Abstract
A higher protein intake is recommended for athletes compared to healthy non-exercising individuals. Additionally, the distribution and quality (i.e., leucine content) of the proteins consumed throughout the day should be optimized. This study aimed to determine the nitrogen balance and distribution of protein and amino acid intakes in competitive swimmers during the general preparation phase. Thirteen swimmers (age: 19.7 ± 1.0 years; VO2max: 63.9 ± 3.7 mL·kg−1·min−1, mean ± standard deviation) participated in a five-day experimental training period. Nutrient intakes were assessed using dietary records. Nitrogen balance was calculated from the daily protein intake and urinary nitrogen excretion. The intake amounts of amino acids and protein at seven eating occasions were determined. The average and population-safe intakes for zero nitrogen balance were estimated at 1.43 and 1.92 g·kg−1·day−1, respectively. The intake amounts of protein and leucine at breakfast, lunch, and dinner satisfied current guidelines for the maximization of muscle protein synthesis, but not in the other four occasions. The population-safe protein intake level in competitive swimmers was in the upper range (i.e., 1.2–2.0 g·kg−1·day−1) of the current recommendations for athletes. The protein intake distribution and quality throughout the day may be suboptimal for the maximization of the skeletal muscle adaptive response to training.
Highlights
Swimming is a sport demanding muscle strength and endurance capacity underpinned by different combinations of anaerobic and aerobic fuel systems
Because amino acids are oxidized as energy sources at ~ 4.4% or 10% of the total exercise-induced energy expenditure in a carbohydrate-loaded or carbohydrate-depleted state, respectively [4], they have to be replaced by dietary protein and amino acid intakes
We investigated the nitrogen balance (NBAL) in competitive collegiate swimmers during the general preparation phase with analysis of protein and amino acid intake at each eating occasion, and estimated the average protein intake for zero NBAL and population-safe protein intake to be
Summary
Swimming is a sport demanding muscle strength and endurance capacity underpinned by different combinations of anaerobic and aerobic fuel systems. To improve their endurance capacity, competitive swimmers generally participate in a large volume of endurance training in combination with low-intensity and high-intensity exercise [1]. Because amino acids are oxidized as energy sources at ~ 4.4% or 10% of the total exercise-induced energy expenditure in a carbohydrate-loaded or carbohydrate-depleted state, respectively [4], they have to be replaced by dietary protein and amino acid intakes. Some studies have indicated that competitive swimmers may not consume enough energy to meet their energy expenditure [3,5,6]. Since changes in protein metabolism result in increased protein requirements during energy deficit [7,8,9], competitive swimmers with higher training volumes may require higher
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