Maximizing Muscle Growth


This lecture is all about building muscle mass, a topic that will become especially important in lecture 10!

In this lecture, we’ll discuss the processes of muscle protein synthesis, muscle protein breakdown, and how BOTH are critical for overall muscle health.

We’ll talk about how much protein is needed, when we need to consume it, and what sources are the best options. In particular, we’ll focus on the role of the amino acid leucine in stimulating the mTORC1 pathway. This will lead to a discussion on BCAAs and why they may not be quite the supplement that everyone wants them to be.

Key Results

At the end of this lecture, you should be able to:

  • Understand the processes of muscle protein synthesis and breakdown
  • Define guidelines for maximizing MPS through protein consumption
  • Explore the role/importance of BCAA
  • Discuss practical recommendations for protein intake to maximize MPS

Key terms

Key terms we will cover:

Muscle Protein Synthesis

Simply the process of building new proteins within muscle fiber

  • Think of adding bricks to a wall
    • Muscle is the “wall”
    • Each brick is a new protein
  • However, bricks are also being taken away
  • Add more bricks than you take away = bigger muscles
  • Remove more bricks than you add = smaller muscles


  • Insulin, eating, training Muscle Protein Breakdown
  • insulin, fasting, inactivity

Muscle Protein Breakdown

  • We WANT muscle protein breakdown to occur
  • Muscle proteins are damaged by exercise, general metabolism, inflammation
  • Recycling of these proteins into amino acids, and back into new proteins improves overall muscle function
  • Mice genetically engineered to prevent proper break down of muscle protein are weaker and smaller than normal mice
  • Muscle protein breakdown is very, very similar across almost all biological situations
  • Small amounts of food, specifically carbs, inhibit muscle protein breakdown maximally
  • Complex meals, with slower digestion/absorption rates may have advantages as suppressing MPB
  • Long term fasting and complete lack of training are the major “gas pedals” for break down

Maximize MPS

  • 20 gram of protein gives a near-maximal increase in MPS after lower body resistance training
  • 40g increases the rate by ~10%, with excess protein being oxidized
    • converts it for use of energy production
  • FULL body was trained in the workout sessions, versus performing an upper or lower body split. While more research will be needed to confirm the hypothesis, one could argue that with full body training, greater protein intake is required to maximize MPS

Protein source matters

  • Different protein sources have different abilities to stimulate MPS

    • Key factors include how fast it is digested/absorbed and the amino acid composition
  • Casein is a slower digesting protein, and has a lower essential amino acid content than whey protein

    Essential amino acids are the acids we can’t generate in the body

  • The digestion speed and leucine content are thought to be two of the more critical aspects that determine MPS rates

plant protein has less essential amino acids.

leucine and the mTORC1 pathway

3 ways to stimulate it

  • leucine
  • muscle contraction
  • insulin

want to take complete proteins. Leucine drives the mTORC1 pathway but all are needed

What about BCAAs

BCAAs only help when you are low on Leucine.. in vegetarian and vegan people

“A physiologically-significant increase in the rate of muscle protein synthesis requires adequate availability of all amino acid precursors. The availability of the other EAAs will rapidly become rate limiting for accelerated protein synthesis. Consistent with this perspective, the few studies in human subjects have reported decreases, rather than increases, in muscle protein synthesis after intake of BCAAs. We conclude that dietary BCAA supplements alone do not promote muscle anabolism”

  • Journal of the International Society of Sports Nutrition August, 2017

Protein Timing / The Anabolic Window

  • Evidence supporting “protein timing” is a study where consuming protein immediately after training was more effective than protein ingestion 3 h post- exercise
  • In contrast, a different study observed no difference in MPS was found when essential amino acid were ingested 1 h or 3 h post-exercise

“ With respect to hypertrophy, total protein intake was the strongest predictor of ES magnitude. These results refute the commonly held belief that the timing of protein intake in and around a training session is critical to muscular adaptations and indicate that consuming adequate protein in combination with resistance exercise is the key factor for maximizing muscle protein accretion.”

Practical application of protein timing

  • Minimum of 1.6 g protein/kg BW
  • Maximum of 2.2 g protein/kg BW
    • Divide that total protein intake into 4 servings spread throughout the day
  • In the meal that follows training, increase your protein intake by an additional 20 grams to account for the fact that strength training delays the “muscle-full effect”
  • For other meals, try and focus on using more complex protein options than protein powders to allow for a more consistent stream of amino acids into the body to potentially reduce muscle protein breakdown

Muscle protein synthesis - role of carbs

  • Insulin has been reported to stimulate skeletal MPS in mice, rats and human, however other studies show no impact
    • We know that insulin treatment increases mTORC1 signaling
    • But insulin also increases blood flow to skeletal muscle as well though, increasing the amount of amino acids that flow to the muscle
    • This fact makes it very difficult to determine whether insulin stimulates human skeletal muscle protein synthesis directly, indirectly, or both

Muscle protein synthesis - role of fat

  • Despite claims that it will massively slow digestion, fat intake with protein does not appear to slow down MPS at all

MPS on Training

  • Multiple sets of the same exercise induce more MPS than a single set
  • For maximal MPS, the set must be performed for reps ”close to failure”
  • Longer rest between sets increases MPS (3-5 min appears to be an optimal window)
  • Each muscle group should be trained 2X per week as a single bout of resistance exercise can stimulate muscle protein synthesis for longer than 72 hour, but peaks at 24 h

Notes mentioning this note

Join the Newsletter