The effects of acute hot-water immersion on force steadiness and motor unit discharge rate variability in young, healthy adults.

This study examined the effects of core and muscle temperature on force steadiness and motor unit discharge rate (MUDR) variability after a hot-water immersion session. Fifteen participants (6 women; 25 ± 6 years) completed neuromuscular assessments before and after either 42 °C (hot) or 36 °C (control) water immersion. Force steadiness was measured during knee extension, while HD-sEMG signals were recorded from vastus lateralis and medialis for MUDR variability analysis. Following water immersion, force steadiness decreased by 0.11% (p < 0.05; d = 0.38) and MUDR variability increased by 1.25% (p < 0.01; d = 0.57) potentially driven by increased muscle temperature. Elevated core temperature did not further affected these changes.