Takagi T, Murata M, Yokozawa T, Shiraki H. Dynamics of pelvis rotation about its longitudinal axis during the golf swing. Sports Biomechanics, 2019, April 30: 1-20.

The purpose of this article was to investigate the kinetics that produce the transverse plane rotation of the pelvis during a golf swing. Specifically, the rotation that occurs during the back swing and downswing prior to impact was analyzed using a mathematical process called “induced acceleration analysis.” The swings (with a driver) of 31 low handicap golfers (both men and women) were measured using high-speed motion capture and force plates. Of particular interest to the researchers were the internal joint torques and the timing of the torques at different phases of the back swing and downswing. 

The results related to the timing of the torques in the trail (back) hip might be the most important to movement specialists. They found that the peak torques in the back hip and the front (target) leg occurred generally around the same tame with one exception. The authors note that during the initiation of the downswing, the frontal plane abduction torque of the back hip preceded the peaks of the other torques. Reading the article, one could argue that the other torques did not occur at the same time, but there is no doubt that the abduction torque peaked first. 

So what would be the practical consequence of this frontal plane motion? Well, it appears to be consistent with a well-accepted shift of the body weight from the trail leg to the target leg prior to (and in order to maximize) the aggressive rotation of the pelvis towards the target. Consistent with other research, the rotational velocity of the pelvis peaks before ball impact. The authors note in their review of the literature that many research articles have identified differences in the rotation of the pelvis between genders, age, and skill levels of golfers. From an Applied Functional Science® (AFS) standpoint, the questions become: Is this frontal plane torque a “truth” of the golf swing? If it is a “truth” in golf, is it found in other functional activities? Can the biomechanical Chain Reaction® be trained?

In golf, the transfer of weight to the front leg has been proposed to create a “post” (axis) around which the pelvis, trunk, arms, and club rotate to generate club head speed. In baseball pitching, cricket bowling, and javelin throwing, there is a similar “posting” of the front leg in order to maximize the velocity at which the implement is released. So there are kinetic similarities in other sports. From the Gray Institute® perspective, this sequencing of torques and creating an axis for maximizing rotational velocity is a “truth” of all efficient movement. In AFS, this axis is not fixed, but changes during the movement. Therefore it is called a “functional axis of motion.”

To understand this functional axis at a deeper level, let’s return to the golf swing. The longitudinal axis referred to in the article is a vertical axis around which motion in the transverse plane occurs. If this axis is fixed in the center of the pelvis, then the rotation of the pelvis during the back swing and downswing would be similar to turning the steering wheel on a car. With the axis fixed, the right side of the wheel moves up or down the same distance (but opposite) the left side of the wheel. If this were true of the golf swing, then during the backswing for a right-handed golfer, the left side of the pelvis would move forward the exact same amount as the right side would move back. Although this can occur, more often the target side of the pelvis moves forward more than the trail side of the pelvis moves back. During the downswing, the opposite is often observed. When this happens, the axis of rotation can’t be fixed in the center. It becomes a shifting functional axis that moves based, in part, on which leg is bearing a greater percentage of the body weight.

Could this be the why the frontal plane abduction torque precedes the rotational velocity? Could this shift of the functional axis towards the target leg be reduced if there is not enough lead leg strength? Could differences in weight shift produce the different rotational patterns of the pelvis in different genders, ages, and skill levels? If this a “truth” or principle of human movement, can practitioners create training movements to improve function that are specific to the sport or activity? That final question is the driving force behind Gray Institute®. Gray Institute® strives to understand the Principles of human movement, to investigate the Chain Reaction® Biomechanics of any activity, and to teach movement professionals how to “create and manage” individualized training programs to “facilitate the desired Chain Reaction function.”