The overtraining warning signs endurance athletes love to ignore

A few winters back, my resting heart rate crept up about eight beats and stayed there for two weeks. I blamed the coffee. Then I blamed the watch strap, and after that a firmware update, which in fairness has been guilty before. At no point in those two weeks did I consider the possibility that the guy doing eleven training hours a week on six hours of sleep might simply be cooked.

I was cooked. It took a head cold, a hamstring that wouldn’t loosen, and the slowest tempo run of my year, all in the same ten days, before I admitted it.

What bothers me in hindsight is that I saw every sign and constructed an alternative explanation for each one. Endurance athletes are world-class at this particular skill, so I want to walk through the warning signs the way they actually show up, with the excuse you’ll be tempted to use attached to each one.

The signals, in the order I usually ignore them

The first one is resting heart rate. If your morning resting heart rate is 5-10 beats above your normal baseline for more than two or three days, something is up. One high reading means nothing. A high reading after a late night or a couple of beers means nothing. A sustained shift in the trend line means your nervous system is dealing with more stress than it can clear overnight. The excuse: “the watch is being weird.” The watch is occasionally weird for a day. It is not weird for ten consecutive days in the same direction. If you don’t already track this, it’s one of the better arguments for understanding your own numbers, which I covered in what heart rate zones mean for endurance training.

The second is sleep falling apart, and this one is cruel because it’s backwards from what you’d expect. You’d think being exhausted would make you sleep like a stone. Instead you get “tired but wired”: you drag yourself through the day, fall asleep fine, then snap awake at 3am with your heart thumping like you’ve had a double espresso. Overstressed athletes run high cortisol and sympathetic nervous system activity at exactly the time it should be quieting down. The excuse: stress at work, or the neighbor’s dog. Maybe. But when bad sleep shows up alongside any other item on this list, the dog is innocent.

Third, you’re getting slower while trying harder. This is the one that should be undeniable, and somehow never is. Paces that were comfortable a month ago now sit a zone higher. Or the inverse happens and your heart rate won’t come up at all: you hit a hard interval and your legs produce nothing while your heart rate sits suspiciously low, like the engine is idling no matter how hard you press. Both patterns mean the same thing. The excuse here is the worst one in all of endurance sport: “I’m just not working hard enough.” So you add volume, which is roughly the logic of digging faster to get out of a hole.

Fourth, irritability. Your partner notices this one before you do. Small things become infuriating. The workout you usually look forward to fills you with dread the night before. Training stress and life stress get processed by the same body, and mood is one of the earliest and most reliable markers researchers have found for athletes tipping into overtraining, more sensitive than most of the blood markers anyone has tried. The excuse: “everyone’s annoying lately.” Sure. Or you are.

And fifth, the big one: dead legs that last for two weeks. Not the heavy legs of a normal hard block, which lift after a rest day or two. This is the version where every flight of stairs feels like an insult, where the first twenty minutes of every run feel like the last twenty of a long one, and where an easy spin doesn’t freshen you up the way it always has. When the usual recovery levers stop working, you’re past the point where one good night of sleep fixes anything.

You don’t need all five. Two of them at once, for more than a week, is enough to act on.

One more thing belongs in this section even though it isn’t a training signal at all: the rest of your life. Your body runs one stress budget, not separate accounts for training and everything else. A brutal month at work, a sick kid, a move, bad sleep from any source, all of it draws down the same reserves your intervals do. The week that breaks you is rarely your biggest training week. It’s a medium training week that landed on top of a hard life week, and your plan had no way of knowing. This is most of why building training around a job is a different problem than following a generic plan, and why the same schedule that felt fine in March can bury you in May.

Why we treat fatigue as a trophy

None of this would be a problem if endurance culture didn’t actively celebrate the disease.

Think about how we talk to each other. Nobody posts their rest day. The training log screenshots that get shared are the monster weeks. “I’m wrecked” is said with a grin. Somewhere along the way, fatigue stopped being information and became proof of commitment, and admitting you need rest started to feel like admitting you’re soft.

There’s also a category error hiding in the word “consistency.” Consistency means showing up week after week for years. It does not mean never missing a session this month. The athlete who trains moderately for forty-eight weeks a year buries the one who trains heroically for ten and then disappears with a stress injury, but only one of those two looks impressive on social media in February.

And the pros make it worse, through no fault of their own. You watch professionals handle twenty-five hour weeks and conclude the human body can take it. It can, if the rest of your life is naps and massage. Yours is a commute and kids who wake up at night. Their training week and your training week are not the same sport.

Overreaching is fine. Overtraining is not.

Some sharpening of terms, because the line between productive and destructive fatigue is real and worth knowing.

Functional overreaching is deliberate. You pile on load for a week or three, dig a controlled hole, then back off and let your body rebound to a higher level. Every decent training plan does this, and the defining feature is that performance comes back within days to a couple of weeks of easing up. The whole logic of a taper rests on this rebound effect.

Non-functional overreaching is the same hole without the climbing out. You backed off and you’re still flat three or four weeks later. No fitness gained, a month lost.

Full overtraining syndrome is the rare, genuinely scary version: months of suppressed performance, hormonal disruption, sometimes a year before things normalize. Most age-groupers never get there, partly because life forces rest on us whether we plan it or not.

The trap is that all three feel identical from the inside on any given Tuesday. You cannot tell which hole you’re in while you’re in it. You can only tell by how fast you climb out, which means the response to warning signs has to be the same regardless: back off early, when it’s cheap.

The fix is rest, and you already know you won’t take it

The entire treatment protocol: three to five days of complete rest or genuinely easy movement, sleep as much as your life allows, eat properly, then re-test with something short and familiar. If you bounce back, it was overreaching. Carry on, a little humbler. If you’re still flat, take another easy week. That’s it. No supplement, no device.

It costs nothing and almost nobody does it.

The resistance is always the same fear: losing fitness. So let me put numbers on it. Meaningful detraining takes around ten days to two weeks of doing nothing to even begin, and a few easy days will cost you literally nothing measurable. Meanwhile the downside of ignoring the signals is the month-long flat spell, or the injury that takes you out properly. The actual choice is three days now, on your terms, or three weeks later, on your body’s.

I know how the three-days option feels. It feels like an emergency. Day two of voluntary rest is genuinely harder for me than any interval session, and I’ve come to treat that itchy, irrational urgency as its own warning sign. Healthy, well-recovered athletes can take a day off without negotiating with themselves about it.

What finally worked for me was making the decision ahead of time, the way you’d set rules for any behavior you don’t trust yourself with in the moment. I wrote down my own triggers: morning heart rate up more than five beats for three straight days, or two 3am wake-ups in a week during a hard block, or an easy run that drifts a full zone high. Any two of those and the next three days go easy, no debate, no checking how I feel about it. Taking the judgment call away from the version of me who is tired, stubborn, and certain he’s fine has saved at least two of my recent seasons from the slow-motion version of that winter I started with.

The other thing I’d say in favor of resting early: it’s diagnostic. Three easy days that fix everything tell you it was ordinary fatigue, and you’ve lost nothing. Three easy days that fix nothing tell you something bigger is going on, weeks earlier than you’d otherwise have admitted it, while the hole is still shallow enough to step out of.

So, the short version. Watch the trend on your morning heart rate. Believe your sleep. When easy pace stops being easy for more than a week, stop calling it a fluke. And when two signals line up, take the rest while it still only costs you three days.

Your fitness is not that fragile. Your season is.