Knee flexion prone with stability ball

Flex the knee by drawing the heel in the required direction, then control the return. Keep the pelvis from shifting to create extra range. Use a steady tempo: control the return phase in particular and avoid relying on momentum. Exhale through the hardest part and inhale as you recover the starting position.

Check that the movement stays stable in both directions and that the torso is not compensating. The goal is controlled loading of hamstrings; match resistance and range to a beginner level and never force a painful repetition. On unstable surfaces, master the position with light resistance first; stability should limit difficulty before load does.