How to Keep Your Knees Bent in Tennis

One of the most frequent commands tennis players hear from their coaches is, “Bend your knees.” The reason it's important to bend your knees before you hit the ball is to help you generate power with an upward leg push as you hit the ball. Driving your legs upward after you bend them helps increase your racket-head speed. Learning how and when to bend your knees and then push up will help you generate more topspin and power in your shots.

You bend your knees in tennis to generate power, not to get lower to the ball. After you bend your knees, you straighten your legs, pushing upward as you open your hips into your shot. This up-and-down movement creates reactive power, which accelerates your racket, contributing to more powerful shots and more spin on the ball. You bend your knees during groundstrokes, overheads and serves.

Without your knee bend, you won’t be able to generate maximum power and spin, so it’s important to learn how and when to bend them. You’ll bend your knees after you plant your front foot on your final step during groundstrokes. After you run to the ball and plant your foot, you’ll bend your knees and begin opening your hip toward the ball, shifting your weight onto your front leg. As you hit the ball, your hip rotation ends as your front leg straightens, bringing your back foot forward. Coaches often tell students to hit the ball with their legs, not their arms.

When you serve, you start by turning your core backward, bending both knees downward as you toss the ball. To begin your forward movement, “throw” your hip forward, causing your torso to rotate into the all, accelerating your shoulder and then your arm. As you move your hip forward, you will push off the ground, jumping into the air to make contact with the ball. Men tend to do this more than women, who often move their hips backward to generate racket-head speed, according to biomechanics expert Dr. Ben Kibler.

Unbending your knees and pushing up too soon will result in less power, since you’ve exploded too early and don’t have much power left to put into your stroke. Exploding upward too late will also decrease your power. An effective way to practice the timing of the knee bend is to stand at the baseline, facing the fence, and have a partner toss balls to you. Hit a few balls with no knee bend to see what it feels like. Bend your knees and stay down, trying to hit ball gently with no upward leg movement. Practice pushing up at different points during your swing to see which feels the most natural. You can sit in a chair or on a bench and stand as you hit shadow strokes to get a feel for this motion. Another practice technique you can use is to lift your back leg off the ground as you hit balls, shifting all of your weight to your front foot.

Some players, especially those who play primarily on clay, shift their weight to their back foot as they hit the ball. In some instances, they will lift their front foot completely off the ground as they hit. Women also tend to “jackknife” out of their serves, shifting their hips backward and weight onto their back foot, notes Kibler. A quick weight shift backward generates less power than a forward weight shift, but it can help accelerate your racket better if you stand still or move straight up when you hit. Practice this technique to determine if it will help your current strokes.