**Should feel in lower back and glutes. Legs do not need to come up super high. Squeeze glutes while lifting. Keep knees slightly bent to keep movement out of hamstrings. **
Lay prone with waist on stability ball. Grasp secure anchor or bar near floor. Feet should be above floor with legs straight.
Holding firmly on anchor, extend legs upward by lifting and straightening leg as high as possible. Lower legs to original position with thighs close to stability ball. Repeat.
Since knee is initially bent significantly, hamstrings are not significantly involved.