39), and 42°C (HWI42) during a 20-min transition period. Vertical jump (VJ) performance, core temperature (Tc), heart rate (HR), and perceived thermal comfort were measured across eight VJ sets (VJ 1-8) performed over 1 h, and biomechanical analyses were conducted to understand the changes in jump performance. The improved VJ performance was primarily due to improved range of motion and concentric muscle contraction. These findings provide valuable insights for the optimization of passive warming strategies in competitive sports.