This is an excellent exercise that works the total lower body and also the abdominals.  This strengthens and tones the buttocks, hamstrings (muscles behind the upper leg), quadriceps (muscles in front of the upper leg), calves and the abdominals.

• Stand with feet hip-width apart.  Hold a medicine ball in front of you, arms extended at chest height.
• Contract (draw in) abdominals and draw shoulder blades down and together, then take a large step forward with your left foot, bending knees so left knee aligns with ankle and right knee approaches the floor, heel lifted.
• Hold the lunge and rotate your torso, arms still extended, as far as you can to the left without altering hip alignment.
• Rotate back to the front, return to starting position and repeat.
• Do 1 set of 12-15 repetitions, then switch legs and repeat or you can alternate legs during the entire set until you do 12-15 reps on each leg.

Tip:  As you lunge, both legs should be bent as close to 90 degrees as possible. Squeeze your buttocks on the side of your rear leg to stretch hip flexors and really work the gluteus maximus (butt muscle).