There are 5 primary muscles that flex the hip: psoas major, iliacus (collectively known as iliopsoas), rectus femoris, tensor fascia lata and sartorius. All of these muscles play a different role in hip flexion depending upon the position of the hip, knee and rest of the body during walking, running, jumping etc.
There are also secondary muscles of hip flexion which include psoas minor and the muscles of the groin of which the most notable hip flexor is a muscle called pectineus.
Many of the above-mentioned muscles are commonly injured in sports like hockey, soccer and running. They are stubborn injuries often having a high rate of recurrence and slow healing time.
One thing that has become pretty evident to me over the years is the injured muscle is “speaking up”. It’s been doing all of the work for weaker synergists. Synergists meaning the other muscles that help flex the hip.
As the hip flexors perform different jobs based on position certain muscles in the group can get lazy. This may be based on contributing factors such as movement competency, prior injury, strength, surgeries or fixed postures. Eventually the muscle gets tired, sore and ultimately injured.
As these injuries are usually quite painful that often becomes the focus of a treatment plan. While reducing symptoms are important teasing out the weakest muscle in the group is critical for long term injury resolution.
You can build a comprehensive rehab plan around this weak link which should almost always include single leg stability.
When was the last time you strained a hip flexor?