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Slowing Muscle Protein Breakdown

Dr. Robert Portman, a prominent sports science researcher, is coauthor of Nutrient Timing and Performance Zone. His latest book is Hardwired for Fitness.


Misconception about building muscle = only stimulate protein synthesis.

Anabolism (building new muscle protein) and catabolism (breaking it down) are constant and dynamic processes.

Key: net protein balance.

Protein synthesis is greater than protein breakdown = net positive balance and an increase in muscle.

Protein breakdown is greater than protein synthesis = net negative protein balance and a decrease in muscle.

Most athletes are at a balance = neither increasing nor decreasing muscle.

Endurance athletes’ goal should be to increase muscle.

Moderate to intense exercise increases protein breakdown due to two factors: The increase in 1) 

Cortisol and 2) reactive oxygen species (R.O.S.)

Cortisol increases due to physical stresses such as dehydration and the body seeking ways to provide fuel to the working muscles.

30 minutes+ of moderate to intense exercise can use up to 20% of energy coming from protein.

During aerobic exercise higher levels of R.O.S. increase protein breakdown due to the activation of specific enzyme pathways.

There are a number of mechanisms that slow protein breakdown:

  1) Insulin = acts as a powerful anabolic agent for building muscle in two ways:

      a) stimulates protein synthesis by turning on mTOR (protein synthesis activator).

      b) Helps transport amino acids to the cells where they can manufacture muscle.

One of the most overlooked benefits of insulin is slowing protein breakdown to help create a net increase in muscle.

 2) Recovery nutrition. Because cortisol and R.O.S. increase following exercise a combo carb,

       protein, and electrolyte drink that has antioxidants can also slow muscle breakdown by:

       a) Electrolytes rehydrate and thus decrease cortisol levels.

       b) Carbs increase insulin which increases protein synthesis and reduces cortisol.

       c) Protein provides the raw material for the rebuilding and repair of muscle.

       d) Antioxidants decrease R.O.S.

       e) The recovery drink Endurox R4 is an excellent choice for the post exercise regimen.

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