KPj, how would you go about strengthening a weak psoas?
You just need to get the knee above the hip with a neutral spine and good posture (watch for lower back rounding and chest caving forward - your torso should be like a pillar and not change position). There are various ways to do this and the approach really depends on the individual but i've got some basic progressions...
Activation: I'll put this in a warm up for those who can barely hold the knee above the hip. Get an aerobic step at a height that, when you put your foot on it, your knee is just about level, or a little below the hips. So, right now you look like you're about to do a step up with your foot on the step. Then just "brace", and lift the knee as high as possible without losing form for 5 seconds, and that's one rep. As a starting point, we'll do 3-5 holds per side before every session after mobilising the hips.
You can't strengthen the muscle(s) if you can't switch it on so, no point looking for resistance initially. I do the above and retest every couple of weeks using the assessment mentioned above. When they can hold the knee up for 15 seconds, I then put them on their back, choke a light band around something (normally a resistance machine in our warm up area), and loop the other side of the band around your foot. We place one hand/forearm under the lower back to force the arch to stay put, and we flex the hips/lift the knee towards the chest against the band. I like to "stick" at the top i.e. hold for a second or 2.
You can do with cables, too, which is shown here with 2 feet at a time, but I prefer to do one at a time initially, http://exrx.net/Articulations/Hip.html#anchor845056
At this point i'll also add the kneeling rock back to the warm up, great example of how to do and not to do it in the following blog by tony gentilcore (this movement also highlights the relevance to hip flexion above 90, squatting, and a maintaining a neutral spine). I love this for teaching people how to "feel" the hip flexors "pull" you into a squat.http://www.tonygentilcore.com/blog/q-a- ... g-part-ii/
When the band is no problem and your hip no longer goes on fire from it, you want to move to your feet. This is where the likes of "high knee walks/skips" bring it all together into an athletic movement (and still during the warm up), and ideally you should be able to squat deeper and better at this point and therefore also using flexion above 90degrees in movement...... Remember the challenge can lie in taking what you can do on the floor and doing it on your feet. It's much easier doing things on the floor. You can nail it on the floor then stand up, move around, and crumble into the same old dysfunction that caused the issues in the first place.
So, at this point, you want to move to your feet. One example is standing with your back to a cable, with a D-handle on the low cable. You loop this round your foot/toes and then flex the hip whilst standing against the resistance of the cable. I don't go crazy with this i.e. i won't give it a 5-3-1 progression or anything. I just want people to be able to get that knee above the hip with good form and with ease.
At this point, i've not seen anything miraculous happen from maintaining a dedicated focus on it and i suspect this because you are now putting the new found function to good use in things like squats and lunges. This is the point where a formerly bad squatter will now be squatting deep with good form and lunging off steps etc, and this is really what the function of flexing above the hip is for (as well as sprinting and jumping.. even kicking....).