"Muscles need to fire at a specific sequence and a specific time to produce the most force. All of our muscles wrap around the body, very few are in straight lines, and in this regard they need to be trained appropriately," says MacMillan. With knees bent and butt a couple inches from the floor, lean your back against an exercise ball. Hold 3-pound weights in each hand at chest level, palms facing upward. Extend your arms straight behind you and your legs at the same time, rolling backward over the ball. Arms should remain parallel with the floor. Reset to starting position, and then repeat.