Strengthening your knees for pickleball involves targeting the muscles around the knee joint to provide support and stability. Strong knee muscles can help prevent injuries and improve overall performance on the court. Here are some exercises to help strengthen your knees:

1. Quad Sets: Sit with your legs straight out in front of you. Tighten the muscles on the front of your thigh (quadriceps) and press the back of your knee into the floor. Hold for a few seconds and release. Repeat for multiple sets.
2. Hamstring Curls: Stand behind a chair or use a wall for support. Bend one knee and bring your heel toward your buttocks. Hold for a moment, then lower your leg back down. Repeat on each leg for several repetitions.
3. Wall Squats: Stand with your back against a wall and your feet shoulder-width apart. Slowly slide down the wall into a squatting position, keeping your knees directly above your ankles. Hold for a few seconds and then return to the starting position. Repeat for multiple sets.
4. Step-ups: Use a sturdy step or platform. Step one foot onto the platform and push through your heel to lift your body up. Step back down and repeat on the other leg. Perform several repetitions on each leg.
5. Lateral Band Walks: Place a resistance band around your ankles. Take small steps to the side, maintaining tension in the band. Walk in one direction for several steps, then return in the opposite direction.
6. Calf Raises: Stand with your feet shoulder-width apart. Rise up onto your toes and then lower back down. Repeat for multiple sets.
7. Single-leg Balance: Stand on one leg and hold the position for as long as you can without wobbling. Switch to the other leg and repeat.
8. Bicycle Exercise: Lie on your back with your hands behind your head. Bring one knee towards your chest while simultaneously rotating your torso to bring the opposite elbow towards the knee. Repeat on the other side, mimicking a cycling motion.
9. Glute Bridges: Lie on your back with your knees bent and feet flat on the floor. Lift your hips off the ground, squeezing your glutes and core. Hold for a moment and then lower back down.
10. Prone Leg Lifts: Lie on your stomach and lift one leg off the ground while keeping it straight. Hold for a few seconds and then lower it back down. Repeat on the other leg.

Remember to start with a proper warm-up before engaging in these exercises and stop if you experience any pain or discomfort. It’s always a good idea to consult with a healthcare professional or a certified fitness trainer before starting a new exercise program, especially if you have any pre-existing knee conditions or concerns.