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

ABSTRACT 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.