Athletes who practice resistance-type exercises have particular protein needs: these can be as high as two to three times the recommendation. But endurance athletes (i.e. a moderate intensity sport over a relatively long period such as running, cycling or swimming) also have specific nutritional needs, particularly high-level athletes who sorely test their muscles!
During a long effort, proteins help provide the energy needed by muscles. During recovery, they allow muscles to rebuild themselves and be ready for the next work-out. During the first hours of exercise, the main energy source is glucose. When these carbohydrates tend to run out (after 2 hours), energy is provided by fat reserves. Proteins are used simultaneously, and they provide 2 to 8% of total energy: protein breakdown is increased.
Consuming proteins before training allows the body to have available free amino acids directly to satisfy its energy needs. This thus makes it possible to limit the mobilization of muscle proteins. The quantity to consume depends on the exercise duration: the longer the training is, the more amino acids are oxidized to provide energy, so more proteins will be needed to compensate. It depends also on the composition of the last meal before the training: the more it is carbohydrate-rich, the more the glycogen reserved will be sufficient, therefore the less there will be necessary to mobilize alternative energy resources.
After exercise, muscles are damaged. The body will regenerate them and rebuild in order to be well prepared for the next training: protein synthesis is increased (it is multiplied by 2 to 5 depending on the volume and the intensity of the exercise) for 24 to 72 hours. Simultaneously, protein breakdown remains high so much that if the person doesn’t increase his protein intake the global protein balance will remain negative.
Consequently, it is recommended for athletes to consume proteins after training (a dose of approximately 20g). On one hand it will increase the blood concentration of essential amino acids, which are amino acids that body cannot synthesize. They must be supply by the diet. These ones have a robust anabolic effect: the muscle protein synthesis will be multiplied by 2 to 3. On the other hand it will increase the insulin blood concentration (even if there is no carbohydrate) and this will strongly reduce the protein breakdown.
Globally, these proteins taken just after training will stimulate the synthesis and reduce muscle protein breakdown: the overall protein balance is positive. This profile is favorable for muscle building, and thus performances improve.
Finally, an intense and prolonged physical exercise is associated with numerous hormonal and biochemical changes within the body. This can have a negative impact on the immune system. In the case of under consumption of protein, the restoration of the immune system will be limited. The person is therefore more inclined to contract an infection.