Step by step instructions
Lie on right side, with right elbow bent under shoulder, lifting ribcage away from the floor with hips stacked and knees bent at 90 degrees in front of hips. Extend top leg straight in front of hip, foot flexed.
Bend knee into chest, then press out through heel to extend leg straight (imagine pushing something away from body with heel). Do all reps on the right side, and then repeat on opposite side to complete the set.