The time course of adaptations in thermoneutral maximal oxygen consumption following heat acclimation

Abstract

Purpose This study investigated the effects of a 10-day heat acclimation (HA) programme on the time course of changes in thermoneutral maximal oxygen uptake ($$\dot{V}$$ V ˙ O2max) during and up to 10 days post-HA. Methods Twenty-two male cyclists were assigned to a HA or control (Con) training group following baseline ramp tests of thermoneutral $$\dot{V}$$ V ˙ O2max. Ten days of fixed-intensity (50% baseline $$\dot{V}$$ V ˙ O2max) indoor cycling was performed in either ~ 38.0 °C (HA) or ~ 20 °C (Con). $$\dot{V}$$ V ˙ O2max was re-tested on HA days 5, 10 and post-HA days 1, 2, 3, 4, 5 and 10. Results $$\dot{V}$$ V ˙ O2max initially declined across time in both groups during training (P < 0.05), before increasing in the post-HA period in both groups (P < 0.05). However, $$\dot{V}$$ V ˙ O2max was higher than control by post-HA day 4 in the HA group (P = 0.046). Conclusions The non-linear time course of $$\dot{V}$$ V ˙ O2max adaptation suggests that post-testing should be performed 96-h post-training to identify the maximal change for most individuals. In preparation for training or testing, athletes can augment their aerobic power in thermoneutral environments by performing 10 days HA, but the full effects will manifest at varying stages of the post-HA period.

Heat acclimation during low‐intensity exercise increases and Hsp72, but not markers of mitochondrial biogenesis and oxidative phosphorylation, in skeletal tissue

“…Our data agree with a recently published meta-analysis with 23 studies which reported a small but significant effect of HA onV O 2 max (Hedge's g = 0.30) measured in a temperate environment (Benjamin et al, 2019 or approximately 5%) in a temperate environment using trained cyclists . Recently, Waldron et al (2019) Figure 1). We propose that these results may be due to a higher absolute intensity (walking/running speed) and heat accumulation experienced by our participants with greater baselineV O 2 max .…”

“…Recently, Waldron et al. (2019) investigated the time course changes in in temperate environment during and up to 10 days post‐HA and showed that was significantly different only at 4 days post‐HA (or 96 h after the last session). In short, it is still unclear if HA independently improves aerobic fitness in temperate environments, and outcomes are likely dictated by the HA protocol, time course changes and population studied.…”

“…A low exercise intensity (<50%V O 2 max ) was selected as it would induce heat acclimation while minimizing the exercise training-induced molecular signals (PGC-1α and cytochrome c oxidase subunit 4 (COX-4)) to mitochondrial biogenesis (Di Donato et al, 2014;Gaesser & Rich, 1984). A control group was not used in the present study as it has been shown previously that 10 days of exercise training at an intensity similar to the present study (50%V O 2 max ) in a temperate environment does not increaseV O 2 max (Waldron, Jeffries, Tallent, Patterson, & Nevola, 2019).…”

Performance Changes Following Heat Acclimation and the Factors That Influence These Changes: Meta-Analysis and Meta-Regression

“…Another meta-analysis has extensively examined the timeline of HA decay and concluded that internal body temperature and heart rate responses typically decay at a rate of 2.5% per day (Daanen et al, 2018). The importance of recovery has even been examined and reported when seeking optimal training improvements in a thermoneutral environment and 96 h of rest following training was suggested (Waldron et al, 2019). The results from both of these manuscripts point to the importance of finding the appropriate balance between recovery and acclimation decay for optimal performance results.…”

Effectiveness of Short-Term Heat Acclimation on Intermittent Sprint Performance With Moderately Trained Females Controlling for Menstrual Cycle Phase

“…Prior to acclimation, as a control trial, two HST’s (HST1 vs. HST2) were performed and separated by 1 week. The post acclimation HST3 was performed within a week (5 ± 2 days) of the final acclimation day to prevent the decay of acclimation (Garrett et al, 2009) and we acknowledge there may be some variability in the magnitude of response (Waldron et al, 2019). To control for menstrual cycle phase the HST2 (Pre-) and HST3 (Post-) STHA trials were performed in week three of the menstrual cycle (luteal phase), in the active pill portion of the OCP for all participants.…”