Recommended but Not High Carbohydrate Dose Improves Performance After Heavy- but Not Moderate-Intensity Exercise in Recreationally Trained Participants

This study determined: (i) whether carbohydrates (CHO) supplementation had beneficial effects on endurance performance, as assessed by a time trial (TT) test, following exercise bouts within either the moderate- or heavy-intensity exercise; and (ii) if above the recommended dose of CHO supplementation would impact endurance performance. Twelve recreationally trained males underwent: (i) a step-ramp-step test to estimate gas exchange threshold (GET) and maximal metabolic steady state (MMSS_est); (ii) 9 randomized visits consisting of 3 different constant power output (PO) bouts: within the moderate- (120 min at 90% of GET [MOD]); lower portion of the heavy- (90 min at Δ20% between GET and MMSS_est [HVY₁]); and higher portion of the heavy- (60 min at Δ80% between GET and MMSS_est [HVY₂]) intensity domain under 3 different conditions (placebo, recommended 40 g/h CHO [R-CHO], and high 90 g/h CHO [H-CHO]) dose per intensity with a subsequent 4 km TT. The 4 km TT was improved (p = 0.017) in the R-CHO (8.3 ± 0.7 min) compared to placebo (8.6 ± 0.9 min) after HVY₁ but not in the H-CHO (8.5 ± 0.9 min) condition. In contrast, 4 km TT performance was not different after MOD (placebo = 8.8 ± 1.3 min; R-CHO = 8.6 ± 1.1 min; H-CHO = 8.6 ± 1.1; p = 0.589) or HVY₂ (placebo = 8.8 ± 1.1 min; R-CHO = 8.6 ± 0.9 min; H-CHO = 8.7 ± 1.0; p = 0.465). In recreationally trained individuals, R-CHO supplementation improved 4 km TT performance following exercise within the lower portion of the heavy-intensity domains, but not following exercise in the moderate- or upper region of the heavy-intensity domain. Additionally, above-recommended CHO dose was no longer beneficial for performance regardless of the prior exercise intensity bout.