Hamstring strain is one of the most common sporting injuries, and does unfortunately make you more likely to recurrent strains, but why? The extent of injury is directly related to the size and quality of scar tissue formed. After muscle injury, a variety of fascial tissue's components undergo tissue remodelling which initiates micro and macro changes in the tissue. This tissue change results in greater stiffness of connective tissue, and this is down to the increased content of collagen, titin protein, and extracellular matrix.
Changes in the extracellular matrix is most affected after injury as it is the main site of the inflammatory response. Fascial tissue has an abundance of nerve receptors which detect and respond to mechanical stimulations, and damage to the tissue also impacts the sensory feedback detected by the nerve receptors.
Therefore, increased tissue stiffness and alterations in sensory perception makes recurrent hamstring strains more likely. Rehabilitation should look to address tissue stiffness and sensory perception to reduce the likelihood of further hamstring injury, and return to full fitness.
Kawai, T. et al. Previous hamstring muscle strain injury alters passive tissue stiffness and vibration sense. Journal of Bodywork and Movement Therapies. 27: 573-578.