How athletes hit a fastball

1 April 2021

Professor Bruce Abernethy spoke to Nature about the reaction times of athletes.

When batters on the Duke University baseball team step to the plate, the opposing team’s pitcher is no stranger. In the days preceding a game, they will have spent hours in virtual reality (VR), watching a 3D avatar of their opponent throw pitch after pitch at them.

With each virtual pitch, the batters call it as a strike or a ball, a fastball or a curveball. Get it right, and the next simulation cuts out a little earlier; get it wrong, and the simulations extend again. Over time, the theory goes, the players will learn to recognize where the ball is heading as early as possible.

“A major element of sports like baseball and cricket is that they’ve been constructed to live right at the edge of human abilities,” says Greg Appelbaum, a cognitive neuroscientist at Duke University in Durham, North Carolina, who splits his time between medical research and working with the university’s sports teams. “If you can pick up a cue earlier, that gives you more time to make a controlled movement,” he says.

The technology used at Duke was developed by WIN Reality, a software company based in Austin, Texas. The version Duke uses does not allow batters to test themselves physically by swinging at simulated pitches or get precise feedback on their virtual shots. But Appelbaum thinks that even the purely perceptual training that the system provides will give athletes an edge.

The heights that these players’ careers reach will depend on many factors, including stroke mechanics, cardiovascular fitness and strength, and the ability to withstand the mental pressures of competition. But in sports such as baseball, cricket and tennis, where balls move so fast that the time to process their flight is minimal, perceptual skills and anticipation are elemental. If a technology such as VR can improve these even fractionally, the benefits on the field could be substantial.

Bruce Abernethy
Professor Bruce Abernethy

When Bruce Abernethy, a behavioural scientist at The University of Queensland in Brisbane, Australia, began studying high-speed sports in the late 1970s, he encountered an apparent discrepancy between what psychologists said was possible and the reaction times that athletes achieved. “If you did the chronometry,” he says, “it suddenly looked impossible.”

Psychologists said it took at least 250 milliseconds for people to begin moving after seeing a stimulus — and that was if they already knew what to do. If they had to decide what movement to make, reaction times doubled. This seemed simply too slow. In elite baseball, cricket and tennis, the ball regularly travels from the fastest pitchers, bowlers and servers to their opponents in about 400 ms. And to strike that ball, a player must be midway through an exquisitely timed and spatially precise full body motion when it arrives.

“The logical solution”, Abernethy says, “was maybe we hadn’t got the time correct as to when the stimulus onset is.” His hunch was that athletes weren’t merely responding to the ball, but acting on information available before the ball began its journey.

Nowadays, Abernethy says, it’s understood that top competitors use three broad classes of information, of which the flight of the ball is the last.

First, before a play even begins, players assess an opponent’s most likely actions given the state of play and what they know of that opponent’s favoured tactics. These contextual cues enable athletes to begin to prepare for the likeliest potential scenarios.

Next, Abernethy and others have shown that, crucially, players extract invaluable information about where the ball will travel by observing their opponent’s body movements as they prepare to deliver the ball — and that elite players use cues that are imperceptible to novices.

Placing cameras where the batter or receiver stands, researchers filmed cricketers bowling and racket-sport players serving and hitting1. They then played these videos to people with varying degrees of skill and stopped the playback at the moment of ball release or racket contact to ask whether the ball would pitch short or long, and go left or right.

“The probability of making a better than chance judgement was related to skill level,” Abernethy says, “so it seemed we were tapping into something that was important.”

By pausing the videos earlier and earlier, the scientists determined that professionals extract useful information sooner in an opponent’s bowling or serving action than novices do. Then, to uncover exactly which movements were most telling in each phase of action, they blocked out specific body parts in the videos. Abernethy laughs when recalling that, to begin with, he did this by laboriously sticking masking tape directly onto 16-millimetre film.

Cues, it emerged, tend to come first from the trunk, then from progressively more-distal body parts. In tennis, for instance, elbow movement provides the next clue, then, finally, racket motion. “What experts were doing was essentially a very skilled biomechanical analysis,” Abernethy says.

Read the full story in Nature