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

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 maximize myofibrillar muscle protein synthesis, but not
mitochondrial muscle protein synthesis, after endurance exercise [4]. It is
reasonable to suggest that mitochondrial muscle protein synthesis is most
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.

To define a dose-response relationship after intrinsically labeled milk protein
ingestion on myofibrillar and mitochondrial muscle protein synthesis after a
single bout of endurance exercise.

Parallel design, randomized, placebo controlled, double blind.

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.

The risks involved in participating in this experiment are minimal. Insertion
of the catheters in a vein is comparable to a normal blood draw and the only
risk is a small local hematoma. This is also true for muscle biopsies. Muscle
biopsies will be taken through a small (5 mm) incision, following local
anaesthetic of the skin and muscle fascia, and will heal completely. Muscle
biopsies will only be obtained by an experienced physician. The labeled,
non-radioactive amino acids tracers that will be infused intravenously are
produced according to GMP standards and are safe for human use. There is no
risk associated with the DEXA scan. The radiation dose emitted during a DEXA
scan is 0.001 mSv. This is a very low exposure compared to the total background
radiation in the Netherlands, which is ~2.5 mSv/year. For comparison, the
radiation dose during a flight higher than 10 km is 0.005 mSV*h-1.