When we exercise, this puts a stress on the body which is ultimately beneficial because it causes our body to adapt to this stress. As we repeatedly exercise over time our bodies undergo physical changes which help our bodies tolerate the stress caused by exercise. One of these adaptations is a growth in muscle size. 

Most of us have heard that resistance training like weight training can make our muscles bigger but not many of us really understand why. The physiological process whereby muscle tissue grows in size through increased protein synthesis is called hypertrophy, and it plays a crucial role in the health, growth and athleticism of all human beings. There are three major theories about how hypertrophy occurs, although these theories are not seen as mutually exclusive so the real question is which theory describes the dominant mechanism of hypertrophy. 

Most of us have heard that resistance training can make our muscles bigger, but not many of us really understand how or why. Image Credit: Trainer Academy

Mechanical Tension is thought by most researchers to be the most dominant mechanism. When the human body partakes in resistance training the weights used in the training session subject the body to mechanical tension. This mechanical tension disrupts the integrity of the muscle which stimulates cell signalling responses which encourage protein synthesis. 

Muscle Damage is another theory of how hypertrophy occurs. This theory states that during training your muscles are damaged and during the recovery process they are healed in such a way that they become bigger and stronger. Muscle Damage is the major cause of soreness in your muscles after a training session. 

The final major theory of hypertrophy is Metabolic Stress, which hypotheses that the increased blood flow to muscles as a result of their repeated contraction and relaxation during training is responsible for the build-up of metabolites which then leads to changes in cell signalling which stimulate muscle growth.

Cover image credit: Total Shape

Richeal Ni Laoghaire – Former Science Editor