28/08/2026
Most hip flexor stretches leave the actual culprit completely slack.
Re**us femoris is the only one of your quads that crosses the hip. It bends the hip and it straightens the knee, so it's working across two joints rather than one.
That's exactly why the standard kneeling lunge misses it. With your back shin flat on the floor and that knee close to straight, re**us femoris has plenty of slack at the bottom end, so you can hold the position for months and never actually lengthen it.
It's also the most likely one to be short if you're active, because it's involved every time you lift a knee and every time you straighten one. Running, cycling, squatting and kicking all load it, and then you sit on it for eight hours in between.
There's a quick way to tell. Do your usual lunge stretch and note what you feel, then bring that back heel up towards your backside. If it suddenly bites hard down the front of the thigh, you've just found the muscle you've been missing.
The two also feel different. Psoas sits deep in the crease of the hip, re**us femoris runs down the front of the thigh.
That's what the couch stretch solves, because the foot up behind you puts both ends on stretch at the same time. Squeeze the glutes as you settle in so the range comes out of your hip rather than your lower back, and give it three sets of 30 seconds most days.