This  month's entry is the Russian Twist. Besides helping you develop rotational strength, the constant load on your glutes makes it a great lower body strengthener as well. To begin, hold a medicine ball (or light dumbbell) between your hands and lie back on a stability ball. Extend your arms until the ball is right above your chest, and bridge your glutes so that your legs are bent 90 degrees. Next, brace your core and keep your arms straight as you turn to one side, making sure to allow the ball to roll slightly beneath you. When your arms are parallel to the floor and you're balancing on one shoulder, pause for a second and then bring the ball back up to the starting position, and then repeat to the other side.

Be sure to keep your core and glutes braced throughout the movement to avoid unnecessary strain on the lower back. Also, try to focus on using your torso, rather than your arms, to bring the ball back up to the starting position. Begin with a light ball to get the form down and then once you've become comfortable with the movement, pick a weight that challenges you for 12-16 reps (6-8 reps per side).