The increase in force produced by the muscle after a specific long term training is due to a hypertrophy of the muscle fibres that compose it.
This results in an increase in the cross-sectional area of the muscle. Knowing that the muscle develops between 2. 5 and 4 kg per cm2 of cross-sectional area it is therefore understandable that any improvement in this surface area is accompanied by a gain in strength and of course in muscle volume.
During hypertrophy, the contractile elements thicken and the
extracellular matrix* expands to support and reinforce the development
of the whole. This phenomenon occurs when the stimulus of training is
both sufficient and specific and protein synthesis exceeds protein
degradation.
WHAT FACTORS ARE INVOLVED?
When it comes to training, there are three main factors that can initiate muscle hypertrophy: muscle damage - mechanical strain and metabolic stress.
Muscle damage
Exercise can cause damage to the muscle tissue, which leads to various reactions, such as the involvement of macrophages and lymphocytes to repair the damage. This leads to complex reactions that release growth factors that regulate the proliferation and differentiation of satellite cells** and thus initiate hypertrophy.
Mechanical tension
Mechanical tension caused by contractions and stretching is considered essential for muscle development1-2. It is easy to see that mechanical overload induced by additional loads increases muscle mass, whereas no exercise results in atrophy. Resistance training disrupts the integrity of the muscle and triggers different responses at the molecular and cellular level that can initiate hypertrophy.
Metabolic stress
Numerous studies highlight the importance of exercise-induced metabolic stress3-4. The accumulation of metabolites produced by anaerobic glycolysis for the production of ATP, the phenomena of ischaemia***, the production of free radicals, etc. . . i. e. everything that happens at the metabolic level during and following a bodybuilding session, proves to be a significant element5 in terms of the direct and indirect positive effects on hypertrophy.
REMARK
Do not confuse hypertrophy, which is the increase in the size of the muscle by increasing the cross-section of the fibres, with hyperplasia, which is the increase in the size of the muscle by the multiplication of the cells (myofibrils) that make it up.
