Muscle cells work by contracting (pulling) and relaxing only, nerve activation of the cell triggers 2 layers called actin and myosin to slide over one another. Damage to skeletal muscle through intense exercise can either result in muscle growth or injury depending on the circumstances.
Intense exercise will cause microscopic tears between cells that the body responds to by promoting the growth of additional muscle cells. If the tears are too large cells may rupture and undergo a process or apoptosis, or programmed cell death. If cells rupture, the internal parts of the cells are released into the spaces between cells triggering an immune response. Macrophage cells from the body’s immune system will migrate to the site of damage and clean up the mess.