Effects of carbohydrate supplementation on the RPE-blood lactate relationship

PURPOSE:: To examine the effects of carbohydrate (CHO) ingestion on the RPE-blood lactate relationship during incremental and constant-effort exercise. METHODS:: Six male and three female subjects (mean age = 27.2 ± 8.2 yr, height [ht] = 174.5 ± 13.5 cm, weight [wt] = 68.9 ± 12.5 kg, body fat = 18.5 ± 8.3%), completed two incremental cycling lactate threshold (LT)/V̇O2peak tests followed by two 45-min production trials. Two hundred and forty milliliters of either carbohydrate or placebo (PL) was ingested before and every 15 min during exercise. RESULTS:: No differences were observed between conditions at LT, 2.5 and 4.0 mM, and peak. Within the CHO condition: V̇O2 = 25.0, 32.6, 37.5, 47.2 mL•kg•min; power output = 123.3, 170.7, 200.1, 241.7 W; RPE = 12.8, 15.4, 17.2, 19.3; and HR = 137.4, 156.8, 168.7, 187.7 beats•min at LT, 2.5 mM, 4.0 mM, and peak, respectively. Within PL: V̇O2 = 24.7, 32.5, 36.8, 45.7 mL•kg•min; power output = 130.0, 175.4, 201.9, 240.0 W; RPE = 12.1, 15.0, 17.0, 19.3; and HR = 134.9, 157.9, 169.6, 187.2 beats•min, respectively. In the CHO condition, blood glucose was higher (P < 0.001), and a trend was observed for lower RPE over time (P = 0.07). During the production trials (RPE of 16) in the CHO condition, higher blood glucose area under the curve (AUC) (PL: 204.1 ± 79.3 mM; CHO: 220.6 ± 18.5 mM; P = 0.039) and a trend for greater total work (PL: 448.5 ± 73.8 kJ; CHO: 470.5 ± 65.6 kJ; P = 0.089) were observed. CONCLUSIONS:: We conclude that 1) CHO ingestion does not alter the blood lactate-RPE relationship during incremental LT/V̇O2peak cycling; and 2) carbohydrate supplementation during exercise, eliciting high RPE, may increase work output during training sessions.