what is muscle hypertrophy?

The term ‘Muscle Hypertrophy’ relates to an increment in muscle mass. It occurs as the result of muscle/strength training by weightlifting. It is the primary goal of athletes to increase muscle mass. Though it can be achieved through various methods of resistance training programs by following the basic principles and following the routines can promote greater hypotrophy than other methods. Bodybuilders usually train with moderate loads and have short intervals which will induce a high amount of metabolic stress. On the other hand, powerlifters routinely train themselves with high loads with longer rest periods between their sets. Yet it is still not clear which is the best method to maximize muscle hypertrophy.

• Satellite cells and muscle hypertrophy

Muscle which a postmitotic tissue that will not undergo significant cell replacement throughout life there a method for cell repair is required to avoid apoptosis and maintain skeletal mass. The previous research shows that hypertrophy is mediated by satellite cell activity. These cells reside between the basal lamina and sarcolemma.  Induced satellite cells proliferate and fuse to existing cells to create new myofibers, that provide the precursors which are needed for repair and subsequent growth of new muscle tissue.

• Myogenic Pathways

Hypertrophy induced via exercise is facilitated by various signaling pathways, several anabolic signaling pathways have been identified which include Akt/ mammalian target of rapamycin(mTOR), calcium(Ca²⁺) dependent pathways, and mitogen-activated protein kinase (MAPK) pathway.

• Akt/Mammalian Target of Rapamycin Pathway

The Akt/mTOR is found to act as a master network for regulating skeletal muscle growth. The pathway on activation, Akt signals mTOR to promote hypertrophy in muscle tissue.

• Mitogen-Activated Protein-Kinase pathway

The mitogen-activated pathway is considered as the regulator of gene expression, metabolism, and redox status. MAPK has been shown to link the cellular stress in myocytes with an adaptive response. Three signaling molecules are associated with exercise-induced muscle-hypertrophy:

• An extracellular signal-regulated kinase(ERK 1/2).
• p38 MAPK
• c-Jun NH2-terminal kinase
• Calcium-Dependent pathways

Several Ca²⁺ dependent pathways have been associated with the regulation of muscle-hypertrophy. E.g., Calcineurin(Cn) which is a Ca2+ regulated phosphatase

• Factor affecting muscle hypertrophy

Numerous factors affect muscle hypertrophy some of them includes:

Hormones and cytokinins, insulin-like growth factors, testosterone, Growth hormone, hypoxia.

• What is transient hypertrophy?

The hypertrophy which is obtained when an individual is performing any single exercise is known as transient hypertrophy. This increase in muscle size is due to the effect of fluid accumulation, from blood plasma in the intracellular spaces of the muscle.

• What is chronic hypertrophy?

The hypertrophy which is obtained from long-training resistance training is known as chronic hypertrophy. It changes both the number of muscle fiber(fiber hyperplasia) and the size of the muscle fiber( fiber hypertrophy)

• Difference between transient and muscle hypertrophy

S.NO	Transient hypertrophy	Chronic hypertrophy
1)	Obtained via a single exercise	Obtained via long-term training
2)	Short term Changes in muscle size	Change in both muscle fiber number and size
3)	Can be obtained by short-term/single exercise	Only obtained from long-term resistance training
4)	Results can be observed during the resistance training	Results can be obtained and observed that may vary according to time and type of training