Did you know that muscle synthesis occurs (contrary to common belief) during exercise? Yes your muscles enter a state of catabolism (breakdown) during exercise, but at the same time as this your body synthesises protein and muscle too.
Interestingly though, the protein or amino acids ingested during exercise is channeled and expressed as either myofibrillar protein (muscle) or oxidative metabolism (energy), and where the protein goes depends on the type of activity performed. This enables you to trigger sport-specific muscle adaptation, so if you’ve performed resistance work, the protein you ingest goes to the muscle for growth, whereas endurance activity channels the protein to your energy metabolism systems.
So if your goals are to gain more muscle mass then be careful not to perform too many reps, or indeed too many sets/exercises because the consequence may be that your protein is channeled to your energy systems and not the muscle where it is so desperately needed!
Tipton, K, D & Luc van Loon, (2013). Nutritional Coaching Strategy to Modulate Training Efficiency. Sodium Bicarbonate. Karger