A hip flexor strain refers to a tear within the hip flexor muscles group, the iliopsoas being the most common one involved. Often a hip flexor strain goes hand in hand with an adductor strain in the hip (Tyler, Fukunaga and Gellert, 2014).
The two powerful main hip flexors are iliopsoas (consisting of Iliacus and Psoas Major muscle) and rectus femoris, which is one of the four quadriceps muscles.
This typically occurs when the muscle is explosively and forcibly contracted. This can occur in activities such as sprinting or kicking.
In these activities the hip flexor muscle is particularly vulnerable to tearing when it is working in a stretched position or when required to contract against a load (i.e. kicking a ball).
Treatment is resting in the acute phase; once pain free, a gradual stretching and strengthening programme whilst resting from aggravating activities management of choice.
Tyler T.F., Fukunaga T. and Gellert J., 2014, Rehabilitation of soft tissue injuries of the hip and pelvis, International Journal of Sports Physical Therapy, 9(6), pp: 785-797