Protein hydrolysate versus intact protein intake as means to promote muscle protein anabolism: fiber-type specific effects of exercise?

Food intake and in particular the ingestion of protein or amino acids has been
shown to be powerful stimulus to promote net muscle protein anabolism. The
quantity and quality of the ingested protein strongly modulate protein
metabolism. It has been speculated that the ingestion of a protein hydrolysate
would be more effective in promoting muscle protein anabolism compared to the
ingestion of an intact protein source. However, scientific evidence to support
the proposed differences in the metabolic response to the ingestion of an
intact protein or its hydrolysate remains to be established in vivo in humans.
Besides nutrition, exercise has been shown to be a powerful stimulus to promote
muscle protein synthesis. The activation of muscle protein synthesis following
resistance exercise has been suggested to be muscle fiber-type specific.
However, there is no data available in humans whether the exercise stimulus is
necessary to attain maximal muscle protein synthesis rates or that the intake
of protein is already enough to maximally stimulate protein synthesis. In
addition, in vivo measurements of muscle protein synthesis rates following
exercise in type I and II muscle fibers are not available yet.

The first aim of this proposal is to determine the surplus value of the
ingestion of a protein hydrolysate compared to an intact protein as a means to
improve protein digestibility, to maximize plasma amino acid availability
and/or to stimulate muscle protein anabolism. The second aim of this proposal
is to study the additional effect of resistance exercise in the stimulation of
protein synthesis by protein intake. In addition we aim to investigate, whether
protein synthesis rates are different between muscle fiber-types following
resistance exercise.

Muscle protein synthesis will be measured using stable isotope methodology
following the ingestion of either an intrinsically label protein hydrolysate or
intact protein (study A), following one legged resistance exercise with protein
supplementation (study B), and following resistance exercise in type I and II
muscle fibers (study C). This study design will be used to determine the
surplus value of the ingestion of a protein hydrolysate (study A), the
execution of resistance exercise (study B) in stimulating muscle protein
synthesis. In study C we will determine fiber-type specific muscle protein
synthesis rates.

Study A: intake of protein hydrolysate versus intact protein
Study B: resistance exercise versus rest
Study C: resistance exercise

The risks involved in participating in this experiment are minimal. Insertion
of the catheters in a vein is comparable to a normal blood drawn and the only
risk is of a small local hematoma. This is the same for the muscle biopsy. The
incision made for obtaining the muscle biopsy will be done by an experienced
physician and will heal completely. The labeled amino acids tracers applied in
this experiment are not radioactive and are completely safe. De test beverages
are made from normal nutritional ingredients and for this reason do not form
any health risks.

Screening 3 h
1RM test 0.5h (study B and C)
Visiting University 8 (study B and C)-16h (study A)

For study A subjects will visit the university 19h, for study B and C subjects
will visit the University for 11.5 h