Adding a leg lift to your side plank tones the outer thigh while challenging your core. The trick to keeping the pelvis high as you lift your top leg is to reach the inner thigh of your bottom leg toward the ceiling.
Place your right elbow on the ground. Extend both legs out so that your body is in one straight line and you're balancing on the outside edge of your right foot. Flex both feet if you can, and rest your left hand on your upper hip.
Keeping your spine lengthened and your abs engaged, lift your left leg up just higher than your top hip. Then slowly lower it back to your bottom leg.
Keep your waist up and lifted, and don't sink into your bottom shoulder.
Do three sets of 15 to 20 repetitions on each side.