Protein intake is able to stimulate muscle
protein synthesis (MPS) above basal rates (1,2), and this response is greater if
combined with resistance training(3).
The muscle protein synthesis acute response from
exercise is a dose-response depending upon exercise intensity and workload (4).
At intensities
greater than 60% 1-RM, exercise increases MPS 2- to 3-fold (4); the latency for exercise
intensities of 6×8 repetitions at
75% 1-RM is <1 h (7). After a latent period after exercise of about 45 minutes to an hour MPS
rises sharply (2-3 fold) between 45 and 150 min (4).
In the rested, fasted state, skeletal muscle is in a
state of negative net protein balance (5). However, in response to amino acid
(AA) or protein feeding, MPS rates increase resulting in a positive net protein
balance (3,6). Over time the changes in fed and fasted periods and their
relative protein balances results in either skeletal muscle increase of
decrease (6).
The increased
sensitivity of MPS in response to essential aminoacid intake after exercise (3)
can last up to 24h (7), 24-48h (8,9) or even up to 72h (10). Therefore, repeated bouts of RE and protein feeding
result in skeletal muscle hypertrophy (11).
Available evidence points to a 20–25 g dose of high
quality protein to maximally stimulate MPS after resistance exercise in young
adults (1,2).
20g
Moore et al. (12) examined a protein dose response relationship with MPS
following RE. They fed whole-egg proteins after resistance exercise to young
men with training experience varying between 4 months to 8 years. The training
session consisted of a bout of
unilateral lower-body resistance exercise.
They fed participants drinks containing 0, 5, 10, 20,
or 40 g of whole egg protein after
exercise and measured protein synthesis from the vastus lateralis and
whole-body leucine oxidation over 4 h. MPS displayed a dose response to dietary
protein ingestion and was maximally
stimulated at 20 g with no statistically significant benefit with the
ingestion of 40g.
At 20 g protein (≈8.6 g EAAs) there was a ≈93% increase in mixed-muscle
FSR above the fasted condition; a dose of EAAs very similar to that seen at
rest (10 g) (13). A previous study also confirmed the same observation (21g vs.
40g) (14).
In another study by Witard et al. (15), ∼80-kg resistance-trained, young men performed a bout of unilateral exercise (8 × 10 leg presses
and leg extensions; 80% one-repetition maximum) and also ingested 0, 10, 20, or
40 g of whey protein isolate immediately (∼10 min) after exercise. They also measure MPS from the vastus lateralis muscle.
A 20-g dose of whey protein was sufficient to
maximally stimulate postabsorptive rates of myofibrillar MPS in rested and exercised muscle. A dose >20 g
stimulated amino acid oxidation and ureagenesis.
Similar results were also observed at rest (no exercise) using whole food;
30g of lean ground beef protein was just as effective as 90g at stimulating MPS
in young and elderly subjects (16).
The ceiling on MPS may in part be explained by what has been termed the “muscle full effect” (17). The “muscle
full” hypothesis (18) suggests an upper limit of AA delivery before muscle
cells would no longer respond and start diverting them toward oxidation (19).
After a lag of around 30 min there
is a large increase (∼3-fold) with MPS peaking around 1.5
h before returning to baseline by 2 h
(20,21) despite continued increased
availability of circulating amino acids and sustained ‘anabolic signaling’
(19,20) and about 3 hours long in response to a complete meal containing
protein, carbohydrates, and fats (22).
However there is some evidence to suggest that the muscle full effect or the refractory effect is delayed by exercise at least up to 6 hours (not clear what happens between 6h and 24h post-exercise) (8).
Nevertheless, it appears that 20g of whey protein (0.25gprotein/kg) is
sufficient to maximally stimulate MPS both at rest (13) and after exercise (23)
regardless of training status (15). Protein intake per dose above this threshold
is oxidized at a higher rate (12,15) and results in urea production (15).
But as other authors pointed out these
studies are limited to lower limb resistance training only and “thus it
remains unknown as to whether the absolute dose of protein required to
maximally stimulate rates of MPS following whole-body RE is >20g.” (1).
40g
The current thought is that the greater
the lean body mass and muscle mass the greater the protein dose necessary for
maximal stimulation of MPS (1,2,23). Another assumption is that the total
amount of muscle involved in the exercise bout also will influence the MPS
response.
Tipton et al. tested this hypothesis in
young, resistance-trained males by examining the response of MPS to two doses of whey protein ingested
following exercise involving a greater
amount of muscle mass, that is, a whole-body
exercise routine (24). The two groups also differed in LBM (≤65 kg LBM vs. ≥70 kg LBM). As with
previous studies, they also measure
MPS from the vastus lateralis muscle.
Results suggest that ingesting a 40 g dose of whey protein isolate
stimulated MPS to a greater extent than a 20 g dose of whey protein isolate
during acute 5h post workout, despite different amounts of LBM.
Note the individual
response, as always some respond better than others, in other words some may need more protein to get the same
response as others.
Specifically, “myofibrillar FSR was 20% higher with ingestion of 40 g
compared with 20 g of whey following whole-body resistance exercise,
irrespective of group”.
Authors believe the most likely
explanation for the results is the greater
amount of muscle activated during the exercise bout following whole body training, compared to a bout
of unilateral or bilateral leg resistance exercise in previous studies (12,15).
