Researchers have demonstrated that consumption of carbohydrate-protein-electrolyte solutions during prolonged endurance exercise enhances performance, but the effects of these supplements on short-term swim exercise are unclear. Purpose: To quantify the effects of carbohydrate-protein-electrolyte supplementation on performance, ratings of muscle soreness and ratings of coping with exercise in swimmers. Methods: In a double-blind randomized crossover with a 1-wk washout, 13 highly-trained swimmers (6 females and 7 males; age 17-23 y) consumed either carbohydrate-protein-electrolyte or non-caloric fl avored water before and during an incremental 7x200-m step-test, and 10 min before a 100-m time-trial 24 h later. Diet and training were standardized. Earlobe blood samples were taken to measure lactate and glucose concentrations. We also assessed subjective ratings of soreness and coping with exercise. We used magnitude-based clinical inferences for effects on performance and subjective ratings, and mechanistic inferences for effects on lactate and glucose concentrations. Results: The supplement had clinically clear performance effects that were potentially harmful and unlikely to be benefi cial: time in the last step of the steptest, 0.9% (90% confi dence limits ±2.0%); lactate-threshold time, 0.2% (±1.3%); and 100-m time-trial time, 0.1% (±0.6%). The supplement increased blood glucose moderately in the step-test, by 7.4% (±4.0%). Effects of the supplement on muscle soreness and coping with exercise in the step-test and time-trial were possibly harmful and very unlikely to be benefi cial. Conclusion: The carbohydrate-protein-electrolyte supplement should not be used in short-term swim performance tests or races.
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