A muscle-tendon unit can be injured when it is either passively stretched or stretched while activated. In eccentric exercise, the contracting muscle is forcibly lengthened; in concentric exercise it shortens. While concentric contractions initiate movements, eccentric contractions slow or stop them. A strain injury frequently occurs in the setting of eccentric contraction. Forces generated within eccentrically activated muscle are higher than in a concentrically activated muscle, thus increasing susceptibility to injury. 
Three phases have been identified in this process:
Destruction phase, characterised by the rupture and ensuing necrosis of the myofibres, formation of a haematoma between the ruptured muscle stumps, and inflammatory cell reaction.
Repair phase, consisting of the phagocytosis of the necrotised tissue, regeneration of the myofibres, and concomitant production of a connective tissue scar, as well as capillary ingrowth into the injured area.
Remodelling phase, a period during which regenerated myofibres mature, the scar tissue contracts and is re-organised, and the functional capacity of the muscle recovers.
There is no specific pathophysiology for ligament sprains, as they are a static structure.