The Los Angeles Lakers and the Boston Celtics have one thing in common — other than the fact that they’ve both ruthlessly raided the roster of the Cleveland Cavaliers. They both play “positionless basketball,” a style of play in which every player moves across the court fluidly, playing multiple different positions at once. It’s a style of play that requires immense athleticism, which, as a new study in the Journal of Anthropology of Sport and Physical Education suggests, can be indirectly measured by looking at the length of a player’s arms.
The paper, authored by Tesla Monson, Ph.D., a biological anthropologist who conducted the study at the University of California Berkeley but is now at the University of Zurich, focuses on the link between wingspan and athletic ability. Basketball scouts have long recognized wingspan as an important indicator of athletic potential, but the relationship was never studied in great detail. Monson’s study on the physical attributes of top NBA players shows that wingspan is indeed an important determinant of success: In fact, when she looked at the wingspan-to-height ratios of top players like Lebron James. Kawhi Leonard, Jon Jones, James Harden and Stephen Curry, all but Curry have arm spans that are relatively greater than their height.
“So there is a trend we can see that suggests some kind of genetic correspondence, where really tall people tend to have longer arms,” she tells Inverse.
Kevin Durant had the biggest armspan to height ratio of the top five players in Monson's analysis, but he still fell well within expected biological proporitions
Monson’s study is on a concept used in biological anthropology called “allometry” — the idea that body parts grow at different rates, leading to variations in body rates, leading to variations in body proportions. Previously, it was thought that the relationship between height and arm length was an isometric one” If you are seven feet tall, for example, the law of isometry suggests showed that wingspan will be seven feet long as well — a one-to-one relationship. But Monson’s analysis showed that arm spans tend to be relatively longer than people are tall, which she describes as a “positive allometry”.
To arrive at her conclusion, Monson analyzed the heights of 10,000 individuals, including 2,990 basketball players, 1,284 MMA fighters, and 6,068 recruits for the US Army. In the basketball players and MMA fighers, she looked at the relative advantages afforded by a longer arm span: for instance, she looked how quickly the basketball players were drafted based on those metrics. For the MMA fighters, she investigated the link between wingspan and win-to-loss ratio. In both cases, having a greater arm span predicted athletic success: the MMA fighters with greater wingspans won more fights, and the NBA players with greater wingspans tended to be higher picks in the draft.
With that established, Monson set out to test her second hypothesis: Is it actually unusual to have a wingspan that’s longer than you are tall? This is where the army recruits come in: She used them as a control group to determine whether massive wingspans were unique to these elite athletes or a general characteristic possessed by most humans. Monson was surprised to find that the army recruit data showed positive allometry too, suggesting that, while wingspan confers an advantage in sports, it’s also generally a trait developed over the course over our evolutionary history.
“Because Im a biological anthropologist, I want to put things in the context of evolution of humans and what’s considered normal variation in humans today,” Monson explains. “Our ancestors tended to have really long arms for locomoting through trees. So that’s an evolutionary perspective.”
But as with any biological trait, there will be variations, some advantageous and some not. The world of MMA and the NBA is no exception. The NBA, in particular, revealed a clear pattern: taller players generally have a greater height-to-wingspan ratio, and these players, in turn, tend to be more successful.
On average, Monson noted that the ratio of arm span to height was 1.17. But this proportion was slightly higher for standout NBA players
Although Monson was surprised to find that wingspans of even the tallest players fell well within a normal biological variation, her findings echoed the age-old wisdom of professional basketball scouts: Longer and taller is better. “I’m definitely not surprised,” Carl Berman, a veteran NCAA and international basketball scout, tells Inverse. “These guys with longer wingspans have a huge advantage. You can get in the way of a pass, you can get deflections, generally those guys are better rebounders.”
Though wingspan has always been important, he adds that changes in the way basketball is played in the last five to seven years have made this metric even more important. There has been a change in the “basketball environment” that favors tall, lanky players even more: the rise of “positionless basketball.”
Historically, there have been relatively stable roles assigned to the five players on a basketball court. On one end of the physical spectrum are the guards, which are usually shorter players who can shoot from the outside; on the opposite end are tall, strong centers who are good at getting into the mix and rebounding underneath the basket. But now, NBA teams are looking for players that can play both types of roles. This is where wingspan becomes even more important.
“Nowadays, you have a Kevin Durant-type player who can bring the ball up and do a whole bunch of different stuff,” Berman says. “I know the NBA is looking for, ideally, players than can play multiple positions. And if you’re longer and you’re able to defend multiple positions, you’re more likely to be successful.”
Monson and Berman are adamant that there are always exceptions, like Steph Curry, who falls below the average height-to-wingspan ratio but is still immensely successful. It takes many ingredients to make an NBA superstar, and styles of play will inevitably shift over the years, giving certain players advantages. But positive allometry, given this new style, may be playing an increasingly important role.