Flat ground is fine. Then you take the stairs and there is a sharp pinch at the front of the hip, right in the crease.
Pinching in the front of the hip when you flex it is a mechanical event, not an inflammation.
The head of the femur is not centered in the socket, so at the top of the range something makes contact that should not. Two things usually cause it.
The glutes are not controlling the femur
The deep hip muscles are supposed to hold the joint centered while you flex it. Sitting all day means those muscles rarely work at all, and unused muscles stop being recruited. So when you load one leg on a stair, the femur drifts forward and jams.
The pelvis has nowhere to go
Stair climbing needs the pelvis to rotate slightly. If your mid-back and ribs are stiff, that rotation gets blocked upstream and the hip has to find the range on its own, at the end of its available motion. That is where the pinch lives.
What I test
Passive hip flexion with you on your back, watching when the pelvis starts to move. Hip internal rotation, both sides. Then single-leg stance and a step-up, to see whether the femur stays centered when you actually load it.
“He resolved a chronic lower back issue I had been dealing with for years, improved my glute strength, and got me back to training at full intensity in just a few months.”
What we do
Get the joint centered, usually with breathing and specific positional work before anything gets loaded. Then teach the glutes to control the femur through flexion. Then load the step-up pattern properly, which is also the pattern you use every day.
A client came to me with a pinch on the stairs and a hip that felt tight all the time. It was not tight. It was uncontrolled. Once the deep hip muscles started doing their job the pinch stopped, and no amount of stretching had ever touched it.