We are proud to present the following excerpt from ‘Good to Go: What the Athlete in All of Us Can Learn from the Strange Science of Recovery’ by award-winning journalist Christie Aschwanden, out now in paperback.

Tom Brady’s pajamas arrived on my doorstep in two space-age pouches that looked like they might contain Starfleet uniforms. Unzipping the silver pods, which had the slogan “Rest. Win. Repeat.” debossed on the lids, I found what looked like ordinary sportswear, matching pieces in black synthetic fabric. The shirt, long sleeves with a scoop neckline and five buttons down the front, felt soft and stretchy. The bottoms, with an elastic drawstring waist and elastic cuffs at the ankles, were made of the same thin, pliable material and had a small blue crescent moon printed on the butt.

Retailing at $199.98 for a complete set, TB12 sleepwear isn’t cheap, but these weren’t ordinary pajamas—they were scientifically developed recovery technology, according to Under Armour, its maker, and to New England Patriots quarterback Tom Brady (number 12), its eponymous endorser. The inside of the material was printed with a hexagon pattern containing the bioceramic powder purported to give these jammies their magic. The bioceramic material supposedly absorbs body heat and reemits it as far infrared radiation. “The far infrared, when it’s against your skin, ends up reducing inflammation,” Brady says in a video on the Under Armour website. “Without the sleepwear, I don’t really feel like I would have been able to achieve the things that I have done and hope to continue to do.”

It seemed like a bunch of overwrought marketing, but if these pajamas were really the key to Brady’s athletic longevity and success, I was willing to give them a try. I’m just a few years older than Brady and entering an age in which promises of youth hold a certain allure. I’d just gone for a long, hard cross-country ski and was feeling pretty beat, so I figured it was a good night for the first test.

My initial impression was that they were comfortable, at least for lounging around before bed. The garments were pretty much indistinguishable from any other Under Armour performance clothes. They looked and felt like regular wicking tights and shirts. The light fabric was soft against my skin, and even though the pajamas covered my body from neck to ankle, they didn’t feel constricting or overly warm. I’d suspected that their trick was heat, which usually feels good on sore muscles. Instead, they felt strangely temperature-neutral—not particularly warm or cold. I crawled under the covers and fell asleep as usual. I didn’t notice anything different about my sleep or how I felt the next day upon waking. My run the next day felt as it usually would. I didn’t feel any more or less recovered than usual. I tried them on multiple nights. If the pajamas had enhanced my recovery, the benefit was too minuscule for me to detect.

“Brady claims the FIR from the fabric reduces inflammation, but it’s not clear how that works and there’s scant evidence for this claim.”

“The goal of the sleepwear is to unlock better sleep,” Glen Silbert, who was then Under Armour senior vice president of global product, told me. Silbert didn’t explain what it was that was keeping sleep locked up, and when I asked if the garments worked by reflecting heat, Silbert said no. “It’s not taking heat and returning heat. It’s basically taking heat and returning it in far infrared, which is not heat, it’s an energy.” I was surprised to hear that, because according to the research paper that Under Armour pointed to as proof of the scientific principles behind their far infrared technology, “FIR transfers energy purely in the form of heat which can be perceived by the thermoreceptors in human skin as radiant heat.” In other words, the sleepwear absorbs body heat and reflects it back as, wait for it . . . radiant heat. Just like the infrared sauna that radiates a special heat called “infrared.” To be fair, the pajamas are supposedly emitting the heat at a different, lower-energy wavelength, for whatever that’s worth. (Whether far infrared radiation is heat or not is a matter of semantics, but for all practical purposes the two are synonymous. We can’t see far infrared radiation, we can only sense it as heat.) In the promotional video, Brady claims the FIR from the fabric reduces inflammation, but it’s not clear how that works and there’s scant evidence for this claim. Anyway, decreasing inflammation might actually be a bad thing if you’re hoping for a training response.

Silbert told me that lab tests of the sleepwear had shown that it “helps you go to sleep faster and sleep more restfully—meaning you wake up fewer times in the night and ultimately sleep longer.” I didn’t notice any of these effects in my trials, but Silbert assured me that “there’s real science behind it. Tom Brady was our proof of concept.” The evidence, he said, lies in Brady’s performance. “At 39 years old, you could argue he plays like a 23-year-old. He is the best quarterback in the game, and I don’t think he’s played better than this year,” Silbert said of the 2016–2017 season that ended with Brady’s team winning the Super Bowl.

