Background and aim: Co-ingestion of carbohydrate and protein supplement (CHO-PRO) is a common strategy to enhance endurance performance. However, the optimal dose-response relationship has not been established, which limits evidence-based nutritional guidance for individuals. This study aimed to characterize the performance dose-response curve of a 4:1 CHO-PRO during prolonged rowing. Methods: In a randomized, double-blind, parallel-group trial, 171 physically active male university students (age: 23±2years) from non-sports majors each completed a single experimental session. Each session involved a rowing protocol consisting of two 30-min bouts. During the exercise, participants consumed one of eight distinct doses of a 4:1 CHO-PRO in aliquots every 15min. The CHO delivery rates ranged from 0.5 to 1.2g/kg/h. Total rowing distance served as the primary performance outcome and was analyzed using a one-way ANCOVA with baseline countermovement jump as a covariate. Result: A significant quadratic (U-shaped) dose-response relationship was found for rowing performance. The lowest dose CHO-PRO (0.5g/kg/h CHO) resulted in significantly greater rowing distance compared to several higher doses (0.9-1.2g/kg/h). No significant main effect of supplement dose was observed for heart rate, blood lactate, blood glucose, or rating of perceived exertion during exercise. Post-exercise recovery markers also did not differ significantly between the groups. Conclusion: For prolonged rowing, a lower dose of the CHO-PRO was more effective than higher doses, revealing a non-linear performance response. This non-linear response was characterized by significant performance decrements at several higher intake levels. These findings underscore the importance of dose optimization. Exceeding a certain intake threshold may impair endurance performance.
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