There are three mechanisms of muscle growth: the tension that is put on the muscle, metabolic stress and muscle damage. They are all regarded as causes for muscle growth, one more than the other.
The stress placed on the muscle, both by the force production and by the stretch of the muscle, is considered essential for muscle growth. And the creation of a ‘mechanical overload’ (= gradually increasing the mechanical tension on muscle fibers) is the most important factor for muscle growth.
Simply explained: you want to progressively overload your muscle tissue, to be able to handle more over time. You need to get progressively stronger: doing more reps, taking more weight or doing more sets.
So progress in your strength and training volume is the primary goal when you want to build muscle mass.
Several studies support the potentially muscle-building role of metabolic stress, developed through exercise.You can imagine ‘metabolic stress’ as the acidification you experience during training at higher repetitions.
Metabolic stress is obtained when a muscle relies on anaerobic glycolysis for its ATP production. This then results in lactate production, which then gives the ‘acidification’.
Although the processes by which muscle fibers increase in volume and the processes by which they are repaired differ greatly, muscle damage is considered by many researchers as one of the stimuli for muscle growth. For example, eccentric training in function of muscle growth is often presented as superior to concentric, because of the greater muscle damage it generates. But this potential added value can be attributed to the greater mechanical stress due to eccentric training compared to concentric.
When muscle damage is avoided during training (for example, by working with the same training program for a longer period of time), current literature indicates that it does not negatively affect muscle and strength building .