Leonardo da Vinci's
Vitruvian Man—the famous depiction of a man's body inscribed in a circle and a square—is accompanied by text indicating the ideal proportions of the human body. "The length of a man's outspread arms," the translated caption declares, "is equal to his height." Had Da Vinci been born about five centuries later and worked in an NBA front office instead of a Renaissance workshop, there's no way his Vitruvian Man would fit in a square.
Most people do indeed have a wingspan approximately equal to their height. But an analysis of measurements from NBA predraft combines—where players are measured without shoes—for my forthcoming book The Sports Gene shows that the average ratio of arms to height in the NBA is an astounding 1.06. (To put that in context, a ratio of greater than 1.05 is one of the diagnostic criteria for Marfan syndrome, a disorder of the body's connective tissues that often results in elongated limbs.) Thus, an average NBA player, who stands about 6'7", has a wingspan of seven feet.
Certainly it doesn't take statistical analysis to conclude that NBA players are freakishly tall. (Although some stats help put the freakishness into perspective: Seven-footers are routine in the NBA but so rare in the rest of the country that of American men ages 20 to 40 who stand seven feet tall, an estimated 17% are in the NBA right now, according to analysis of data from the NBA and the Centers for Disease Control.) But NBA players are also outlandishly long—even the "short" ones. At 6'2¾", Wizards guard John Wall might not be able to see the very top shelf at the grocery store, but with 6'9¼" worth of arms, no doubt he can reach it.
The same goes for guys who are labeled undersized but who bring more than just a tough mentality to their ability to "play big." Elton Brand, at 6' 8¼", is diminutive for a power forward, until one considers his condorlike 7' 5½" reach. (A classical Vitruvian Man, then, could have Yao Ming's height and Elton Brand's arms.) Newly minted Lakers center Dwight Howard has a similar build, standing 6' 9" with a wingspan of 7'4½". And the Heat's big three? A total of 19'9¼" tall and 21'2½" long. The only active player included in the SI analysis, which went back to the early 1990s, with an arm length shorter than his height is Magic guard J.J. Redick, who stands 6'4" and has a reach of 6'3¼"—not terribly unusual for a human being but downright Tyrannosaurus rex--ian in the NBA.
And wingspan is more than just a side note to the parade of unusual bodies that is professional basketball. While wingspan—when height is controlled for—is not predictive of scoring, it is predictive of several important statistics. A general manager who wants to add blocked shots would be better off signing a free agent with an extra inch of arm span than an extra inch of height. Anthony Davis, who was taken first overall by the Hornets in the 2012 draft, is 6'9¼" with a 7'5½" wingspan. A player with such a build will get at least 10 more blocks per season than a giant who is 7'1" but who, like most of humanity, has arms that only match his height. "He knows he can block shots while backing up because he can come over the top with those long arms," says Rockets rookie Terrence Jones, who played with Davis at Kentucky and had a jumper swatted by him less than 30 seconds into their first NBA matchup, on Oct. 24. "In practice we always knew we had to do something extra to get a shot over him."
And arm length is equally as important as height when it comes to predicting offensive rebounds. Arm span and height together account for half of the variation among players in defensive boards, without even taking into account factors like playing time, weight and vertical leaping ability. (Strangely in boxing—the sport one might assume favors those with long reach more than any other—arm-to-height ratios aren't nearly as large as in the NBA. But some notable fighters have had gargantuan reaches. Sonny Liston stood 6'½" with a reach of 7 feet. Meanwhile, Rocky Marciano was the Redick of the ring, standing 5' 11" with a reach of just 5' 7", the shortest of any heavyweight champ in history.)
Savvy NBA personnel gurus surely have known this for some time. It's probably no accident that Daryl Morey, the Northwestern- and MIT-educated general manager of the Rockets, who is renowned for his Moneyball approach to hoops, has drafted several of the most superficially undersized players in the NBA. (Among them is Jones, who is 6'8¼" tall with a 7'2¼" wingspan.) Three seasons ago the Rockets made 6'5½" Chuck Hayes the shortest starting center in NBA history. Fortunately his arms are 6'10". The value of such a reach is easy to grasp.