Without any notice, either to reporters or the player himself, the Eagles held DeMarco Murray out of team drills on Sunday, the first day of training camp. (He did run position drills, though.)

This naturally raised a lot of speculation about his health, after endless discussion about the insane workload that Dallas subjected him to last year (392 carries plus 64 receiving targets in the regular season, and another 44 and 6 respectively in the playoffs). Many running backs have struggled after a year with a heavy workload in the high 300s.

So it wouldn't really surprise anyone if the Eagles wanted to keep Murray's load on the light side during training camp this year. But it was a big surprise to rest him on the very first day back from a six-week vacation. This led to lots of worry and wondering. Is Murray already injured, or completely worn out from last year before this one even begins?

We don't really know. But it's probably not a serious problem like that. There is no indication that Murray is injured, and he worked out rigorously Monday with no sign of holding back. He told reporters after practice that he was fine and had no idea why he was held out on day 1.

The most likely explanation is that the Eagles sports science monitoring, which I discuss at length in my new book "Controlled Chaos," told the team that it was time to rest Murray. Not that he's injured or irreparably damaged, just that he needs to chill today. This monitoring is not a long term warning -- it's a very short term indicator, like the engine heat dial on your dashboard.

Contrary to what a lot of people think, the focus of that monitoring is not to test a player's strength or potential, or whether they've been getting high or eating junk food. Monitoring is designed to test how much of a player's potential he is using. The team doesn't want players to leave too much of their strength untapped, but mostly they want to avoid players hurting themselves by pushing too hard.

Elite athletes are usually great at pushing themselves hard. That's how they became elite. But it's always been hard to figure out how close they are to the cliff. Part of the drama of high-performance athletics is that players can discover reserves they didn't know they had, usually in epic clutch moments (such as playoff games).

But they can also push themselves too hard to the point where injury is more likely, and their recovery back to full potential will take an unsustainable amount of time. Unless you're in the middle of the Super Bowl, needing a week to recovery from your intense effort is disastrous during the season.

At the same time, these monitors -- at least in theory -- can also tell you if a player is not pushing themselves to somewhere at least near their limit. Chip has exhibited scorn toward some players who where slow to come back from injuries, such as Mychal Kendricks and Earl Wolff. My suspicion is that the monitors said they were ready to go, and the players themselves disagreed. Chip's obvious frustration makes more sense if he had scientific data contradicting the player's reluctance. Otherwise, how could you know?

To get a sense of what this monitoring works, I recommend an article by a runner who tested the Omegawave machine, which the Eagles also use. This is very fine-grained data about what to do on a day-to-day basis. The machine gives you scores in five categories, Cardiac Readiness, Resting Heart Rate, Stress, Recovery Pattern, and Adaptation Reserves. These help you determine individually how hard you can work that day.

Every morning before a practice, the Eagles monitor players, collect their sleep data and test their hydration, and give them a questionnaire to fill out about about how they feel, any aches and pains, etc. In "Controlled Chaos," I quote Chip telling Ross Tucker (on a little-noticed podcast) that

"On an individualized basis we may back off. We may take [TE] Brent Celek out of a team period on a Tuesday afternoon and just say, 'because of the scientific data we have on him, we may need to give Brent a little bit of a rest.' We monitor them very closely."

That sounds a lot like what went down on Sunday. But how could this happen on the first day of training camp after a month and a half vacation? Because, as DeMarco told reporters, he worked out a lot during his "vacation." (He's also a newlywed; make of that what you will.) The Eagles are collecting players who work out eagerly on their own, and this monitoring is about making sure they don't overdo it.

The good news -- assuming I'm right about all of this -- is that it means there is no long term concern here. This is a short term, moment to moment adjustment. The Buffalo Bills use similar sports science monitoring, and told Kiko Alonso to dial it back one month into his rookie year workouts. Alonso went on to a great season, with 159 tackles (3rd in the NFL) and 4 interceptions.

We'll see if we can get Chip Kelly to discuss Murray's day of rest on Sunday at the press conference today. But all indications are that this is not anything serious to worry about.

UPDATE: At his press conference today, Chip Kelly confirmed that DeMarco Murray was held back on Sunday because of the result on his hydration test, which is a day to day thing. Chip literally said that Murray "was a little high" on the test, but his response to a followup question made it clear that he meant that Murray was a little dehydrated.