Here's a terrific way to train your hamstrings (the muscles in the back of your thighs) and buttocks without overworking the fronts of your thighs. It's excellent for people who have sensitive knees and cannot perform squats or lunges.
Begin on all fours on a padded, level surface. Place your elbows on the floor under your shoulders, palms facing down. Balance on your right knee, making sure it's directly below your right hip. Now straighten your left leg behind you and raise it up to hip level. Press out through your left heel and flex your foot. Keep your abdominals pulled in toward your spine and avoid over-arching your lower back.