DEEP HIP FLEXOR TRAINING
Hip Flexor tightness has been a common theme with many of the athletes I have screened over the years and these muscles often get the blame for hip and lower back pain. In my experience, the more superficial hip flexors (TFL, Rectus Femoris, Sartorius) are the muscles that often become dominant and shorten, sometimes influencing issues with the lower back, pelvis and hip.
The opposite seems to happen with the deeper stabilizing muscles (Pectineus, Iliacus and Psoas- although Psoas is arguably not a true hip flexor, just active during hip flexion). These often get neglected and can become elongated and inefficient at controlling hip and lower back motion. It is therefore beneficial to improve their function to help protect the hip and lower back from injury.
It can be a challenge to find an exercise that allows you to activate the deeper hip flexors without involving the often dominant superficial ones. However, I find the side plank with hip flexion a useful exercise that enables the deeper hip flexors to become more dominant during hip flexion. You also get some really good activation of the internal oblique and opposite hip adductors - important in protecting the lower back too.
When I teach the exercise I try to ensure that the trunk is straight and the top hip and lower back are kept in a neutral position to ensure hip flexion with the bottom hip is the only movement occurring.
Before performing this exercise, please check with a medical or fitness professional to see if it is suitable for you - especially if you are suffering from any hip or lower back issues.