Background: While caffeine may lower ratings of perceived exertion (RPE) or increase power output at a given RPE, whether caffeinated gum produces these effects during perceptually regulated exercise remains unclear. Aim: This study examined whether caffeinated gum increases self-selected cycling output at regulated-RPE in well-trained male athletes. Methods: Twelve well-trained male athletes (age: 21 ± 2 years; body mass: 77.3 ± 6.0 kg; VO_2peak: 47 ± 4 mL/kg/min) completed randomized, double-blind, placebo-controlled crossover trials separated by 7 days. Athletes chewed caffeinated gum (6 mg/kg) or placebo for 15 min before two 10 min cycling stages at RPE 4 and 7 (0–10 OMNI Scale). Cadence, power output, oxygen uptake, heart rate, and blood lactate concentration were measured. Results: Caffeinated gum significantly increased cadence (RPE 4: 72 ± 7 vs. 66 ± 10 rpm, p = 0.02; RPE 7: 77 ± 9 vs. 71 ± 11 rpm, p = 0.04), total work (53 ± 10 vs. 48 ± 10 kJ, p < 0.01; 87 ± 12 vs. 77 ± 14 kJ, p < 0.01), mean power output (88 ± 16 vs. 79 ± 16 W, p < 0.01; 146 ± 20 vs. 129 ± 24 W, p < 0.01) and peak power output (97 ± 18 vs. 88 ± 17 W, p < 0.01; 166 ± 27 vs. 147 ± 29 W, p = 0.01). Oxygen uptake was also higher in the caffeine condition at both RPE 4 (1.58 ± 0.12 vs. 1.42 ± 0.16 L/min, p = 0.005) and RPE 7 (2.17 ± 0.25 vs. 2.01 ± 0.22 L/min, p = 0.045), whereas heart rate and blood lactate concentration did not differ significantly between conditions (p > 0.05). Conclusion: Caffeinated gum (6 mg/kg) enhances self-selected cycling work at prescribed RPEs, indicating that it alters perceptually regulated exercise intensity in well-trained males.

Background/Objectives: This meta-analysis aimed to quantify the combined ergogenic effects of caffeine (CAF) and carbohydrate (CHO) on high-intensity interval exercise (HIIE) performance and to identify potential moderating factors. Methods: Four databases were systematically searched to identify randomized crossover trials assessing CAF combined with CHO (CAF + CHO) on HIIE performance (i.e., exercise time, distance, or total work). A three-level random-effects meta-analysis was performed to calculate pooled Hedge’s g (g) values. Moderator effects were explored through subgroup analyses, including control group (placebo-, CHO-, and CAF-controlled), CHO administration (mouth rinse and ingestion), and training status (recreationally active and trained). Results: Eleven studies met the inclusion criteria (n = 105; 8 female). CAF + CHO significantly enhanced HIIE performance (g = 0.44, 95% CI: 0.23–0.66). Subgroup analyses indicated that CAF + CHO mouth rinsing (g = 0.91, CI: 0.49–1.33) yielded superior effects compared to CAF + CHO ingestion (g = 0.33, CI: 0.14–0.52) (p for subgroup < 0.05). Performance improvements with CAF + CHO were observed for CHO- and placebo-controlled trials, but not in CAF-controlled trials, without significant subgroup effects (p for subgroup > 0.05). Importantly, evidence of publication bias was identified, and the overall certainty of evidence was graded as low according to the GRADE framework. Conclusions: CAF + CHO appears to be effective for enhancing HIIE performance, with greater benefits observed when CHO is administered via mouth rinsing rather than ingestion. Preliminary evidence suggests that CAF may play a key role in CAF + CHO strategies. However, given the limited number of female participants, the generalizability of these findings to both sexes is limited. Additional high-quality trials are needed to establish more definitive recommendations.

Objectives: We quantified the influence of acute caffeine (CAF) supplementation on CrossFit performance and physiological outcomes and examined potential effect modifiers. Methods: Randomized crossover studies involving CAF supplementation in CrossFit were identified through systematic searches of multiple electronic databases. Performance effect sizes were expressed as Hedges’ g and pooled within a three-level random-effects framework, while physiological outcomes were synthesized using conventional two-level models. Effect modification was examined across training status (recreationally active vs. trained) and CAF delivery form (capsule vs. beverage). Meta-regression was additionally used to assess whether relative CAF dose was associated with changes in CrossFit performance. Results: The final synthesis comprised seven studies with 103 participants, including 13 women. A small favorable effect of CAF was found for overall CrossFit performance (g = 0.13, 95% CI: 0.05–0.22), accompanied by a higher blood lactate concentration (g = 0.53, 95% CI: 0.23–0.82). Stratified estimates favored CAF in recreationally active participants (g = 0.20, 95% CI: 0.06–0.34) and when administered in capsule form (g = 0.17, 95% CI: 0.06–0.29); nevertheless, evidence for between-subgroup differences was absent (all p subgroup > 0.05). The relative CAF dose did not explain variation in performance effects in either the linear (β₁ = 0.04, p = 0.570) or nonlinear model (β₂ = −0.004, p = 0.578). Conclusions: The available evidence suggests a small ergogenic benefit of acute CAF supplementation for selected CrossFit performance outcomes, accompanied by elevated blood lactate concentrations. Subgroup analyses revealed no significant moderating effect of training status and supplementation protocols. However, the limited number of studies and predominance of male participants warrant cautious interpretation. Future research should prioritize larger randomized controlled trials, greater representation of female athletes, and more standardized CrossFit performance protocols.

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.