Not having a ball while you work your abs? Then try this fun variation of the bicycle crunch. It will not only work your abs and obliques, but since you're holding an exercise ball with your feet you'll work your hamstrings and inner thighs, too. Talk about an effective exercise. I highly recommend wearing sneakers to help you grip the ball.

To learn how to do this ab exercise read more.

• Stand in front of an exercise ball. Lie on your back on a mat or rug with your knees bent, and your feet straddling the ball. Lift your feet off the ground and gently squeeze either side of the ball.
• Bend your elbows and bring your hands behind your head for support.
• Now engage your abs and lift the ball off the ground with your knees bent. Keeping the ball between your feet, slowly draw your right knee in toward your chest and extend your left foot away from you. Twist your torso and cross your left elbow to meet your right knee. Then extend your right leg out, bend your left knee toward your chest and touch your right elbow to your knee.
• Do 20 to 25 reps total, alternating between each side.