The reality is that people will often tell you that you need to be stretching and performing some form of manual therapy or soft tissue work to the Illiopsoas group. But what they wont tell you is that your Psoas is more than likely weak, and could use some extra focus in training. Drills like the one below along with sled sprints, prowler sprints, deep squats, mountain climber progressions, and single leg work with and without deficits will all recruit the psoas more and ensure they are contributing their fair share at the pelvis and spine.
*With a prisoner hold elevate your knee approximately 30 degrees above the level of your hips
*Hold this position for a count of 10 seconds as you try and rotate the elevate leg outward and then across the body inward.
*Keep the shoulders forward and focus on disassociating the leg from your hips as you move
Since the Psoas muscle has origins up the spine, you will need to get some added knee drive upwards to really turn the muscles to a greater degree. And unless you’re routinely sprinting or squatting below parallel, the other hip flexors will invariably be doing a brunt of the work. The downside here is twofold. First, a lack of dynamic control locally at the spine and poor control of the femur can predispose you to several knee and back injuries over time. Secondly, with this exercise you challenge the Psoas isometrically. A function they need to be able to perform with practically any lower body movement. Moreover, in order for the top leg to elevate there has to be simultaneous and equal leg drive from the stance arriving in full extension. The end result here is teaching the hips to “finish” extension properly which just about anyone could benefit from. Think about trying to lock out your deadlift, or drive your hips straight as you explode off the ground. These acts require full extension, and this drill delivers that for you. Last but not least, you incorporate some hip mobility and anti-rotation work for the core which you can never have enough of. The better apt you are at becoming mobile at the hips and stiffer through the core, according to "The Joint by Joint" Principle of training, the greater your energy transfer and power display will be just about anywhere throughout the body/kinetic chain. Utilize this exercise as a filler in between work sets or as a mobility drill on your off days.