The effect of post-exercise heat exposure (passive heat acclimation) on endurance exercise performance: a systematic review and meta-analysis

Solomon, Thomas P. J.; Laye, Matthew J.

doi:10.1186/s13102-024-01038-6

BMC Sports Science, Medicine and Rehabilitation

Table 3 GRADE summary of findings

From: The effect of post-exercise heat exposure (passive heat acclimation) on endurance exercise performance: a systematic review and meta-analysis

Population: Healthy male or female adults ≥ 18 years of age of any race or ethnicity, in any research setting
Interventions: Exercise followed by post-exercise heat exposure (sauna or hot water immersion) on at least 2 consecutive days
Comparisons: The control group must complete the same exercise intervention but without post-exercise heat exposure
Outcomes	Effect of treatment (ratio of mean, or standardised mean difference)	Number of participants and studies in meta-analysis	Optimal Information Size criterion (OIS)	Quality of the evidence (certainty in the effect estimate)
Endurance performance in hot conditions (primary outcome)	ROM (95% CI) = 1.04 (0.94, 1.15) A ratio > 1 means treatment is better than control	Participants = 60 Studies = 4	OIS = 298	⊝ ⊕ ⊝ ⊝ ⊝ VERY LOW due to Risk of bias^a, Indirectness^j, Imprecision^l, and Publication bias¹³
Endurance performance in thermoneutral conditions	ROM (95% CI) = 1.06 (0.99, 1.12) A ratio > 1 means treatment is better than control	Participants = 144 Studies = 6	OIS = 664	⊝ ⊕ ⊝ ⊝ ⊝ VERY LOW due to Risk of bias^b, Indirectness^j, and Imprecision^l
V̇O₂max	SMD (95% CI) = 0.33 (0.19, 0.47) A positive value means treatment is better than control	Participants = 91 Studies = 3	OIS = 144	⊝ ⊕ ⊝ ⊝ ⊝ VERY LOW due to Risk of bias^c, Indirectness^k, Imprecision^l, and Publication bias^m
Speed at lactate threshold	SMD (95% CI) = 0.19 (-0.53, 0.92) A positive value means treatment is better than control	Participants = 55 Studies = 3	OIS = 393	⊝ ⊕ ⊝ ⊝ ⊝ VERY LOW due to Risk of bias^d, Indirectness^k, Imprecision^l, and Publication bias^m
Heart rate	SMD (95% CI) = -0.32 (-0.45, -0.20) A negative value means treatment is better than control	Participants = 163 Studies = 6	OIS = 173	⊝ ⊕ ⊝ ⊕ ⊝ VERY LOW due to Risk of bias^e, and Indirectness^k, and Imprecision^l
RPE	SMD (95% CI) = 0.11 (-0.38, 0.61) A negative value means treatment is better than control	Participants = 163 Studies = 6	OIS = 641	⊝ ⊕ ⊝ ⊝ ⊕ VERY LOW due to Risk of bias^f, Indirectness^k, and Imprecision^l
Core temperature	SMD (95% CI) = -0.44 (-0.79, -0.09) A negative value means treatment is better than control	Participants = 163 Studies = 6	OIS = 34	⊝ ⊕ ⊝ ⊕ ⊕ LOW due to Risk of bias^g and Indirectness^k
Sweat rate	SMD (95% CI) = 0.27 (0.06, 0.47) A positive value means treatment is better than control	Participants = 139 Studies = 6	OIS = 159	⊝ ⊕ ⊝ ⊝ ⊕ VERY LOW due to Risk of bias^h, Indirectness^k, and Imprecision^l
Thermal sensation	SMD (95% CI) = -0.61 (-0.98, -0.24) A negative value means treatment is better than control	Participants = 112 Studies = 5	OIS = 45	⊝ ⊕ ⊝ ⊕ ⊕ LOW due to Risk of biasⁱ and Indirectness^k
Thermal comfort	SMD (95% CI) = -0.56 (-9.78, 8.65) A positive value means treatment is better than control	Participants = 55 Studies = 2	OIS = 43	⊝ ⊕ ⊝ ⊝ ⊕ VERY LOW due to Risk of biasⁱ, Indirectness^j, and Imprecision^l

ROM = Ratio of mean between the effect of treatment and the effect of no treatment (control), interpreted as: trivial (ROM < 1.08), small (1.08 ≤ ROM < 1.22), moderate (1.22 ≤ ROM < 1.37), or large effects (ROM ≥ 1.37) of treatment. SE = standard error of ratio of mean. SMD = standardised mean difference (Hedges’ g) between the effect of treatment and the effect of no treatment (control), interpreted as: trivial (g < 0.2), small (0.2 ≤ g < 0.5), moderate (0.5 ≤ g < 0.8), or large effects (g ≥ 0.8) of treatment. CI = confidence interval
GRADE Working Group grades of evidence:
⊕ = no downgrade in the certainty in the effect estimate. ⊝ = downgrade certainty in the effect estimate
High = very confident that the true effect lies close to the effect estimate. Moderate = moderately confident in the effect estimate; the true effect is likely to be close to the effect estimate but there is a possibility that it is substantially different. Low = low confidence in the effect estimate; the true effect may be substantially different. Very Low = very little confidence in the effect estimate; the true effect is likely to be substantially different
Specific reasons for downgrading the quality of evidence:
^aRisk of bias for performance in hot conditions: 1/4 studies had a high risk of bias due to missing outcome data, 1/4 studies had a high risk of bias due to measurement of the outcome; 1/4 studies had a high risk of bias due to the selection of the reported result
^bRisk of bias for performance in thermoneutral conditions: 1/6 studies had a high risk of bias due to the randomization process; 1/6 studies had a high risk of bias due to the deviations from intended interventions; 1/6 studies had a high risk of bias due to the missing outcome data; 2/6 studies had a high risk of bias due to the measurement of the outcome; 1/6 studies had a high risk of bias due to the selection of the reported result
^cRisk of bias for V̇O₂max: 1/3 studies had a high risk of bias in all bias domains
^dRisk of bias for speed at lactate threshold: 1/2 studies had a high risk of bias in all bias domains
^eRisk of bias for heart rate: 1/6 studies had a high risk of bias due to the randomization process, deviations from intended interventions, and missing outcome data; 2/6 studies had a high risk of bias due to the measurement of the outcome; 3/6 studies had a high risk of bias due to the selection of the reported result
^fRisk of bias for RPE: 1/6 studies had a high risk of bias due to the randomization process; 2/6 studies had a high risk of bias due to deviations from intended interventions and the selection of the reported result
^gRisk of bias for core temperature: 1/6 studies had a high risk of bias due to the randomization process and deviations from intended interventions; 3/6 studies had a high risk of bias due to the selection of the reported result
^hRisk of bias for sweat rate: 1/6 studies had a high risk of bias due to the randomization process, deviations from intended interventions, and the measurement of the outcome; 4/6 studies had a high risk of bias due to the selection of the reported result
ⁱRisk of bias for thermal sensation and thermal comfort: 1/5 studies had a high risk of bias due to the randomization process and deviations from intended interventions; 2/5 studies had a high risk of bias due to the measurement of the outcome and the selection of the reported result
^jIndirectness due to substantial differences in interventions and outcome measures between studies
^kIndirectness due to substantial differences in interventions between studies
^lImprecision due to the sample size in the meta-analysis being lower than the optimal information size criterion and/or the 95% CI of the effect size overlapping zero effect
^mEvidence for publication bias due to a very small number of studies (k < 5)

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ISSN: 2052-1847

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