Kjertakov, Metodija (2024) Thermoregulatory and physiological responses to post-exercise hot water immersion and effects on endurance cycling performance. PhD thesis, Victoria University.

Abstract

In 2016, repeated post-exercise head-out 40°C water immersion emerged as a practical heat acclimation strategy that improves endurance exercise performance in the heat in physically active individuals. However, it remains to be determined whether this heat acclimation strategy could improve endurance performance in the heat in well-trained endurance athletes. It would also be of interest to examine inflammatory and oxidative stress responses to this heat acclimation strategy. Addressing that question is relevant, given that the degree of hyperthermia associated with postexercise 40°C water immersion induces inflammation and oxidative stress, and knowing that both physiological events can impact exercise performance. Another concern related to the post-exercise 40°C water immersion intervention is the risk of heat illness. Therefore, it is important to identify a thermometric method that would be suitable for monitoring body core temperature during hot water immersion sessions in ‘real life’. Study One examined the effects of repeated post-exercise head-out hot (40°C) water immersion on physiological and exercise performance outcomes in warm and hot environmental conditions in a group of well-trained non-heat acclimated male endurance athletes. Methods: Sixteen well-trained male cyclists completed a six-day intervention involving a daily cycling exercise for 40 minutes at 50% of their peak power output in a cool environment (14°C, 40% RH) followed immediately by either hot water immersion (HWI; n = 8) or thermoneutral water immersion (CON; n = 8) for 40 minutes. At baseline and post-intervention, participants completed two 30-minute continuous cycling tests followed by 20-km time trial tests (one at 27°C, 40% RH and the other one at 35°C, 40% RH) on two different days separated by one day of rest. Results: The HWI group showed a significantly decreased peak heart rate (-7.37 ± 5.21 beats∙min-1, p = 0.03), peak thermal sensation (-0.56 ± 0.41 arbitrary units, p < 0.01), and rating of perceived exertion (-1.00 ± 0.75 arbitrary units, p = 0.02) during the 30-minute continuous test at 27°C. The HWI group also showed a significantly decreased peak thermal sensation (-0.50 ± 0.53 arbitrary units, p = 0.03) and peak rating of perceived exertion (-1.62 ± 1.06 arbitrary units, p = 0.01) during the 30-minute continuous test at 35°C. None of these variables were altered in the CON group. Furthermore, the HWI group showed only a tendency for improved 20 km time trial performance at 27°C (p = 0.06) and 35°C (p = 0.06). Conclusion: The findings from this study indicate that a six-day post-exercise hot water immersion reduces cardiovascular and perceptual strain during exercise at 27°C and reduces only perceptual strain during moderate-intensity exercise at 35°C. Although the postexercise hot water immersion intervention did not significantly improve the 20 km time trial performance either at 27°C or 35°C, the reduction in the completion time of the latter test by 1.77% in the HWI group can be considered practically significant. Study Two determined the acute and chronic effects of exposure to post-exercise head-out immersion in 40°C water on plasma cytokine response, oxidative stress, and antioxidant capacity. Methods: Fourteen well-trained male cyclists completed a sixday intervention involving a daily cycling exercise for 40 minutes at 50% of their peak power output in a cool environment (14°C, 40% RH) followed immediately by either hot water immersion (HWI; n = 7) or thermoneutral water immersion (CON; n = 7) for 40 minutes. Ten ml of a venous blood sample was taken before and after the first session to assess acute inflammatory responses, oxidative stress, and total antioxidant capacity. Resting venous blood was also sampled 48 hours after the last session to assess chronic inflammatory responses, oxidative stress, and total antioxidant capacity. The inflammatory response was assessed by measuring the following cytokines: tumour necrosis factor (TNF)-α, interleukin (IL)-1β, IL-1 receptor antagonist (IL-1ra), IL-6, and IL-10. Oxidative stress was determined by measuring thiobarbituric acid-reactive substances (TBARS), whereas total antioxidant capacity (TAC) was measured as a sum of all antioxidants in the plasma. Results: Acute postexercise hot water immersion had no significant effects on any of the measured biomarkers (all p > 0.05). Acute post-exercise immersion in 34°C water significantly increased IL-6 (p < 0.01). Post-exercise hot water immersion over six consecutive days significantly increased resting plasma IL-1β concentration (p < 0.01). Conclusion: This study suggests that chronic heat stress imposed by post-exercise hot water immersion induces an inflammatory response but not oxidative stress in welltrained male endurance athletes. Study Three examined whether commercially available tympanic thermometers could be a suitable substitute for the expensive ingestible telemetric pills or invasive rectal probes for monitoring core temperature during the post-exercise head-out 40°C water immersion. Methods: Sixteen male cyclists cycled for 40 minutes at 50% of their peak power output in a cool environment (14°C, 40% RH), after which they were immersed in a bath of hot water for 40 minutes. Participants' tympanic and core temperatures were measured at rest, after exercise, and every 10 minutes throughout the hot water immersion session. The tympanic temperature was measured by GeniusTM 2 and Braun Pro 4000 Thermoscan tympanic thermometers, whereas core temperature was measured via an ingestible telemetric pill. The latter was used as a reference against which the tympanic thermometers were validated. Results: No statistically significant differences in temperature readings were observed between the telemetric pill and Braun Pro 4000 Thermoscan at any time point during the hot water immersion session, and these temperature readings were significantly correlated at all time points. The overall bias in temperature reading provided by Braun Pro 4000 Thermoscan relative to the telemetric pill was within the acceptable limit (< 0.3°C). Temperatures provided by GeniusTM2 at the 20-, 30, and 40-minute time points during the hot water immersion period were significantly higher than those of the telemetric pill, and there were no correlations between the devices at the last two time points. The overall mean bias associated with the GeniusTM2 tympanic thermometer was 0.50°C. Conclusion: The findings from this study indicate that Braun Pro 4000 Thermoscan could be a suitable tool for monitoring core temperature during post-exercise head-out 40°C water immersion. Unfortunately, GeniusTM2 did not pass the validity testing and thus it is not recommended for use during hot water immersion.

Search Google Scholar

Repository staff login