The effects of protein dose response on myofibrillar and mitochondral protein synthesis after endurance exercise in young men

Rationale: Dietary protein intake after exercise is necessary to maximally stimulate muscle protein synthesis rates [1]. Previous studies have shown that the ingestion of 20 grams of both egg and whey protein is sufficient to maximize both mixed and myofibrillar muscle protein synthesis after resistance type exercise [2, 3]. In addition, it has been observed that 20 grams of protein intake is sufficient to stimulate myofibrillar muscle protein synthesis, but not mitochondrial muscle protein synthesis, after endurance exercise [4]. It is reasonable to suggest that mitochondrial muscle protein synthesis may be particularly important for endurance athletes, as it will improve the oxidative capacity of the skeletal muscle in this athletic population. It remains to be elucidated whether higher doses (>20 grams) of protein ingestion are necessary to enhance mitochondrial muscle protein synthesis rates after endurance exercise. In addition, the effects of different doses of milk protein, as source of dietary protein, have never been tested on myofibrillar and mitochondrial muscle protein synthesis after endurance exercise. We aim to fill these gaps in our understanding.
Objective: To define the dose-response relationship after intrinsically labeled milk protein ingestion on whole-body, myofibrillar, and mitochondrial muscle protein synthesis after a single bout of endurance exercise in young men.
Study design: Parallel design, randomized, placebo controlled, double blind.

Study population: 48 young (20-30 y inclusive) healthy males.

Intervention (if applicable): Subjects will perform endurance exercise and consume a combination of carbohydrate (45 gr) and different doses of intrinsically labeled milk protein (0, 15, 30, 45 gr). In addition, continuous intravenous tracer infusions will be applied, with plasma and muscle samples collected.

Main study parameters/endpoints: Primary: myofibrillar, and mitochondrial protein bound [13C6] phenylalanine and [13C6] leucine enrichments. Secondary: plasma glucose, insulin, leucine, phenylalanine, tyrosine, plasma [13C6]phenylalanine, plasma [13C6] leucine, plasma D5-phenylalanine and plasma (3,5-D2)-tyrosine enrichments.

30 grams of dietary protein ingestion is necessary to maximize whole-body, myofibrillar, and mitochondrial muscle protein synthetic response after a single bout of endurance exercise in healthy young males. Lower doses of protein (ie. 0 and 15 g) will be suboptimal while higher doses (ie. 45 g) will not induce a greater protein synthetic response.

t=0 drink; t=0 h, t=3 h, t=6 h skeletal muscle biopsies; 14 blood draws

exercise bout and protein drink with different doses