Tips » Weight Training
Why do muscles grow?
It is a concept called overcompensation. When you have a cut, your body repairs the cut and overcompensates by leaving a scar. When you rub your hands raw, your body repairs the skin and overcompensates with callouses.
When you resistance train, you create microtrauma/damage to your muscle cells. The body overcompensates by increasing the cross-sectional diameter of the muscle cell.