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 degrees C, CWI11 degrees) and hot-water immersion (41 degrees C, HWI41 degrees) 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; CONT100%RCP, n = 12) or intermittent running at 50% above vRCP (HIIT150%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, CWI11 degrees enhanced cardiac vagal modulation at 2 h postexercise (condition x time interaction, p < 0.05), whereas HWI41 degrees reduced oxygen consumption rate during submaximal brief runs within 24 h postexercise (condition effect, p < 0.05). Furthermore, compared to placebo, HWI41 degrees increased vastus lateralis activation during maximal voluntary contractions (RMS/M-wave(amp)) 2 and 4 h after the CONT100%RCP, while CWI11 degrees increased it at the same time points after the HIIT150%RCP (condition x time interactions, p < 0.05). The efficacy of CWI11 degrees and HWI41 degrees as recovery interventions after running depended on the specific component of fatigability being assessed and the preceding exercise protocol. While CWI11 degrees increased cardiac vagal modulation and HWI41 degrees 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 HWI41 degrees and CWI11 degrees enhanced muscle activation during maximal voluntary contractions; however, this benefit was observed with HWI41 degrees after continuous endurance running and with CWI11 degrees following high-intensity intermittent running.