Can you bring your knee to your chest without rounding your back? A lot of guys can’t.

That’s the result of a weak psoas, the muscle that connects your lower back to the top of your thigh and is responsible for lifting your knee above hip level, says Men’s Health Fitness Director BJ Gaddour, C.S.C.S.

And it’s a problem, because the weakness limits how deep you can squat and lunge, and even screws up your running technique, ultimately hindering your overall performance, Gaddour says.

In the video below, Gaddour demonstrates three drills that will strengthen your psoas. Perform 5 to 10 reps on each side of each movement as a warmup or activation drill, or plug them into a circuit.

“Strengthening this area will unlock your performance, improve your range of motion, and make you a beast,” Gaddour says.