Your knees and ankles are the key to jumping higher, according to a new study in the Journal of Strength and Conditioning Research.

A vertical jump involves “triple extension”—fully extending the ankles, knees, and hips. Even though all three joints are involved, the faster and more forcefully you can contract the muscles surrounding your ankles and knees as you extend, the higher you’ll jump, found the researchers.

Your hips play a bigger role when you jump forward, not up.

While strength is important in your ankle and knee muscles, it will only propel you so high. You need to concentrate on improving their rate of contraction if you want to add inches to your vertical, says study co-author Marc Norcross, Ph.D.

Do this by adding the following two exercises to your workout routine.

 Weight-Release Jump

Grab a pair of light dumbbells and hold them by your sides, palms facing each other. Dip your knees, and then explosively jump as high as you can. As you leave the floor, release the dumbbells from your hands. That’s 1 rep. Perform 3 to 5 reps in a row with maximum intensity.

Depth Jump

Stand on the edge of a 30cm high box or bench. Step off, landing softly on the balls of your feet followed by your heels. Both feet should hit the floor at the same time. When you make contact, bend your knees slightly, and then explode as high as you can. That’s 1 rep. Do 3 to 5 sets of 8 reps.