The hip flexor complex
This week’s fitness blog is focusing on the muscles of the hip flexor complex.
The hip flexor complex is a large muscle group consisting of the rectus femorus and the iliopsoas. The iliopsoas is itself formed of two further individual muscle groups: the psoas major and the iliacus.
How hip flexors are used
The majority of movements around the hip and the femur require the use of the hip flexor muscles; they are also important muscles when it comes to posture. An example of an exercise requiring hip flexion would be if a personal trainer asked a client to raise their leg in front of their body.
The rectus femoris
As part of the quadriceps group, the rectus femoris originates from the anterior ileac crest at the front of the pelvis and hip bone and inserts on to the tibia. Since it passes over the hip joint, it is involved in hip flexion as well as knee extension. A fitness instructor or sports conditioner will see this used a lot if they work with clients who play football, as it’s commonly the muscle you would use when kicking a ball.
The psoas major and the iliacus
These are smaller muscles involved in hip flexion.
The psoas major originates from the transverse processes of the lumbar vertebrae, a series of five vertebrae within the spine, and inserts on to the lesser trochanter of the femur. The psoas major has a “sister” muscle called the psoas minor but this has very little function and indeed is absent in around 40% of people. As well as the part it plays in hip flexion, the psoas major can also affect trunk lateral flexion, as it is connected to the transverse processes of the vertebrae. This means that it can have a significant effect on posture in a lateral flexion.
The iliacus originates from the anterior ileac fossa, which is the front, smooth part of the hip bone, and again inserts on to the lesser trochanter. As it runs in line with the femur and the hip, it is mainly involved in hip flexion and it doesn’t affect the lateral flexion of the trunk.
The danger of shortened hip flexors
As any personal trainer will know, lifestyles today mean that people are often sitting for long periods, for example at a desk, in a car or in front of the television. When we are seated, our hip flexors are in a shortened state with the muscle origin and insertion relatively close together, which can cause the muscle fibres to tighten. The fall out from this is that when we then stand up, the hip flexor will struggle to go through its full length of motion, so instead it causes flexion. Since our feet are on the floor, it can’t cause hip flexion, so it causes trunk flexion, which in turn causes the pelvis to tilt forward, known as an anterior pelvic tilt.
The result is the hyper extension of the vertebrae, which can give the individual an excessive lordotic curve in the lumbar region of the spine. If this continues over time, the issue can become compounded, the hip flexors will get tighter and tighter, causing a more severe anterior pelvic tilt, which leads to a more severe trunk flexion. The spine will then hyper extend further and the erector spinae muscles in the lower back will get tighter. Furthermore, other back injuries are likely to be compounded if the psoas major is overactive and causing lateral flexion.
The other danger of shortened hip flexors is reciprocal inhibition. If your hip flexors are overactive, then your glutes are underactive and being lengthened, which can lead to underactive muscles and back conditions such as sciatica.
These conditions are very much driven by lifestyle. Even if the person exercises, they may not be putting their hip flexors through the full range of motion needed. It is therefore important that a personal trainer is aware of a client’s lifestyle and that a training programme is devised to counteract the effects of long periods spent seated.