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.