Usually, when the San Francisco 49ers and the Los Angeles Rams play, it’s a relatively short commute. But this evening, the teams will kick off the NFL’s first-ever regular-season game in Australia.

The two teams have taken diametrically opposite approaches to preventing the 8,000-mile journey from disorienting their stars. The 49ers boarded their 16-hour flight to Melbourne nine days ago and have spent the intervening time training, watching Aussie rules football, and winning the majority of local support. The Rams landed yesterday, just 24 hours before the game. They’re betting on being in Australia so briefly that players’ brains and bodies won’t notice the difference. That makes the game the most high-profile test of jet-lag-evasion techniques in American sports history.

Anyone who has hurled across several time zones in one go knows how wide-awake and helplessly sleepy you can feel at inappropriate hours upon landing—a major inconvenience for professional football players, whose career depends on how they perform during one very specific period. Circadian rhythms can also affect performance in less obvious ways. Compounds that encourage inflammation, for instance, spike at night, when the body is doing less and can direct more energy toward fighting infection. A new time zone throws that optimal function off tilt and can cause stomach issues, cognitive impairment, headaches, and mood changes.

Teams at a circadian disadvantage tend to play worse. One study that analyzed every NFL game from 1970 to 2011 with a kickoff after 8 p.m. ET found that West Coast teams did better than oddsmakers expected in two out of every three games, regardless of whether they were home or away. Head coaches are also more likely to make the risky call to attempt an offensive play on a fourth down during evening games when they travel west compared with any other direction.

Because the consequences of jet lag are well established, the real question is how to avoid them. In 2021, 26 sleep researchers and clinicians articulated their best answer in the journal Sports Medicine. Among other recommendations, they noted that fully recovering from jet lag takes one day for each time zone crossed. The 49ers seem to have followed that model by leaving more than a week ahead of the game. (Melbourne is 17 hours ahead of California, but for body-clock purposes, that’s the same as being seven hours behind.) Kyle Shanahan, the 49ers’ head coach, told reporters last month that he would have loved to have just shown up in Australia the day before but that the experts he’d spoken with had all recommended arriving earlier. “I was a little bit on the fence,” he said. “Science wasn’t.”

The Rams, by contrast, are attempting to not switch their body clock at all. They have spent the past few weeks practicing in the late afternoon, which aligns with Friday’s mid-morning kickoff in Melbourne. Their head coach, Sean McVay, said at a Sunday press conference that the team will “have kind of a rhythm” when they land. “We’ve tested it out with some guys, and we feel like it’s been positive,” he added. The strategy is not without precedent: In 1994, Allen Johnson, an American hurdler, decided to live as if he were on East Coast time when competing in European tournaments. His coaching team strongly disagreed, but he won four world championships and Olympic gold. Last year, the Rams arrived in London the day before a game against a strong Jacksonville Jaguars team and won.

Jamie Zeitzer, a circadian physiologist and a co-director of Stanford’s Center for Sleep and Circadian Sciences, described the Rams’ strategy to me as “high risk, high reward.” If the Rams really feel as though they’re playing in the afternoon, they might have a slight advantage over opponents who feel as though they’re playing in the morning. During the late afternoon, circadian rhythms prompt optimal muscle strength and coordination, and core body temperature peaks, increasing alertness with it. Plus, a week might not be long enough for the 49ers to stop suffering the effects of their travel. Some people just take longer to recover, and a long-haul flight, jet lag, hotel life, and unfamiliar foods can lead to days of poor sleep, Zeitzer said. The 49ers have spent their September experiencing time as a pliable, erratic force. Shanahan told reporters that he was “a little confused” in a recent press conference, during which he also struggled to identify the day of the week. (It was Monday.)

Still, Zeitzer thinks the Rams have chosen the worse jet-lag strategy. If the players are to get any rest at all, their 24-hour stretch in Melbourne before game time needs to be carefully managed. From his experience consulting with professional teams, adults are hard to control. Meeta Singh, a doctor who has served as a sleep consultant for multiple NFL teams, thinks that players simply won’t be able to sleep. Singh is one of the co-authors of the Sports Medicine recommendations, which suggest that athletes maintain a “reduced exercise schedule” and do hand-eye-coordination drills in the 72 hours after a long-haul flight. The Rams won’t even be in Australia for 72 hours.

Sleep became a major metric for all sorts of professional sports teams after the NBA distributed more than 2,000 Oura rings to its players during the depths of the coronavirus pandemic. “Once you can show a coach numbers, sleep stops being a soft topic and becomes something they can manage, like training load or nutrition,” Singh told me. Many NFL teams now have a sleep specialist and a performance-science team working on circumventing jet lag. To prep players for time shifts before they depart, 14 NFL teams, including the 49ers, have installed in their training facilities lighting systems designed to mold circadian rhythms. The system, called BrainLit, mimics daylight according to a “recipe” that each team specifies, Kyle Harris, the CEO of the company, told me. On the 49ers’ flight to Melbourne—on the world’s largest and most expensive passenger airliner, with lie-flat seats that extend to seven feet—each player received his own sleep guidelines. Tom Clark, a sports scientist who advises NFL teams with international games, told me that many teams establish each player’s chronotype, or natural preference to sleep and wake at certain hours, and use that information to prescribe optimal sleep habits.

Roger Goodell, the commissioner of the NFL, eventually wants 16 international games to take place each season. By the time Super Bowl LXI rolls around this February, teams will have played in Rio de Janeiro, London, Paris, Madrid, Munich, and Mexico City. For future seasons, the league is considering adding games in the United Arab Emirates and Japan; Goodell insists that an NFL team will be based outside the U.S. in his lifetime.

Perhaps such a punishing schedule will settle debates once and for all about how to handle jet lag. Whatever the marginal impact of sleep strategy, though (and some games are decided on the margins), usually “the better team will win even if they’re playing on the moon,” Clark said. And the Rams are this year’s Super Bowl favorites.