Science sometimes seems so simple. Take rest for instance. With all the experts touting the benefits of recovery, the answer seems straightforward enough, protect players by resting them now or deal with the consequences later. After all, fortunes, literally, can change with a roll of an ankle or twist of a knee.

With the host of factors that affect fatigue and stress, particularly a schedule that asks teams to fly across the country to play games in different time zones, playing time is one of the few factors that coaches can control.

But here’s the problem. Fans come to see the stars, not the understudies. Leagues want their best players on the court, not resting on the bench in Armani and Christian Louboutin.

In fact, rest has become so much of a hot-button issue for the NBA that, prior to the 2017-18 season, the league established rules restricting rest. With fines of at least $100,000, teams are prohibited from sitting healthy players for high-profile nationally televised games, resting multiple players in the same game, or resting players on the road. As a defense, in case they want to sit marquee players, teams like the Warriors have started listing every scratch, contusion and mild injury.

With research touting the benefits of sleep and recovery, teams are now paying more attention to recuperation, trading in old school practices for a more scientific approach. But while teams are wise to pay attention to the stresses of a season, is there such a thing as too much rest?

Recent research suggests that more rest doesn’t guarantee a player or team anything. The article, concentrating on players that missed regular season games because of rest—the so-called “healthy scratch” – presented data on minutes played from 10 seasons of the NBA (2005 through 2015). Using pairs at each position (point guard, shooting guard, forward/center) the study used points per game, assists per game, PER, true shooting percentage, blocks, steals, and number of playoff games as markers of playoff performance.

The study found that players that rested more frequently during the regular season did not perform any better or miss fewer games due to injury than matched players that had rested less. This held true for every position and statistical category studied.

Now, of course this doesn’t indicate that players should be grinding out 40 minutes a night through the 82-game NBA season. The test of a good coaching and sports medicine staff is to find the balance between getting players conditioned for the season and allowing enough recovery.

Teams that run players too hard can be expected to feel the consequences, an example provided by the 4th quarter defensive effectiveness of the Minnesota Timberwolves, currently ranked 29th in the league at 27.5 points per fourth quarter. The Wolves rotation has four players averaging 33 minutes or more per game, more than any other team in the NBA, quite possibly a substitution strategy that leaves players running on fumes by the end of the game.

Another study undermines the belief that rest, and less fatigue, is the key to injury prevention. The article found that the majority of NBA players that tore an ACL did so before reaching their respective average minutes played, presumably before they were fatigued. “Our findings are interesting because the common thinking is that as these players get more tired at the end of the games they are more likely to be injured,” says Kelechi Okoroha, the lead researcher of the study, “However our study disproves that idea as ACL injuries are often due to a multitude of factors.”

In a similar fashion, the majority of players were injured at the beginning of the season, when legs are less taxed by the heavy workloads. Okoroha reasons that, rather than fatigue, the injuries might be more attributed to a lack of conditioning.

Of course it may also be that other types of fatigue play a more prominent role in injury, mental fatigue for instance. Mentally demanding tasks – like the concentration required to compete in professional sports – can diminish performance and raise injury risk. So instead of solely physical rest, perhaps players need some mental rest from the slog of a professional season.

In the NFL, the reasons behind the high rate of injury have been studied, publicized and, frequently, criticized. But one of those reasons, a player’s workload, might be less linked to injury than previously thought. Research performed at the University of Colorado Sports Medicine and Performance Center found that running backs in the NFL, the most injured position in the sport, with a high number of carries were not at increased risk of injury or diminished performance during the following season.

The authors hypothesize that the finding may simply be explained by the fact that running backs with a high number of carries are not only talented athletes, but also perhaps possess an innate ability to avoid injury, making them more durable and less injury prone. But the hardiness of the high-carry running backs wasn’t related to size or weight, as body dimensions did not predict the risk of injury.

On the surface, resting players, in efforts to limit exposure to injury or promote recovery, isn’t as clear-cut a decision as fans might think. Teams get better, and stay hot, by playing games. In fact in baseball, rest might not offer much advantage at all, as since 2006, the team that won its league championship series first has lost 10 of 11 World Series.

“There’s a balance between rest and performance,” says Brandon McDaniel, major league strength coach for the Los Angeles Dodgers, “Baseball is a highly skilled sport that doesn’t rely on raw athletic abilities like running and jumping.” According to McDaniel too much rest can take a player out of rhythm and increase the risk of injury because the body hasn’t developed the tolerance needed to handle 9 innings.

“The most important thing to do (to avoid injury and maintain performance) is to maintain the rhythm,” says Fergus Connolly, director of performance and football operations for the University of Michigan football, “Change is the critical factor, not the absolute amount of rest.” Connolly believes that many injuries – the high number of preseason football and basketball injuries for instance – are caused by the quick increases in intensity that follow a long offseason.

Truth is, figuring out how much rest a player needs isn’t so easy. For coaches, solving that puzzle might be the difference between winning and losing.