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Why protein is important for endurance

Protein intake is associated with big bulging muscles. However, this shouldn't deter endurance athletes from optimising their protein intake because it plays an important role for performance.

Jeukendrup Sports Nutrition Sport Science

Isn't protein just for bodybuilders?

Protein intake is associated with big bulging muscles. Big tubs of protein can be found in stores and can be purchased online and most of those tubs show off the impressive physiques of 110 kg (240lbs) bodybuilders flexing and posing to demonstrate how effective the supplement has been. I have yet to see one of those tubs with a skinny endurance runner as advertisement. From working with cyclists I know that sometimes protein was avoided by these endurance athletes because they did not want the muscle bulk. In a recent review entitled “Beyond muscle hypertrophy: why dietary protein is important for endurance athletes”, Dr Dan Moore from the University of Toronto and colleagues address the role and the importance of protein for endurance athletes.

The goal of training is to improve performance. One workout will result in fatigue and maybe some muscle damage. After the workout, recovery will make sure that performance returns to normal or even better than normal and all damage is repaired. This process is then repeated, new fatigue and damage is inflicted and recovery follows again and this process is repeated over and over again. A well planned training program results in improvements in performance, greater resistance to fatigue and more rapid recovery.

So why is protein important for endurance athletes?

Prolonged endurance training sessions cause large changes within the muscle; fuel stores are depleted and certain metabolites accumulate (metabolites are often referred to as waste products, but this a misnomer as they are not always “waste”). Protein structures in the muscle get damaged and need removing, repairing or replacing. This is where nutrition comes in. Carbohydrate and to some extent fats are needed to replenish fuel stores. Protein nutrition is needed to repair or replace protein structures. Therefore increasing nutrient availability (carbohydrate and protein) immediately post exercise is often recommended to facilitate replenishing and remodelling of the muscle. When protein is ingested it is broken down to its smallest units called amino acids. These amino acids will then be absorbed and transported to the muscle. In the muscle these amino acids will form the building blocks for new proteins.

Protein nutrition is needed to repair or replace protein structures.

Following weights training the amino acids from nutrition will be used mainly to rebuild contractile proteins and over time this will add up to greater muscle mass: larger bulging muscles. Weight training causes various molecular changes in the muscle that will direct amino acids towards building bigger muscles.

What changes happen in the muscle after endurance exercise?

With endurance exercise the changes in the muscle are different and at the end of an endurance workout the environment within the muscle is quite dissimilar to that after weights training. After endurance exercise, there are large “stress signals” that can actually prevent the building of bigger muscle. Instead these signals will activate different processes that will direct amino acids to make different proteins. Instead of building contractile proteins (the proteins that make up muscle fibers), the proteins that are preferentially built are so called mitochondrial proteins. Mitochondria surround contractile proteins and serve as the power plants of the muscle. This is the place where the final stage of carbohydrate and fat breakdown takes place to provide energy for muscle contraction and thus these proteins are extremely important for endurance athletes. In fact endurance athletes have many more of these mitochondrial proteins than weight trained athletes. Protein in the diet and especially protein immediately after a workout are most likely required to optimize these processes.

What is optimal?

How much, when and what type of protein would work best for endurance sports is still to be determined but studies so far have suggested that a protein intake of 20 grams after exercise and at regular intervals thereafter would be best (every 2-3h). The protein source should be rapidly digested and be relatively high in the amino acid leucine. There are many different types of protein that could do this but whey protein seems to be a very effective protein source, which has been shown to be more effective than soy protein, which in turn has been shown to be more effective than casein (a slowly digested protein) (proteins types and terminology). Some studies have also shown that carbohydrate ingestion with the protein will not only help recovery by restoring body carbohydrate stores but also help the building of new proteins.

Studies so far have suggested that a protein intake of 20 grams after exercise and at regular intervals thereafter is best (every 2-3h).

Dr Moore and colleagues conclude that although we still have a lot to learn about the best protein intake strategies for endurance athletes, it is clear that protein intake plays an important role in optimizing the long term benefits of training. They also conclude that protein is a vital and often underappreciated component of the endurance athletes’ nutritional armour.


Moore DR, Camera DM, Areta JL, Hawley JA. Beyond muscle hypertrophy: why dietary protein is important for endurance athletes. Appl Physiol Nutr Metab. 2014 Sep;39(9):987-97.


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