This exercise targets the muscles of your glutes and hamstrings, which are key for a healthy back and stable knees.
How to do it: Place a band around both legs just below your knees. Lie on your side with your hips and knees bent 45 degrees, legs stacked. Keeping your feet in contact with each other, raise your upper knee as high as you can without moving your pelvis. Don't allow your lower leg to move off the floor. Pause, then return to the starting position. Do 20 reps on one side and then repeat with the other leg on top.