Carbohydrate-Restricted Exercise With Protein Increases Self-Selected Training Intensity in Female Cyclists but Not...

Area of Science:

• Exercise Physiology
• Sports Nutrition
• Human Performance

Background:

• Carbohydrate-restricted training can impair blood glucose levels and exercise intensity.
• Strategies are needed to maintain performance during low-carbohydrate exercise.

Purpose of the Study:

• To investigate the effects of casein protein hydrolysate ingestion on exercise performance and physiological responses in overnight-fasted athletes.
• To determine if protein supplementation can aid carbohydrate-restricted training.

Main Methods:

• Double-blind, randomized crossover study with 24 athletes (male runners, male cyclists, female cyclists).
• Athletes ingested casein hydrolysate or placebo during incremental tests, steady-state exercise, and a time trial.
• Measured metabolic demand, heart rate, rating of perceived exertion (RPE), glycemia, and time trial performance.

Main Results:

• Protein ingestion increased metabolic demand and heart rate in male athletes but not female cyclists.
• Carbohydrate oxidation increased with protein in female cyclists only.
• Glycemia was maintained in runners but increased with protein; it was maintained in cyclists.
• Time trial performance was compromised in runners, unchanged in male cyclists, and improved in female cyclists.

Conclusions:

• Casein hydrolysate during carbohydrate-restricted exercise maintains glycemia in runners and cyclists.
• It enhances metabolic demand in male athletes and carbohydrate oxidation in female cyclists.
• This strategy may improve carbohydrate-restricted training intensity in female cyclists but not male endurance athletes.