Fig. 3.

Schematic draws of trapezius muscle during each swing phase. Trapezius muscle thickness is increased in the lower cervical and upper thoracic region (A). During back swing, right upper and middle trapezius muscle contract from address-neutral state (B and C). During forward swing, the left middle trapezius muscle contracts (D). The force may amplify during the acceleration phase (E). When a right-handed golfer swings such that the club contacts the ground before the ball back swing arc energy cannot be transmitted to the ball (F).