The Effect of a Single Session of Postexercise Hot Water Immersion on Same Day Aerobic Performance and Recovery Status.

ABSTRACT Wheelock, CE, Lavoie, EM, Pryor, JL, Pryor, RR, Colburn, D, Johnson, BD, and Hostler, D. The effect of a single session of postexercise hot water immersion on same day aerobic performance and recovery status. J Strength Cond Res XX(X): 000-000, 2025-Postexercise hot water immersion (HWI) passively induces high thermal loads, but its acute effect on subsequent exercise is unknown. The purpose of this study was to evaluate aerobic performance and recovery status after a single HWI session. Twelve subjects (6 males; V̇o2peak: 44.9 ± 5.9 ml·kg-1·min-1) completed 3 randomized trials. Two trials were exercise with 30 minutes of HWI (39°C) followed by an identical exercise session 8 h (HWI-8; n = 12) or 24 h (HWI-24; n = 12) later. In the control (CON; n = 12), subjects rested after exercise and completed the second exercise session 8 h later. Movement economy (ME) was measured on a treadmill at 3 stages (6.0, 8.0, and 10.0 km·h-1) followed by a 15-minute running time trial (TT) for maximum distance. Plasma volume change (ΔPV) from baseline was calculated. Perceived recovery was measured before the second exercise session. Independent effects of HWI (HWI-8 vs. CON) and HWI recovery time (HWI-8 vs. HWI-24) were assessed. Significance was accepted at p ≤ 0.05. As expected, HWI induced a greater thermal load after exercise compared with CON (p < 0.001). Hot water immersion induced greater body mass loss and sweat rates, but did not affect ΔPV compared with CON. After 8 h of recovery, ME and TT distance during HWI-8 (2.4 ± 0.4 km) was similar to CON (2.5 ± 0.4 km; p = 0.10), though TT declined by 3.8 ± 5.8% after HWI during same day exercise. Hot water immersion-24 TT (2.6 ± 0.5 km; p < 0.01) and subjective recovery (p < 0.01) were greater than HWI-8, while ME was not different. This study saw no effect of a single 30-minute HWI on ME, TT performance, or ΔPV compared with control. Increased running performance and perceived recovery status were observed 24 h compared with 8 h after HWI.