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In the final moments of a tennis tournament, victory might hang on a single sloppy groundstroke or overzealous approach shot. But, if there’s any mistake guaranteed to make tennis players and fans wince in unison, it’s the dreaded double fault. As Deadspin put it last year, a match-squandering faulty serve is “tennis’s most humiliating finish."

Tennis is a sport of strength and speed, but perhaps, more than anything, it's a sport of placement. In addition to practice (and of course talent), a new study, published in the journal Physiology & Behavior, points to something else players can do to get their balls in the right box: sleep more. When college tennis players logged two extra hours of shut-eye each night, public health researchers from Yale and the University of Washington found, they served with more accuracy.

When Roger Federer serves, he tosses and smashes the ball in one fluid motion. But the ease with which he delivers an ace belies the cognitive and physical challenges inherent in serving. To execute a serve successfully, a number of sensory and motor processes have to work in tandem. And they happen to be the same processes that become harder during sleep deprivation, including concentration, balance and alertness.

So, researchers predicted that more sleep would correspond to better serving. To test the sleep-serve connection, they recruited 12 members of the men’s and women’s tennis teams (six from each) at Whitman College in Walla Walla, Washington to participate in a two-week study. 

During the first week, participants slept as they normally would, recording information about nighttime sleep, naps and caffeine consumption in sleep diaries. They also filled out sleepiness assessment questionnaires. On average, they got about seven hours of sleep a night. Though seven hours may not sound paltry, authors pointed out that a solid night’s rest for teenagers means nine hours of dozing. 

At the end of the week, participants showed off their court skills. After a five-minute warmup, they served 25 balls to each side of the court (50 all together). Researchers told them to use their second serves and aim for a target placed in the far corner of the service box. 

The second week of the study mirrored the first in every way except one: Participants slept two more hours each night. And that was a big factor in accuracy: With the sleep bump, results showed, participants hit the serving targets more frequently. Nine of the 12 participants saw accuracy rates improve, most in the 20 percent range. 

Study author Jennifer Schwartz, herself a former college tennis player, told Van Winkle's via email that she didn't think the acuracy gap would have been as significant had the players slept more during the first week, and throughout their tennis careers in general.

If any powerhouse at the U.S. Open is struggling on the accuracy front, perhaps they should skip the Melon Deuce and head to bed. For players slightly more novice than your average Grand Slam competitor, Schwartz pointed out that sleep also facilitates learning and refining one's serve. Brain structures activated during athletic training, she explained, "must be reactivated in order for these motor memories to be consolidated, and the reactivation of these brain structures is most apparent during REM sleep." 

A #hardnine (hours) may keep serves inside the line.