For the strongest disc golf throws, it’s all in the thumbs

When Zachary Lindsey, a physicist at Berry College in Georgia, decided to run an experiment on how to get the best speed and torque while playing disc golf (aka Frisbee golf), he had no trouble recruiting 24 eager participants keen on finding science-based tips on how to improve their game. Lindsey and his team determined the optimal thumb distance from the center of the disc to increase launch speed and distance, according to a new paper published in the journal AIP Advances.

Disc golf first emerged in the 1960s, but "Steady" Ed Hendrick, inventor of the modern Frisbee, is widely considered the "father" of the sport since it was he who coined and trademarked the name "disc golf" in 1975. He and his son founded their own company to manufacture the equipment used in the game. As of 2023, the Professional Disc Golf Association (PDGA) had over 107,000 registered members worldwide, with players hailing from 40 countries.

A disc golf course typically has either nine or 18 holes or targets, called "baskets." There is a tee position for starting play, and players take turns throwing discs until they catch them in the basket, similar to how golfers work toward sinking a golf ball into a hole. The expected number of throws required of an experienced player to make the basket is considered "par."

There are essentially three different disc types: drivers, mid-rangers, and putters. Driver discs are thin and sharp-edged, designed to reduce drag for long throws; they're typically used for teeing off or other long-distance throws since a strong throw can cover as much as 500 feet. Putter discs, as the name implies, are better for playing close to the basket since they are thicker and thus have higher drag when in flight. Mid-range discs have elements of both drivers and putters, designed for distances of 200–300 feet—i.e., approaching the basket—where players want to optimize range and accuracy.

Despite being around for decades, scientific studies of disc golf are scant. There were a pair of PhD dissertations in 2003 and 2007, respectively, looking into the biomechanics of a basic throw; a 2008 paper on the biomechanics of sidearm throwing of "flying discs" (not specifically related to disc golf); and a 2022 study computationally testing the trajectories of different disc shapes when thrown. Lindsey et al. opted to focus on measuring the effects of thumb position on the launch characteristics of a throw for their experiment.

All in the thumbs

Per the authors, the two most commonly used throwing styles in disc golf are the backhand—in which the disc is pulled across the body from the non-dominant to dominant side before release—and the forehand, in which the disc is "thrown sidearm with the player's dominant hand." Regardless of the throwing style or type of disc, "a comfortable and proper grip is essential" for a strong showing on the course, and there are several different ways of positioning one's fingers.

For instance, a "fan grip" involves spreading one's fingers out near the disc's inner edge while one stacks one's fingers on top of each other near that inner edge for a "stacked grip." Thumb placement is crucial in all of them, the authors note, "because it counterbalances the fingers underneath to secure the disc in the hand" and also affects the torque on the disc during a throw.

The team focused on the backhand throw in their study to investigate how thumb position affects the resulting spin rate (angular speed), launch speed (translational speed), and torque. They opted to use mid-range discs rigged with flight sensors. There were two groups of participants: one with players who were either unrated or had PDGA ratings below 900 and another with highly skilled players with PDGA ratings of 900 or higher.