Protein ingestion prior to sleep as a dietary strategy to improve post-exercise, overnight recovery

Resistance type exercise training stimulates both muscle protein synthesis and
breakdown rates. A single bout of resistance type exercise has been shown to
stimulate muscle protein synthesis for up to 48 hours. However, in the absence
of food intake muscle protein breakdown exceeds protein synthesis rates.
Protein ingestion during immediate post-exercise recovery stimulates muscle
protein synthesis, inhibits protein breakdown, leading to net muscle protein
accretion.
So far, only few studies have focused on muscle protein synthesis during
overnight recovery. Previous work by Tipton et al suggests that 24h net protein
balance reflects the acute anabolic response to a single bout of exercise.
However, recent work from our laboratory showed that post-exercise muscle
protein synthesis rates during overnight sleep are close to basal fasting
levels. Therefore, we hypothesise that muscle protein synthesis rates during
overnight recovery can be stimulated by providing sufficient amino acids during
the night.
We suggest that ingestion of a single bolus of intact casein represents an
effective dietary strategy to augment plasma amino acid availability during
sleep.

Allowing post-exercise muscle protein synthesis rates to be elevated during
overnight recovery might be of considerable relevance to both enhance the
benefits of exercise training in both athlete and clinical populations. For
example, stimulating muscle protein synthesis during the sleeping recovery
might augment muscle hypertrophy, increase mitochondrial mass, and/or improve
muscle tissue repair.

The present proposal is designed to assess the effects of protein ingestion
prior to sleep on muscle protein synthesis overnight in a practical setting.
After a full day on a standardized diet, subjects will perform an exercise-bout
in the evening. Casein or a flavoured placebo will be ingested 30 min prior to
sleep. We hypothesize that feeding casein prior to sleep will enhance muscle
protein synthesis rates during overnight recovery.

Subjects report to the lab and receive a standardized meal. A primed,
continuous infusion of isotopically labelled phenylalanine and tyrosine will be
inserted. A second Teflon catheter will be inserted in the contralateral hand
vein for arterialised blood sampling. The exercise protocol consists of a
lower limb resistance type exercise workout with 8 sets of 10 repetitions on
the horizontal leg press machine (Technogym BV, Rotterdam, The Netherlands) and
8 sets of 10 repetitions on the leg extension machine (Technogym BV, Rotterdam,
The Netherlands). The entire protocol will require ~45 min to complete. One
post-exercise drink (60 g carbohydrate and 20 g whey protein) will be provided
after cessation of exercise. At the end of the exercise protocol (t=0),
subjects will rest supine and a blood sample from the arterialised hand vein
and a muscle biopsy from the vastus lateralis muscle will be obtained. At 23.30
h subjects will receive the test drink and the second muscle biopsy will be
taken. Subsequently, subjects will rest supine until 24.00 h. This will be
followed by a sleeping period of 7 h. The third muscle biopsy will be obtained
at 7.00 h. Blood samples (8ml) will subsequently be taken from the arterialised
hand vein at t=-120, -60, 0, 30, 60, 90, 120, 150, 165, 180, 210 min and t= 4,
5, 6, 7, 8, 9, 10 hours. Muscle biopsies will be taken at t=0 h, 2,5 h and 10 h
post-exercise.

Subjects will ingest 500 ml water with or without 40 g intrinsically labelled
casein 30 min prior to sleep. L-[1-13C]phenylalanine was used to produce
intrinsically labeled milk proteins. Labeled proteins were obtained by infusing
a cow with L-[1-13C]phenylalanine, collecting milk and purifying the casein
fraction.

The risks involved in participating in this study are minimal. Insertion of the
catheters in a vein is comparable to a normal blood draw and the only risk is a
small local heamatoma. This is the same for the muscle biopsy. The incision
made for obtaining the muscle biopsy (performed by an experienced physician)
will heal completely. The labeled amino acids in both the infusion and in the
casein are stable (not radio-active) and therefore completely safe. The rest of
the food and drinks provided are normal foods or food ingredients and do not
impose health risks.