Muscle protein synthesis (MPS)

Muscle protein synthesis (MPS) is the production of new proteins in muscle, which grows only when synthesis exceeds protein breakdown over time.^{1Schoenfeld, Science and Development of Muscle Hypertrophy, 2nd ed., p. 18.} During a workout, synthesis is suppressed and breakdown rises.^{1Schoenfeld, Science and Development of Muscle Hypertrophy, 2nd ed., p. 18.} Afterward, synthesis climbs 2- to 5-fold, with effects lasting 48 hours or more.^{1Schoenfeld, Science and Development of Muscle Hypertrophy, 2nd ed., p. 18.} Repeating that stimulus with enough recovery allows muscle protein to accumulate.^{1Schoenfeld, Science and Development of Muscle Hypertrophy, 2nd ed., p. 18.}

Synthesis contributes much more to protein balance than breakdown does.^{2Haff and Triplett (eds.), Essentials of Strength Training and Conditioning, 4th ed., p. 228.} A larger short-term spike doesn’t necessarily predict more hypertrophy: in a 16-week study, the post-exercise rise didn’t predict who gained the most muscle.^{3Haff and Triplett (eds.), Essentials of Strength Training and Conditioning, 4th ed., p. 229.}

In practice

• In younger adults, 20 to 25 g of high-quality protein, containing 2 to 3 g of leucine, maximally stimulates synthesis after training.^{2Haff and Triplett (eds.), Essentials of Strength Training and Conditioning, 4th ed., p. 228.} Older adults may need 40 g or more.^{2Haff and Triplett (eds.), Essentials of Strength Training and Conditioning, 4th ed., p. 228.}
• Training keeps muscle sensitive to amino acids for 24 to 48 hours, but a meal’s effect lasts only 3 to 5 hours.^{3Haff and Triplett (eds.), Essentials of Strength Training and Conditioning, 4th ed., p. 229.} Aim for at least 20 to 30 g of protein every 3 to 4 hours.^{3Haff and Triplett (eds.), Essentials of Strength Training and Conditioning, 4th ed., p. 229.}
• For maximal muscle growth, Schoenfeld suggests 0.4 to 0.55 g/kg per meal across at least four meals, totaling 1.6 to 2.2 g/kg a day.^{4Schoenfeld, Science and Development of Muscle Hypertrophy, 2nd ed., p. 235.}
• Older clients show anabolic resistance, a blunted synthesis response to resistance exercise.^{5Schoenfeld, Science and Development of Muscle Hypertrophy, 2nd ed., p. 181.}