Ever feel that weird pinching in the front of your hips when doing feet-hooked situps? That’s just your hip flexors saying hi. This group of 12 muscles—which includes the psoas, iliacus, and sartorius—helps you raise your thighs up (or in the case of those situps, helps you raise your chest toward your thighs). The muscles also tend to get overused and shorten from sitting too much.

And while your hip flexors are comparatively small muscles—rare is the bodybuilder who focuses on his psoas—they are absolutely essential for a range of athletic movements, from running to jumping to even heavy back squats.

“Tightness in the hip flexors—rather than strength—is what’s generally most concerning,” says Rachel Straub, M.S., C.S.C.S., an exercise physiologist and author of Weight Training Without Injury. “Hip flexor tightness tilts the pelvis permanently forward, a condition known as lumbar lordosis, which causes biomechanical problems and even pain at both the knee and low back.”

To loosen up your hip flexors, you’ll need to add some targeted stretching to your routine—and nix any exercise, like feet-hooked situps, that overworks your hip flexors. Do these stretches dynamically (with movement) before your workouts, and statically—by holding still—at the end.

3 exercises to strengthen and mobilize hip flexors:

1. Double-Leg Curl
Lie face down on your stomach. With feet flexed, bend your knees so your heels come toward your butt. As a warmup, hold for a beat, then release, doing 30 reps. As a cooldown stretch, hold the curl for 30 seconds. Rest for a moment, then do two more sets. “This exercise stretches the hip flexors that cross the knee joint,” says Straub.

2. Supine Gravity Stretch
Lie on a bed, high bench, or massage table on your back, with your legs hanging off the edge of the surface. Pull one knee in toward your chest, holding it with your hands, while you let the other leg hang down, knee soft, foot toward the floor. As a dynamic warmup, hold for two seconds, then switch legs, going for 15 sets. As a static stretch, hold for 30 seconds on each side. Rest do two more sets. 

3. Lunges
Kneel on a mat. Step one foot forward, as far as you can while maintaining a right angle in the front leg with the back leg fully extended behind you, thigh as close to parallel to the floor as you can make it. Hold for 10 seconds then switch as part of your warmup; hold for 30 seconds on each side as a cooldown stretch. “This exercise should be avoided until the first two hip flexor stretches can be done with ease, as it can exacerbate both low back and knee pain,” Straub says.