This challenges the general consensus that
ingestion of 20–25 g of protein after resistance exercise is
sufficient for the maximal MPS (1,2,23).
Resistance exercise enhances the delivery
of amino acids into the working muscle by increasing blood flow (3,5),
therefore the greater the amount of muscle worked during the training bout the
greater the amount of aminoacids taken up by the muscles (24).
But, since amino acid availability to any single muscle may be limited with whole-body
exercise, more protein is necessary
to elicit a higher MSP response to any single muscle worked (24).
And more importantly, because of this
authors pointed out that “mean FSR values are approximately 71% and 76% of the
FSR values for the 20 and 40 g, respectively, doses of whey protein that we
reported previously.”
Meaning that the
response to any single muscle trained following whole body training is lower
that if trained in a split fashion even if you take 40g of whey.
Following these observations, the
ingestion of 20 g of whey protein may be
insufficient after a whole-body resistance exercise for all muscles worked.
In the 40g trial there were more amino acids available for all the exercised
muscles and MPS measured in the legs likely was able to respond at a greater
rate, but still below previous studies
(at least for the vastus lateralis muscle) (24).
Authors concluded:
“Thus, it seems that the overall amount of
muscle mass possessed by the individual is a less important determinant of the
maximally effective dose of protein to ingest than the amount of muscle mass
activated during exercise. We conclude that more protein is necessary for the
increased stimulation of MPS following whole-body compared to unilateral or
bilateral resistance exercise. Moreover, it is not possible to determine the dose of protein necessary to stimulate a
maximal MPS response from our data. We examined the MPS response to two
amounts of protein only” (24).
So in practical
terms and in principle, if you want
to maximize the result or emphasize a specific muscle (perhaps lagging) you
have two options: doing do split
routines for that muscle, or
perhaps ingesting more than 40g of whey following a whole body training session
since more gets dispersed all over the body for all muscles worked.
Other populations
Diseased and older
populations have different protein requirements. Older adults have “anabolic
resistance” in response to ingestion of dietary protein and amino acids (25). As
a consequence of aging, MPS becomes refractory to hyperaminoacidemia, particularly
at lower protein intakes (26) meaning that healthy older men are less sensitive to low protein intakes and require a
greater relative protein intake up to 0.40 g/kg (27) in a single meal than young men to maximally stimulate postprandial
rates of MPS (27,28).
Keep in mind
this is the estimated average value, the acute protein intake may be as high as
0.60 g/kg for some older men (depending on contributing factors to the
“anabolic resistance” of MPS) and ~0.40 g/kg for some younger men (27).
A dysregulation of intracellular signaling
(14), a reduction in postprandial
nutritive blood flow (29), subclinical chronic
inflammation (30), a greater splanchnic
extraction of amino acids (31), and/or a reduction in habitual activity (32) are all contributor factors
that may account for the “anabolic resistance” of MPS with aging.
Other factors
independent of age are muscle disuse (32,33,34), disease status (30), and/or
lower quality protein with lower leucine content (35,36).
Interestingly, 113.4 g of lean
ground-beef patties can similarly
increase the mixed-muscle FSR in both the elderly and the young by ≈51%, suggesting
that a normal serving of beef provides enough AAs to overcome any deficiency in
responsiveness (37).
Short term should not be necessarily translated into
long-term gains
As noted before, the increase in MPS may be
sustained for up to 24h (7), 24-48h (8,9) or even up to 72h (10). Another point is that acute measures (1-6h post exercise) of MPS were
found not to be correlated with muscle
hypertrophy following chronic resistance training (38).
Muscle protein breakdown is also important for the
regulation of muscle hypertrophy on the long term, and the chronic (positive)
balance between MPS and MPB is more important than considering acute rises in
MPS.
It has been shown, as mentioned previously, a 50% increase
in MPB over 3 h of post-resistance exercise recovery (5). This MPB can be reduced by 30% in response to
20g of EAA + 30g or 90g of CHO
ingestion (39).
It is hard
to translate acute effects of protein timing on MPS to
chronic adaptations with exercise training. Several factors such as methods of
measuring protein utilization, training
status of subjects, exercise type and intensity, energy and carbohydrate
content of the diet, type and timing of protein intake, and duration of the
study all influence protein requirements (40).
New
methodologies for measuring cumulative MPS (C-MPS), such as the deuterium oxide
method should be applied to measure long-term responses in order to better
understand the dynamic fluctuations in protein requirements (40).
(41)
Repeated RE-T results in early muscle hypertrophy, ∼3–4 weeks, with any further progression relatively slow
in comparison, with increases in muscle size reported to be 5–15% by 8 weeks.
Cumulative response to RE-T measured using D2O have demonstrated ∼30% increases in MPS over 1 week, in which this
response becomes diminished with time and ensuing muscle hypertrophy (41).
Moreover, a meta-analysis examining protein timing and
hypertrophy concluded that that total
protein intake was the strongest predictor of muscular hypertrophy and that
protein timing did not influence hypertrophy (42).
Bottom line, when you perform sessions of whole body
training a 40g dose of whey protein might be more advantageous than 20g,
however total daily protein intake is still more important.
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