Effects of Acute Carbohydrate–Electrolyte Supplementation on Exercise Performance in Moderate-to-Hot Ambient Conditions: A Systematic Review and Meta-Analysis

Background: An ambient-temperature eligibility criterion of ≥22 °C was treated as an operational lower boundary spanning moderate or mildly warm to hot conditions, not as a universal physiological threshold for heat stress. This systematic review and three-level meta-analysis evaluated acute carbohydrate–electrolyte (CHO-E) supplementation versus a water or non-caloric placebo during exercise at these temperatures. Methods: Following PROSPERO registration (CRD420261410953), five databases were searched to May 2026 for randomized controlled trials. Nested effect sizes were synthesized using three-level random-effects models (Hedges’ g), and certainty was evaluated with RoB 2 and GRADE. Results: A secondary omnibus synthesis included 32 effect sizes from 21 studies (N = 316) and yielded a small positive average estimate (g = 0.37, 95% CI: 0.21 to 0.53; p < 0.001; I2 = 46.7%), although the 95% prediction interval crossed the null (−0.21 to 0.96). Primary outcome-domain analysis identified a positive average estimate for aerobic endurance (g = 0.45, 95% CI: 0.26 to 0.64), whereas evidence for anaerobic endurance, explosive power, and strength remained inconclusive. Post hoc threshold sensitivity analyses retained positive mean estimates after excluding trials at 22–25 °C (>25 °C: g = 0.41, 95% CI: 0.23 to 0.59) and at ≥28 °C (g = 0.36, 95% CI: 0.11 to 0.61), but both prediction intervals crossed zero. Neither ambient temperature nor exposure duration was a significant linear moderator. Conclusions: Acute CHO-E supplementation was associated with a small average performance difference, concentrated in aerobic endurance, within the specified ambient-temperature range. Because the trials compared treatments within the same environmental condition rather than hot with thermoneutral exercise, these results do not establish that CHO-E offsets heat-induced performance decrements.