The measurement of upper body alignment during the golf drive.

Transverse plane rotations of the upper body are often estimated during the golf swing. The aim of this study was to determine the agreement between upper body alignments measured using markers attached to the thorax and markers on the acromion process during the golf drive. Three-dimensional coordinate data from nine markers were collected (300 Hz) during eight golf drives for 10 participants. The transverse plane alignment of the upper body was calculated using three techniques: inter-acromion vector, thorax vector, and Cardan angles. Agreement between the methods was then assessed using intra-class correlation and 95% limits of agreement. Our results suggested that the thorax vector can be used to provide an accurate estimation of thorax alignment at all stages of the golf swing (R > or = 0.97, systematic difference < 1.0 degrees , random difference < 3.8 degrees ). The inter-acromion vector gave an accurate estimation of thorax alignment at address (R = 0.90, systematic difference = 0.0 degrees , random difference = 4.3 degrees ) but it should not be used to estimate thorax alignment at the top of the backswing (R = 0.32, systematic difference = -16.0 degrees , random difference = 8.7 degrees ) or impact (R = 0.90, systematic difference = -5.1 degrees , random difference = 8.3 degrees ) during the golf drive.