The impact of collagen peptide versus free amino acid ingestion on myofibrillar and connective tissue protein synthesis rates at rest and during recovery from exercise

Dietary protein ingestion stimulates muscle protein synthesis rates and further
augments the muscle protein synthetic response to a single bout of exercise.
The anabolic properties of dietary protein ingestion appear to be largely
attributed to the post-prandial rise in circulating plasma essential amino acid
concentrations, with leucine being of particular interest. In support, protein
supplementation during recovery from exercise has been shown to augment the
gains in muscle mass and strength following more prolonged exercise training .
Stable isotope methodology is generally applied to assess the impact of protein
ingestion on muscle protein synthesis rates in vivo in humans. Incorporation
rates of stable isotope labeled amino acids in muscle tissue are assessed
following primed continuous labeled amino acid infusions at rest or during
recovery from exercise. The focus is generally directed towards the
post-prandial increase in the synthesis rates of contractile muscle protein,
referred to as myofibrillar protein. As a consequence, there is little
information on the impact of nutrition and exercise on the synthesis rates of
connective tissue protein in skeletal muscle. The collagenous extracellular
matrix of muscle tissue has recently regained much interest for its key role in
transferring the forces generated by the contractile filaments throughout the
muscle and onto the ligaments, tendons, and bone. This connective tissue matrix
has been shown to express a high level of plasticity and collagen protein
synthesis rates have been shown to rapidly increase in muscle tissue following
exercise. However, the impact of protein ingestion with or without prior
exercise on connective tissue protein synthesis rates in muscle remains to be
established.
Dairy protein is often considered the preferred protein source to maximize
myofibrillar protein synthesis rates. However, dairy protein contains
relatively little glycine and proline and may, therefore, be ineffective to
support an increase in connective tissue protein synthesis rates at rest or
during recovery from exercise. Recently, we demonstrated that milk protein
ingestion actually lowers plasma glycine availability, implying that connective
tissue remodeling during recovery from exercise may be compromised by low
plasma glycine availability. A promising alternative are collagen peptides,
which are rich in glycine and proline and have, therefore, been proposed as the
preferred protein source to support connective tissue remodeling. While the
impact of collagen peptide ingestion on connective tissue protein synthesis
rates in skeletal muscle and skin tissue remains to be established, recent
studies have reported that collagen peptide supplementation can further augment
skeletal muscle mass and strength gains following prolonged exercise training.
Furthermore, it has been suggested that collagen peptides have anabolic
properties that extend beyond the provision of their corresponding amino acid
precursors. Whether collagen peptides contain specific bioactive peptides that
can further stimulate myofibrillar and/or connective tissue protein synthesis
rates in muscle and skin has never been addressed in vivo in humans.

To assess the impact of collagen peptides versus free amino acids on
myofibrillar and connective tissue protein synthesis rates in muscle and skin
obtained during recovery from exercise and rest in vivo in humans.

Double-blind, parallel-group, placebo-controlled intervention study

Participants will perform unilateral resistance exercise followed by the
ingestion of either 30 g of collagen peptides, 30 g free amino acids (matching
the profile of collagen peptides), or a non-caloric placebo (flavored water).
Continuous intravenous tracer infusion will be applied, and plasma, muscle and
skin samples will be collected in order to assess the muscle and skin protein
synthetic response.

The burden and risks involved in participating in this experiment are small.
Insertion of the catheters in a vein is comparable to a normal blood draw and
the only risk is a small local hematoma. Muscle and skin biopsies will be
obtained under local anesthesia by an experienced physician. The muscle biopsy
may cause some minor discomfort, which is comparable to muscle soreness or the
pain one has after bumping into the corner of a table. The area of the skin
biopsy might feel a bit uncomforable the next days, but will only result in
minor discomfort. During the experimental trial 17 blood samples (~170mL total)
will be obtained. The total amount of blood collected is less than half the
amount of a blood donation and will be completely restored in approximately 1
month. The stable isotope amino acids tracers that will be infused
intravenously during the experimental trial are produced according to GMP
standards and are safe for human use. Participants will be instructed on proper
utilization of the exercise equipment by the researcher to prevent injury.
Participants will visit the University two times. The first visit will involve
a screening visit (3 h), during which the eligibility of the participant will
be assessed and a DEXA scan will be performed. Additionally, participants will
be familiarized with single leg exercise on the leg press and leg extension
machine. The single leg one repetition maximum (1RM) will be determined on the
same machines. For the second visit (experimental trial) participants are
required to come to the University in a fasted state, not having consumed any
food or beverages (except for water) as from 22:00 the evening before. Also, 2
days prior to the experimental trial participants need to record their food
intake and activities performed. During these 2 days participants are not
allowed to perform heavy physical exercise or drink alcohol. Filling out the
food and activity log properly will take the participant 30-45 min each day.
There is no direct benefit for the participants, except from their contribution
to scientific knowledge.