Squats are great strength-training exercises to work your quads, your hamstrings and your glutes. If your knees are hurting, you are probably not following proper form. Try these instructions: Stand with your feet hip-width apart and your abs tight.                       Bend your knees and lower your body into a squat position as if you are sitting back into an imaginary chair. Stop when your knees are at 90 degrees. Make sure you are sticking your buns back, keeping your chest lifted and most importantly keeping your knees above your ankles. Do not let your knees go forward beyond your ankles.                 [pagebreak] You can also do variations on basic squats to continue to challenge both your mind and body. It’s always a good idea to change the intensity of your strength-training exercises from time to time. More from Prevention: Get Slim And Sculpted In 20 minutes   Try using an exercise ball against the wall, pressing your back into the ball to stabilize your back and do wall squats.