FOR DECADES, the story of a major league game has been told by the familiar numbers in a box score: runs, hits, errors, home runs, strikeouts.

But now, there is another chart your favorite team looks at after games, one that few outside the sport's inner circle have seen, consisting of color-coded gridlike documents that measure the workload of every player who took the field that day.

Baseball might not be the first sport that comes to mind when you hear the term "load management," but MLB teams are becoming obsessed with it. In baseball, the discussion is about keeping position players on the field and performing their best.

Teams monitor everything players do, starting with the obvious -- how much distance has he covered on a given night, both on the basepaths and defensively in the field. Tracking also takes into account the small details that go into the equation -- how many times did a player take off from first base on a full count? How frequently did he dive for a ball in the infield? Each bit of information helps teams get ahead of potential health problems or dips in production.

"I've taken a lot of interest in it in my second career as a manager," Cincinnati Reds skipper David Bell said. "As a player, you think you're invincible and can play every day. But the grind of the season in baseball is an extreme challenge. Over time, it's compounded.

"The grind is harder. The game is more difficult."

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At a time when analytics have become a standard element of almost every front office decision, optimizing player workload is seen as one of the few remaining areas teams can gain an edge. Now that technology has emerged to allow clubs to measure movement like never before, the race to find the best information -- and how to communicate it to players -- is on.

"There are other sports that are way ahead of us," Milwaukee Brewers general manager Matt Arnold said. "Soccer and NBA teams have been tracking this kind of stuff for years. We have room to grow in our industry."

With clubs learning every day, ESPN asked MLB executives, managers and players what the increasing interest in load management means to their sport -- and how their teams are using the data.

In a sport where just about everything is tracked, front offices are working with players to create rest plans by monitoring their on-field movements. Troy Taormina-USA TODAY Sports

THERE IS NO other sport that demands its athletes take the field as often as professional baseball does. Sure, MLB players aren't tasked with constant running, but every movement adds up and leads to a cumulative fatigue over the length of the season.

"You might go 10 games without ever accelerating, but you might throw a bunch from the outfield," Chicago Cubs general manager Carter Hawkins said.

Enter the grids, which track each of those movements cumulatively. The San Diego Padres, for example, track workloads for their players in running 30-day increments, using sheets color-coded for high-effort runs, top sprint speed and taxing defensive movements. Some teams believe their information is proprietary, keeping it close to the vest. Everyone has a different slant as to how they track load management.

"We have a report that comes out every morning that includes what's pertinent from the last game," Justin Hollander, Seattle Mariners executive vice president and general manager of baseball operations, said. "Sort of a running total on where guys might be at, based on workload over a longer period of time."

ESPN was granted permission to observe several teams' load management grids, and while the tracking tools look different in every front office, there is a common theme in many of the printouts: The darker the color, the more that player has moved around, often on a gradient of white to dark red.

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As you would expect, baseball's biggest stars often have their names in the darkest hues, as they are in the lineup every day and, with a few exceptions, run the bases more than the average player.

"He lives in the red zone," Houston Astros manager Joe Espada said of two-time All-Star third baseman Alex Bregman.

Once a team has identified a player entering that danger range, the process shifts from spreadsheets to action plans. The challenge in adjusting pregame and postgame work is that fatigue is a moving target. Is the team in a stretch of the schedule without days off? Did it play extra innings recently? And what has the player actually been doing on the field?

"We have a more evidence-based way to measure where you're truly at, fatigue-wise," Hollander said. "I think a lot of teams incorporate that into routines, work you do in pregame, work you do in postgame and, of course, days off."

Each manager faces a different challenge. After his team's deal for Luis Arraez, Padres manager Mike Shildt must rotate a crowded group of infielders between their regular positions and DHing. In the Astros' case, Espada is particularly cognizant of the additional workload over the past few years thanks to the team's postseason success. As one rival executive put it: "The whole team lives in the red zone."

"I take into consideration that our players have played the most games of any team over the last six, seven years," Espada said. "When guys are starting to trend in the red zone, we try to make sure to control the volume of their pregame work or give them a day at DH or a day off. But we try to do that before they get into the red zone."

MLB managers, like San Diego's Mike Shildt, often become the middlemen in communicating the front office's load management findings to the players in the clubhouse. Sean M. Haffey/Getty Images

FRONT OFFICES ALSO face the reality that players don't all love the idea of being told to sit down because a heat map says it might be time. It's been ingrained in many of them to play every day no matter how their bodies feel, and some simply prefer to play through fatigue rather than listen to what tracking technology tells them.

Cubs shortstop Dansby Swanson had that mindset, playing in all but two regular-season games from 2020 to 2022. Now, though, a late-season dip in production at the end of last year and a slow start to this season have him thinking differently.

"I don't like changing what works for me but I've had to this year, in order to be the best player possible," said Swanson, who turned 30 during the offseason. "We all sat down and collaborated on a new [pregame/postgame] plan that would work for me like just two weeks ago.

"It's a different way of putting pennies into the piggy bank."

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Other stars still prefer the heavier workload, fearing that sitting even for a game will hurt their production more than resting would help it.

"I feel like I play better when I'm in the red," Bregman said. "I feel like I show up to the ballpark to play every single day and I want to play 162 plus postseason every year."

This is where front offices and coaching staffs have learned to collaborate with players, finding ways to lighten their load behind the scenes while still allowing them to appear in games. The manager is often the middleman between the medical team, strength coaches and players.

In the Astros' case, Bregman works with Espada to control pregame volume. Padres infielder Xander Bogaerts does the same with Shildt, starting with eliminating batting practice and then, if needed, cutting down on lifting weights.

In his first year as San Diego's manager after spending last year as the team's bench coach, Shildt has learned that telling a player he needs to take a game off isn't the best approach. Instead, he'll suggest a DH day or an altered plan for before and after the game.

"If that collaboration isn't taking place and we don't mesh those things appropriately, you're going to have a much higher risk of injury or poor performance," Shildt said. "From my seat, what's important is the daily schedule. We monitor the efficiency of the pregame work. That's the best word to use, I think. How efficient are we with our work beyond the game?"

As the concept of load management spreads through baseball, the sheets telling the story of a player's status might look a little different in every front office. But the goal for every team is the same: Getting ahead of fatigue so players can perform at their best -- instead of learning too late that they could have used a day off after experiencing an injury or a prolonged slump.

"It's not about trying to limit anybody," Arnold said. "It's about keeping them on the field as much as possible."