To effectively elevate your knee, your primary focus should be on activating your core rather than your quadriceps muscles. Squeeze your obliques throughout.
Stand hip-width apart with your hands behind your head. Crunch right and lift your right knee toward your left elbow.
Alternate sides, cycling like a bike. 10-15 reps per side.
Place your hands on your hips and widen your shoulders. Bend right, working your oblique muscles. Repeat left. 10-15 repetitions each.
Stand with your feet shoulder-width apart and hold a weight or medicine ball with both hands in front of your chest.
Turn right and rotate your feet. Return to the center and twist left again. 10-15 reps per side.
Stand with feet hip-width apart and hands on hips. Lift your right knee to your chest while contracting your abs. Lower your left knee and repeat. 10-15 reps per side.
Hands on hips, feet shoulder-width apart. Right knee and left elbow to chest. Restart with left knee and right elbow. Alternate sides. 10-15 repetitions each.