Most of us know that protein makes up the cellular structure of our muscles and provides many other functions in our body, so it is obviously quite important. Proteins can function as enzymes, antibodies, transport molecules and provide structural support to our cells. It makes up collagen which is found in our bones and without strong bones, we would be more prone to stress fractures from the impact of running. Muscle is one of the prime examples of where proteins function to grow and repair muscle fibres which have formed microtears from the stress of running.

The protein that you eat, does not directly convert into muscle protein. First, it is broken down into amino acids and then the DNA in your cells starts coding for the specific proteins required. These amino acids are then put back together in your cells to make the proteins that your body needs. This is protein synthesis.

So, what can we do to maximise muscle protein synthesis?

Factors Affecting Muscle Protein Synthesis

Various factors will increase or decrease the rate at which proteins are made in your cells, and will, therefore, affect how quickly your muscles grow and repair after being damaged during exercise.

Factors affecting muscle protein synthesis *

Conditions or FactorsEffect on Rate of Protein Synthesis
Decreased protein intakedecreased
Increased protein intakeincreased
Decreased energy intakedecreased
Increased cellular hydration (i)increased
Decreased cellular hydrationdecreased
Increased intake of leucine in presence of sufficiency of other amino acidsincreased
Increased intake of glutamine in presence of sufficiency of other amino acidsincreased
Lack of nervous stimulationdecreased
Muscle stretch, or exerciseincreased
Testosterone (and anabolic steroids)increased
Growth hormoneincreased
Insulin-like growth factor one (IGF-I)increased
Normal thyroid hormone (ii)increased
Excess thyroid hormonedecreased
Catecholamines (including synthetic ß-adrenergic agonist such as clenbuterol)increased
Physical trauma or infectiondecreased
(i) Cellular hydration refers to an intracellular state and as such is different from extracellular hydration.

(ii) Thyroid hormone (thyroxine and triiodothyronine) stimulate both protein synthesis and degradation depending on their levels in the body. Not enough or too much can be detrimental to protein synthesis. Higher than normal levels of thyroid hormone leads to the catabolism of protein.

* From Amino Acids and Proteins for the Athlete, the Anabolic Edge, Mauro Di Pasquale, M.D., 2nd Edition in Press.

Leucine and glutamine are essential amino acids in the biosynthesis of protein which is why they help to increased muscle protein synthesis. Intracellular hydration.

Catecholamines are neurotransmitters that have physiological effects as hormones such as dopamine (a ‘feel-good’ chemical messenger that helps reinforce behaviour) and adrenaline (which raises our heart rate is and linked to our innate fight or flight response).

Glucocorticoids are types of steroids which are involved in the metabolism of proteins, fats and carbohydrates and have anti-inflammatory properties.

Importance of Protein Synthesis for Runners

As you can see, there are many factors that we can alter to increase muscle protein synthesis to help preserve, maintain and increase muscle mass. For runners, it is the preservation and maintenance which is important as running can be catabolic (it breaks things down). This is because it burns a lot of calories or uses a lot of energy but results in little to no gain in muscle mass. Whilst running is a stressor, it can be seen as more catabolic than an activity like lifting.

We run for a long period of time so the stressor remains for a long period of time and whilst anabolic hormones are stimulated, stress hormones like cortisol are also elevated when we run at high intensities for a long period of time. Weightlifting provides an even greater stressor on the body than that of running but for a much shorter period of time. This stimulates the release of anabolic hormones which help to build and synthesise muscle.

Running does not cause a stressor of such great resistance to become present so there is an insufficient release of anabolic hormones to compete with the release of adrenaline and cortisol (catabolic hormones), which is why runners need to emphasise protein synthesis to try and maintain muscle.

For runners, I recommend trying to follow some of the steps above in the table. To keep it basic, try and make sure you are always hydrated and be careful when buying amino acid supplements online – make sure they contain no banned substances if you plan on competing at a high level. Also, try to stay away from steroids and glucocorticoids as these can have unwanted side effects as well as being illegal in running at the top end.

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