Lie with back on ground and heels on physioball
Raise body off ground so that only upper back touches floor
Keeping body straight, roll ball towards you by pulling heels to butt
Slowly straighten legs and repeat
Sets/Reps: 3x8; work up to 15 reps, then perform advanced variation
Advanced: One leg at a time
Problem Solved: Weak or frequently strained hamstrings
Peacock: Most people are flexible enough in their hamstrings, because they were taught to reach down and touch their toes when they were little. But you also need to work them functionally, with your glutes and low back.