Hip extensions are the best hamstring exercises especially ones that involve the core, glutes, and calves. The two variations below are both single leg exercises which are more challenging but also more effective. You really have to use your abs and glutes to balance your body so you'll burn more calories while doing them.

Exercise
1 Leg SLDL 1. Start by holding a dumbell in your right hand. 2. Keeping your back straight and your left leg straight bend forward letting your right leg come off the ground and behind you. 3. Bend forward until a comfortable range of motion is reached. 4. Return to the starting position and repeat with the other leg and arm. 5. Alternate back and forth until the desired repetitions are met. Trainer's comments:	Sets Reps Weight/ Resistance Tempo Time
Single Leg Hip Extension on Ball 1. Assume back lying position on floor. Place hands at sides with palms down on floor. 2. Start position: Place one heel on top of Flexaball with knee slightly bent. 3. Raise hips off floor by pressing one heel into ball. 4. Return to start position. 5. To increase difficulty, raise and extend arms above chest. Trainer's comments:	Sets Reps Weight/ Resistance Tempo Time