Hot‐ and Cold‐Water Immersion Do Not Alter Performance or Perceived Fatigability but Improve Muscle Activation, Cardiac Vagal Modulation, and Cardiorespiratory Recovery After Distinct Running Protocols

This study investigated the effects of cold-water immersion (11°C, CWI_11°) and hot-water immersion (41°C, HWI_41°) on components of fatigability after distinct high-intensity endurance running protocols. Participants completed either continuous running at the velocity associated with the respiratory compensation point (vRCP; CONT_100%RCP, n = 12) or intermittent running at 50% above vRCP (HIIT_150%RCP, n = 10). Assessments were performed at baseline, immediately after, and at 2, 4, and 24 h postexercise. These included voluntary and evoked knee-extensor contractions, countermovement jumps, mood state, cardiac autonomic modulation, and cardiorespiratory and perceptual responses during submaximal brief runs. Compared to placebo and regardless of preceding running protocol, CWI_11° enhanced cardiac vagal modulation at 2 h postexercise (condition × time interaction, p < 0.05), whereas HWI_41° reduced oxygen consumption rate during submaximal brief runs within 24 h postexercise (condition effect, p < 0.05). Furthermore, compared to placebo, HWI_41° increased vastus lateralis activation during maximal voluntary contractions (RMS/M-wave_amp) 2 and 4 h after the CONT_100%RCP, while CWI_11° increased it at the same time points after the HIIT_150%RCP (condition × time interactions, p < 0.05). The efficacy of CWI_11° and HWI_41° as recovery interventions after running depended on the specific component of fatigability being assessed and the preceding exercise protocol. While CWI_11° increased cardiac vagal modulation and HWI_41° reduced oxygen consumption rate in post-intervention submaximal brief runs, neither intervention improved knee-extensor voluntary or involuntary peak force, perceptual responses, or mood disturbance. Both HWI_41° and CWI_11° enhanced muscle activation during maximal voluntary contractions; however, this benefit was observed with HWI_41° after continuous endurance running and with CWI_11° following high-intensity intermittent running.