With your back against a wall, hold a medicine ball with both hands in front of your chest and lower into a squat (a). Keeping your hips steady, twist to the left and reach the ball toward the wall (b). Return to centre. That's one rep. Repeat on the other side. Move back and forth at a slow, controlled pace for 20 total reps. Quick tip: Make it harder by fully extending your arms instead of bending your elbows.