Post-exercise Hot Water Immersion Elicits Heat Acclimation Adaptations in Endurance Trained and Recreationally Active Individuals

Abstract

Hot water immersion (HWI) after exercise on 6 consecutive days in temperate conditions has been shown to provide heat acclimation adaptations in a recreationally active population. Endurance athletes experience frequent, sustained elevations in body temperature during training and competition; as a consequence, endurance athletes are considered to be partially heat acclimatized. It is therefore important to understand the extent to which endurance trained individuals may benefit from heat acclimation by post-exercise HWI. To this end, we compared the responses of eight endurance trained and eight recreationally active males (habitual weekly endurance exercise: 9 h vs. 3 h) to a 6-day intervention involving a daily treadmill run for 40 min (65% O2max) in temperate conditions followed immediately by HWI (≤40 min, 40°C). Before (PRE) and after the intervention (POST), hallmark heat acclimation adaptations were assessed during a 40-min treadmill run at 65% O2max in the heat (33°C, 40% RH). The 6 day, post-exercise HWI intervention induced heat acclimation adaptations in both endurance trained and recreationally active individuals. Training status did not significantly influence the magnitude of heat acclimation adaptations from PRE to POST (interactions P > 0.05) for: the reduction in end-exercise rectal core temperature (Tre, mean, endurance trained -0.36°C; recreationally active -0.47°C); the reduction in resting Tre (endurance trained -0.17°C; recreationally active -0.23°C); the reduction in Tre at sweating onset (endurance trained -0.22°C; recreationally active -0.23°C); and, the reduction in mean skin temperature (endurance trained -0.67°C; recreationally active -0.75°C: PRE to POST P < 0.01). Furthermore, training status did not significantly influence the observed reductions in mean O2, mean metabolic energy expenditure, end-exercise physiological strain index, perceived exertion or thermal sensation (PRE to POST P < 0.05). Only end-exercise heart rate was influenced by training status (P < 0.01, interaction); whereby, recreationally active but not endurance trained individuals experienced a significant reduction in end-exercise heart rate from PRE to POST (P < 0.01). In summary, these findings demonstrate that post-exercise HWI presents a practical strategy to reduce thermal strain during exercise-heat-stress in endurance trained and recreationally active individuals.

Heat alleviation strategies for athletic performance: A review and practitioner guidelines

“…Further to chamber-based HA protocols, alternate, cheaper and more accessible methods are now acknowledged as methods for passive (e.g. hot water bath) [95][96][97][98] and active HA strategies (e.g. overdressing and restricting heat loss during routine training) [99][100][101].…”

“…Passive strategies include; residing in simulated heat stress in environmental chambers [16,[117][118][119], wearing restricted heat loss attire (e.g. over dressing in heat stress) [120], wearing water-perfused suits [109,121], sauna exposures [95,122] or hot water immersion (HWI) [96][97][98]112,123,124], all of which "raise and maintain" a moderately high T CORE (e.g. 38.0-38.5°C) alongside high T SKIN (>38.5°C).…”

“…A recent review of passive methods [125] concluded that these strategies can be used to induce heat adaptations, such as a reduced resting and/or exercising T CORE [96][97][98]119,121,124], T SKIN [96,98,121], and HR [96,98,118,126]. Passive methods for HA also improve sweat onset thresholds and enhance sweat capacity [98,127].…”

“…5 km time trial) [95,98]. Post-exercise HWI appears to be the most well-reported intervention to induce adaptations in thermoregulatory and performance physiology associated with HA, with the magnitude of adaptation similar irrespective of training status [97]. To implement this technique, athletes should undertake their normal training in routine environmental conditions, and then seek to immediately submerge themselves to shoulder height iñ 40°C water, with immersion times ranging from 10 to 40 min.…”

Effect of contrast water therapy on blood lactate concentration after high-intensity interval training in elite futsal players

“…Conversely, the application of HWi has been shown to increase tissue temperature, metabolite production, and muscle elasticity, to stimulate local blood flow, and to reduce muscle spasm [32]. Also, Zurawlew et al [33] imply that HWi is commonly used to reduce pain or strain and promote healing in soft tissue injuries.…”