Kneel on the floor so that your hamstrings rest on your heels. Can you do it?

If the answer is no, you're not alone. Most men can't because their knees are stiff, according to Men's Health Fitness Director BJ Gaddour.

Immobile joints can lead to trouble down the road, increasing your risk of injury and hindering your range of motion in exercises like the squat and lunge, he explains.

Related: The Hip Stretch That Helps You Lift More (Plus, It Feels Really Good)

That's why Gaddour swears by the knee flexion stretch shown in the video above.

"The mobilization clears space within the joint capsule itself," Gaddour says. "It also helps to unglue the tight tissues of the high calf and lower hamstring, both of which intersect behind the knee."

Just 2 to 5 minutes per side instantly increases the suppleness in the joint and reduces aches. Gaddour recommends doing it when you wake up in the morning, or before or after your lower-body workout.

More Men's Health:
-- 30-Minute Insane Interval Workout
-- Leg Day Workout For Guys Who Hate Leg Day
-- The Hip Stretch That Can Also Build Muscle and Burn Fat
-- The J.J. Watt Workout

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