I could only shake my head. Tom Brady probably is one of the NFL’s best quarterbacks, but he was a successful football player before he signed his name to these pajamas, and to attribute his success to the bioceramic powder in his PJs seems far-fetched. The real trick here isn’t pixie dust, it’s something far more powerful—sleep. Brady is known for hitting the hay early, and his 8:30 p.m. bedtime and good sleep habits are a more likely contributor to his performance and longevity than any special clothing (or the luxury mattresses he also promotes, for that matter). Still, there’s a reason Brady and Under Armour are commodifying sleep—it works. Insofar as there exists any magical secret for recovery, sleep is it.

The benefits of sleep cannot be overstated. It’s hands-down the most powerful recovery tool known to science. Nothing else comes close to sleep’s recovery-enhancing powers. You could add together every other recovery aid ever discovered, and they wouldn’t stack up. Going to sleep is like taking your body to the repair shop. While you doze, your body’s recovery processes ramp up to fix the damage you did during the day and get you ready to perform again.

Throughout the night, we cycle through four stages of sleep. Stage one is when we transition from wake to sleep, is considered the lightest stage of sleep, and usually takes up about 5 percent of our total sleep time. Next comes stage two, where we spend about 50 percent of the night and which is harder to wake from than stage one and may be important for some memory processing. Stage three is the deepest stage, which is also associated with memory processing and is when the body releases substances like testosterone and growth hormones to push tissue repair into high gear. Skimping on sleep can blunt the release of hormones involved in muscle building and rejuvenation. In one small study, healthy young men who slept only five hours per night for a week experienced a 10 to 15 percent dip in their testosterone levels. Stage three is also where factual learning is encoded in the brain and superfluous memories are pruned. The final sleep stage is REM, or rapid eye movement, sleep in which most dreaming happens. Procedural memories seem to get enhanced during REM sleep, so for athletes in a sport that involves motor or cognitive skills, this phase of sleep is especially crucial. REM episodes get progressively longer as the night goes on, so when you skimp on sleep, you’re depriving yourself of REM sleep.

Tom Brady makes the case for sleep in The Tortoise & The Hare & Tom Brady, an illustrated tongue-in-cheek promotional children’s book produced by Under Armour and written by the comedy group Funny or Die. In the story, Mr. Tortoise sends Brady a text message (“tom brady u suck at football”) challenging him to a game. As he prepares for the challenge, Brady shares his tips for good sleep, which read like a page out of an expert’s guide to sleep, with some pitches for his TB12 products thrown in, of course. In one scene, Brady tells a framed photo of Boston, “This recovery sleepwear will help my body recover faster as I sleep.”

“The benefits of sleep cannot be overstated. It’s hands-down the most powerful recovery tool known to science.”

Before snuggling under the covers, Brady turns down his thermostat. “There. 65 degrees Fahrenheit. My ideal temperature for restful sleep,” Brady whispers to his four Big Game victory rings. “The rings winked at him, as they do every night.” Winking aside, Brady’s right about the temperature—65°F is cool but not cold, an ideal temperature for sleeping.

Brady also shuts down his devices 30 minutes before bedtime. With his phone safely tucked in a special box to prevent it from distracting him, Brady dons his spectacles (just for show, of course—his vision is perfect) and settles in with his favorite book. This is totally solid advice. A small study by researchers at Brigham and Women’s Hospital compared the sleep patterns and circadian rhythms of volunteers who read on an electronic device before bed to those of volunteers who read print books instead. It found that those staring at a screen had suppressed melatonin levels, a delayed circadian clock, and reduced alertness the next morning compared to those who’d read print books. Research suggests it’s the blue light emitted by computers, tablets, and phones that disrupts our body clocks, so apps like F.lux, which progressively reduce blue light as the night progresses, can help cut the risk for those who can’t live without pre-bed screen time.

As he’s about to doze off, Brady gets a visit from Mr. Owl, who says, “Tom Brady, don’t forget your ear plugs. A quiet environment is crucial to your good sleep.” More solid advice—in addition to a consistent bedtime and wakeup time, a good sleep environment free of incoming noise, light, and other distractions can help optimize sleep.

While Brady is getting a head start on rest, Mr. Tortoise is down at the bar, slamming back shots of carrot juice. No surprise, Brady wins the game by 200 points, but he’s such a good sport that he shares some TB12 brand electrolytes with Mr. Tortoise and Mr. Hare after the game.

