Baylor’s Brittney Griner became the second women ever to dunk a basketball in an NCAA tournament game Tuesday in a win over Florida. There are multiple dunks in every men’s game. Why are there so few jams in women's basketball?
Leaping ability. The average WNBA player, at just under 6 feet, is about 7 inches shorter than her male counterpart. (Average data for all collegiate female players isn’t available.) Height is only part of the problem, though—plenty of 6-foot male players can dunk. The gender gap in vertical leaping ability is also substantial. The average female college basketball player has a vertical leap of approximately 19 inches, compared with more than 28 inches for the average male player. Since you have to get your fingers about 6 inches above the rim to have a chance at dunking, a female player of average leaping ability would have to be around 6-foot-6 with a standing reach of 8-foot-11”—the approximate measurements for Michael Jordan. (His Airness reportedly had a 48-inch vertical leap.) Few female players are that tall, and none of those giants is an exceptional leaper.
Still, the paucity of dunks during women’s games gives a slightly false impression of female dunking ability. Dunking in practice is somewhat more common, but many coaches advise against attempting a rim-rattler when it counts because of the risk of injury or throwing away an easy deuce. The late Oklahoma State coach Kurt Budke, for example, forbade forward Toni Young from dunking after she broke her arm in three places while completing one during practice in 2011.
The gender gap in leaping ability is wide at every level of competition. According to a 2004 study of medical students and their spouses, the average male in his 20s can out-jump 95 percent of females in the same age group. And men seem to have a peculiar advantage in jumping compared with other athletic pursuits. According to a study of world records for track and field events as of 2004, men had a 15 to 16 percent advantage (PDF) in high jump, long jump, and triple jump. The gender gap in running events was only 10 to 13 percent. (Pole vault featured the biggest difference at 23 percent, but that’s likely because women have participated in that sport at the Olympic level only since 2000.) The difference between men and women has been relatively stable since 1983.
Researchers are still working out why men can jump so much higher than women, on average, but it clearly starts in puberty. Boys experience a spurt of muscle growth during the hormone surge, and their vertical leaping ability increases accordingly. Girls, in contrast, actually lose takeoff force during puberty. In addition, some studies have suggested that men have a higher ratio of fast-twitch to slow-twitch muscle fiber, which provides a substantial leaping advantage, although these results are controversial. The male physiology also seems to be more efficient at recruiting all the necessary muscles to work together to accomplish a task. That means a man could typically out-jump a woman who had the same muscle structure.
There’s hope for young girls who dream of playing above the rim. Historically, pediatricians and trainers have cautioned against serious athletic training in young children. They feared that weight lifting would close growth plates or cause muscle tears. But researchers increasingly believe those concerns are overstated and that women can significantly narrow the gap in leaping ability that opens up during puberty through moderate resistance training before and during the period of hormonal changes.
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Explainer thanks David Patterson of ATSU-Kirksville College of Osteopathic Medicine and Carmen Quatman of Ohio State University. Thanks also to reader Josh Hummert for asking the question.
Correction, March 27, 2012: This article originally misidentified the Kirksville College of Osteopathic Medicine as the Kirkman College of Osteopathic Medicine.