As the modern golf swing has changed, the incidence of knee pain in professional golfers is increasing. For those with previous knee injuries, developing a golf-swing modification that reduces knee loading may be necessary to recover performance after injury. The purpose of this study was to test whether ball position modification reduces knee joint load in a golf swing. Thirteen male professional golfers participated in the study. Golf swings were captured using a three-dimensional motion capture system and two force platforms, with conditions for self-selected ball position and eight additional ball positions. Knee internal rotation and adduction moments were calculated. The length of one golf ball (4.27 cm) backward ball position (closer to the golfer) significantly reduced the peak internal rotation moment of the lead knee (- 13.8%) (p < 0.001) and the length of one golf ball (4.27 cm) away from the target ball position significantly reduced the peak adduction moment of the lead knee (- 11.5%) (p < 0.001) compared with that of the self-selected ball position. Based on these observations, we conclude that the backward ball position modification might be suggested for golfers with anterior cruciate ligament injuries, and the away from the target modification might be suggested for golfers with medial compartment knee osteoarthritis.

• One ball position (4.27 cm) backward with respect to the self-selected ball position (backward-full) reduces the internal rotation moment of the lead knee during golf swing and is a suggested modification for golfers with ACL injuries.

• One ball position (4.27 cm) away from the target with respect to the self-selected ball position (away-full) reduces the adduction moment of the lead knee during the golf swing and is a suggested modification for golfers with medial compartment knee OA;

• The moving the ball position a distance of one ball length away from target also increases an in-out club path and is a suggested modification for golfers particularly with having an out-in club path.