“It’s become common in some circles for people to brag about how little sleep they’re getting, as if sleep deprivation is some sort of status symbol.”

Sleep is when recovery and adaptation happens, and prioritizing it can help athletes flourish. The optimal amount of sleep varies by person. “I tell athletes, if you didn’t set an alarm, how long would you sleep?” says Erik Korem, former director of sport science for the Houston Texans NFL team. “Here’s what I want you to do—go to bed at a normal time in a dark, cold place with no alarm. When you wake up, use that as your starting point.” He tells players, “You’re striving to find the sweet spot. As a general rule, that’s seven to nine hours of sleep per night.” Korem encourages his athletes to pay attention to when they’re sleeping, though it’s up to them to decide whether they want to formally track it. “The biggest thing is just awareness,” he says. Once athletes start paying attention, “They realize, oh yeah, I only got six hours of sleep last night and this is how tired I feel, maybe tonight I’ll go to bed earlier.”

It’s become common in some circles for people to brag about how little sleep they’re getting, as if sleep deprivation is some sort of status symbol. I recently met a renowned neuroscientist who boastfully blamed four hours of sleep for his difficulty carrying on a conversation. (He was so busy with all his startups!) But neglecting his body’s basic needs was really just a sign of self-delusion. Yes, a few lucky “short sleepers” are genetically inclined to thrive on only about four hours of shut-eye per night, but this condition is extremely rare. “Most of the time when someone says they only need five or six hours of sleep, what that means is that their ability to tolerate sleep deprivation is better than most,” says Meeta Singh, a sleep specialist at the Henry Ford sleep laboratory. “They’re actually walking around with sleep debt, and have forgotten what it feels like to be awake and alert.”

Research shows that people who are chronically sleep-deprived lose their normal perception of sleepiness and become poor judges of their neurocognitive performance, says Sigrid Veasey, a physician and sleep researcher at the University of Pennsylvania. When people are limited to five hours of sleep per night for a week, they report feeling very sleepy after the first night, but chronic sleep loss blunts the sleep drive, so after a night or two, the person doesn’t feel as sleepy as they should. “You think you’re functioning okay, but you’re not,” she says. You might be able to do rote memory tasks on five hours of sleep, but anything that requires trouble-shooting or complex thoughts will become increasingly difficult.

“It’s practice, with sleep, that makes perfect.”

Skimping on sleep is like showing up to the game drunk. “If you only get six hours of sleep, you double or triple your normal reaction times,” Singh says. She points to a study in which researchers subjected volunteers to either doses of alcohol or sleep deprivation and then gave them a battery of tests on attention, reaction time, and sleepiness. The results showed that people who’d only spent six hours in bed were as impaired as those who’d consumed two to three beers, while four hours of rest was equivalent to about five or six beers. Staying up all night was like throwing back ten to eleven beers and then trying to function normally.

If you’re forced to pick between some extra shut-eye or an extra workout, it’s wiser to pick the sleep, Singh says. Sacrificing an hour of sleep to make a morning workout is totally self-defeating.

Without proper sleep, the body becomes fragile. Studies at the Henry Ford Sleep Lab have shown that skimping on slumber makes people more sensitive to pain, and a study of high school athletes found that sleeping fewer than eight hours increased the risk of injury. Sleep deprivation can also suppress the immune system and make you more susceptible to viruses. In one study, researchers measured the sleep patterns of 164 people over the course of a week, and then brought them into the lab where they were quarantined and given nasal drops containing a cold virus. The people who’d slept an average of six or fewer hours per night during the previous week were far more likely to develop a cold than those who’d slept seven or more hours. Forty-five percent of the people who’d slept five or fewer hours got sick, while less than twenty percent of the volunteers who’d averaged seven or more hours of sleep came down with a cold.

Whole books have been written about how much practice athletes need to succeed at the highest levels, but if it’s not paired with sufficient sleep, even 10 million hours of practice won’t help. Sleep reinforces motor skills learning, and sleep in the initial 24 hours after training seems especially crucial—a finding that led researchers Matthew P. Walker and Robert Stickgold to propose that “It’s practice, with sleep, that makes perfect.” After an afternoon working on your tennis serve, golf swing, or swim stroke, you need a full night’s rest to make the lessons stick.

Sleep is the number one thing that athletes can do to bounce back from their training. It’s like the cake of recovery. Everything else is just icing.