In short, the Force Factor is the maximum torque produced in the swing normalized by body mass, meaning the maximum torque is divided by body mass (in kilograms) to allow for even comparisons between golfers.
Generally, a golfer with a greater body mass will produce larger forces than a golfer with a lesser body mass, simply due to the added mass (since force is the product of mass and acceleration). By removing this effect, the Force Factor indicates the degree to which the golfer is able to produce torque from his or her available body mass. In other words, it is a measure of how well the golfer utilizes his or her potential to produce torque. Our preliminary data from PGA Tour players show that an increase in Force Factor tends to coincide with an increase in the rate of torque development (figure 1), which is a measure of how fast the golfer is able to increase torque. This relationship implies that the Force Factor can be used as an indicator of a golfer's explosiveness. Further, our data show that the rate of torque development is positively related to clubhead speed (figure 2), pointing to the importance of explosiveness in the golf swing.
Figure 1: The correlation between rate of torque development (Nm/s) and Force Factor shows that the greater the Force Factor is, the more explosive the torque production tends to be. (click on image for larger version)
While several factors affect clubhead speed, the maximum torque produced remains fundamental (for details, see our article on force transfer). The Force Factor provides a notion of the golfer's potential for producing this torque, allowing for the assessment of arguably one of the most critical factors for swing performance. For instance, if a heavier golfer produces a Force Factor of 1.10 while a lighter golfer produces a Force Factor of 1.30 with the same club, it indicates that the heavier golfer might be relying more on brute force than technique compared to the lighter golfer. As such, all things being equal, the heavier golfer should have the potential to produce greater torque by improving his or her technique, given the advantage in body mass. On the other side of the comparison, being able to produce relatively greater torque despite a disadvantage in body mass means that the lighter golfer has greater relative strength, which is important for explosiveness.
Figure 2: The correlation between rate of torque development (Nm/s) and clubhead speed (mph) shows that the more explosive the torque production is, the greater clubhead speed is generally achieved. (click on image for larger version)
Dr. David McGhie (Swing Catalyst Head of R&D)