Effects of Heat Acclimation and Acclimatisation on Maximal Aerobic Capacity Compared to Exercise Alone in Both Thermoneutral and Hot Environments: A Meta‑Analysis
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Link: https://rdcu.be/cjaZe 

I read this paper with great interest.
The paper focuses on several questions. However, this short thread will focus on one—the effect of heat acclimation on maximal capacity in thermoneutral conditions.
The paper concludes that there was a higher (small) improvement in VO2max performance in a HA compared to control, with a std. mean difference of 0.30, 95% CI = 0.06 to 0.54.

I am of the opinion that this result is inaccurate, and I explain why below.
A fixed-effects-model was chosen for the original analysis. This assumes that ‘all studies along with their effect sizes stem from a single homogeneous population’.
However, the studies included men and women, and participants with a variety of sport backgrounds, including table tennis and cycling, in addition to military personnel. In this context, a random-effect model is likely more appropriate. https://bookdown.org/MathiasHarrer/Doing_Meta_Analysis_in_R/random.html
There are also instances of double counting, studies: Gore (1997), Willmott (2018) and Schvartz (1977).

https://handbook-5-1.cochrane.org/chapter_16/16_5_4_how_to_include_multiple_groups_from_one_study.htm
After selecting a random-effects-model and correcting for double counting of studies, the substantive conclusion changes—there is no evidence that HA has an effect on VO2max performance (in thermoneutral conditions), with a SMD of 0.06, 95% CI = -0.56 to 0.44.
I considered more closely the study by Schvartz (1977), where three groups (n=7 each group) of men with different VO2max capacities were recruited.
This study had a relatively strong influence on the effect size, but not the substantive conclusion of my analysis. However, ‘no effect’ is now perhaps less convincing, as the SMD without this study was -0.24, 95% CI = -0.63 to 0.15.
🚹Disclaimer: I spent only a small amount of time on this and there could be errors (possibly with the pooled SD), if there are please let me know.
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