Storing Her Energy
Recognizing that she can unleash a forehand on her opponent, Osaka shuffles her feet into position and then grabs the throat of her racket with her left hand. This seemingly innocuous gesture starts a sequence of motion that will muster her incredible forces and release them into a thunderous shot.
Having both hands on the racket helps create a singular movement of shoulders and hips away from the ball, called a unit turn.
Above, Osaka’s hands begin to separate — her left is heading for the target, her right continues the long arcing path of her racket. This long, looping path gives her more time to store energy, which contributes to her power. The longer swing toward the ball also creates more racket-head speed.
But the time it takes to complete that path may add inconsistency to her shot-making.
Her right hip continues to load energy as she steps away from her racket with her left leg to create a wide, stable base.
The left arm is pointing directly at the ball. This keeps the shoulders closed to the target during the rest of the backswing, preventing any stored power from leaking out before the acceleration of the swing.
The deep knee bend in her right leg is engaging the large muscles of her upper leg.
Her left foot is planted, which in itself creates energy. As Newton’s Third Law explains, if Osaka pushes into the ground, then there must be an equal and opposite force pushing back, called ground reaction force. (Sir Isaac Newton never hit a forehand like this.)
Releasing the Power
This position is called the lock-in position, when the butt of the racket is aimed at the ball. It is Osaka’s last chance to store any energy before releasing the energy in her upper body. By now, she has started to release the lower-body energy and a chain reaction is working its way from the ground up: The hips fire open, followed by the torso, the shoulders, the arm and, finally, the wrist.
All players get to this lock-in position, according to Kovacs, who has a doctorate in physiology and biomechanics. But how efficiently they get there and how much power they can store before reaching it largely determines how fast the shot travels.
Unleashing the Shot
In this part of her swing, Osaka is completely off the ground, meaning all the energy in her lower body is gone. Her arms and racket are accelerating to and through the ball, and she is concentrating on making good contact and adding topspin.
Shots like this one, as much as any part of her game, have landed her in the U.S Open final.