Muscle is in constant turnover: protein synthesis builds new tissue, protein breakdown removes damaged or unneeded tissue. The net difference determines whether muscle mass grows, holds, or shrinks. MPS is the primary lever trainees can influence.
The two MPS triggers:
- Resistance training stimulates MPS for roughly 24-48 hours after a session. The size of the response depends on training volume, intensity, and proximity to failure.
- Protein feeding stimulates MPS through amino acid availability, particularly leucine. The response saturates at roughly 0.4-0.55 g of protein per kg of body weight per meal in trained adults (the leucine threshold).
Combined, training-plus-feeding produces a stronger and longer MPS response than either alone. The post-training meal is when this combination is most evident; the pre-training meal partially fills the same role if recent enough.
What changes MPS rate:
- Higher per-meal protein dose (up to threshold)
- Higher leucine content (whey, dairy, eggs, lean meat)
- Recent training stimulus
- Adequate calorie availability (chronic deficits suppress MPS somewhat)
- Adequate sleep (sleep deprivation lowers MPS, supported by Phillips et al. work)
What does not meaningfully change MPS rate:
- Meal timing within the day (beyond the post-workout window discussion)
- BCAA-only supplementation (without other essential amino acids, MPS response is weaker than with whole protein)
- Carb intake at the protein meal (insulin's role in MPS is largely permissive at typical intakes; protein alone is enough)
Practical implications:
- Eat 25-40 g of high-quality protein per meal to consistently saturate MPS at each meal.
- Spread protein across 3-5 meals for cumulative MPS stimulation throughout the day.
- Train consistently to elevate the baseline MPS state; muscle gain is a long process.
- Sleep matters more than most lifters acknowledge. Chronic 5-6 hours of sleep meaningfully lowers MPS over weeks.