Exercise progress is a delicate balancing act. Space your workouts too far apart and you’ll fall short of your full potential. But skip out on recovery days or push yourself too hard and you risk stalling out or burning up muscle as fuel.

For the most serious athletes, the biological phenomenon is often referred to as overtraining or overtraining syndrome. But for most weekend warriors, the risk falls under the slightly different category of overreaching.

It might sound like a nitpicky naming convention, but which one you’re suffering from—overreaching or overtraining—makes a big difference.

“Rarely anyone other than high-level of Olympic athletes get to the point of actual overtraining syndrome,“ says Minnesota-based exercise physiologist Mike T. Nelson, Ph.D., C.S.C.S. “It takes months or years to recover from, and the athlete might never be able to compete again.”

Overtraining syndrome, in other words, is a serious problem. It involves a barrage of symptoms such as decreased motor coordination, force production, and glycolytic capacity, alongside the possibility of recurring infections, sleep disturbances, and depression.

Overreaching, however, is common among hardcore recreational athletes and health nuts. You may at times be guilty of it yourself—and that's not necessarily bad. While overreaching can be a step on the path toward overtraining, it can also help you hit your fitness goals—but only if managed properly. Short-term periods of overreaching, if followed up by proper recovery or a de-load week, can result in significant strength and power benefits, according to findings published in the Journal of Strength and Conditioning Research. This is referred to as “functional” overreaching.

The most common example of functional overreaching is the pre-marathon taper: By running too hard and too far for a couple of weeks, and then cutting back big time during the week before the race, the runner’s race-day performance gets an even bigger boost. In more extreme cases of overtraining, taking a full two weeks off of all training may be required to get performances back on track, Nelson says.

The key to overtraining strategically is knowing when to pull back, says Gavin McHale, a Winnipeg-based kinesiologist and certified exercise physiologist. If mismanaged, functional overreaching can quickly turn into non-functional overreaching, which can sideline performances for weeks or even months, he says. That's long enough to throw off your gym gains and seriously screw up your summer racing plans. Symptoms of non-functional overreaching include altered heart rates, wonky hormone levels, poor moods, and, of course, decreased exercise performance.

Avoiding that can be tricky, and it involves a high degree of self-awareness. “Preventing non-functional overtraining is really more than an art than a science at this point,” Nelson says. “It’s about listening to your body and responding in a way that moves your progress in the right direction.”

That might mean getting extra sleep, cutting out processed foods, quelling work stress, or, if all else fails, dialing back your workouts. As far as your body is concerned, stress is stress—whether it’s due to late nights, heavy deadlifts, or one too many late nights spent in the company of cheeseburgers and beer. You have to manage all of it.

To help you avoid sidelining yourself, we asked Nelson and McHale to talk us through the signs of overreaching. These aren’t necessarily dangerous, but you should still pay attention. To keep you fitness on track, it’s important to act fast to the symptoms below.

1. You’re Experiencing Sluggish Exercise Performance

Sure, we all have “off” days, but if for a week or more you notice that you can’t run quite as fast or lift just as much weight as you usually do, you’re likely flirting with overtraining and would benefit from a short de-load, McHale says. (This is where tracking all of your workouts comes in handy.)

Cut back on your exercise intensity, duration, frequency, or all three for at least one week. Then test yourself. Are your squats back on track? If so, proceed forward with your workout, making sure that, as you go, your performance has recovered. If not, give yourself some more time.

2. Your Muscles Are Super Sore

“Being sore for a couple of days after a super-tough workout is okay, but being achy all week long can point to pushing it too hard,” McHale says. “Soreness is a sign of muscular damage. It’s when your muscles repair themselves that you progress.”

So, if your legs are killing you, don’t be afraid to postpone a long run or leg day for once the soreness has let up. “Don't get caught up in thinking, ‘I have to do X, Y, or Z today because it’s on my schedule,” he says. “Put your ego aside.”

3. You've Discovered a Decrease in Heart Rate Variability

The differences in the amount of time between each and every heartbeat, heart rate variability (HRV) can give you valuable insights into your body’s stress levels and recovery status. Research consistently links decreased HRV to overreaching and overtraining.

To use HRV as a gauge of your exercise recovery, it’s important that you measure yours every morning (download ithlete or another HRV app to your phone) to establish a baseline. ithlete will display your HRV in green, white, amber, or red—all the way from “hit it hard” to “no gym today.”

4. Your Mood Sucks

Often, the first sign of overreaching doesn’t have anything to do with the gym. Rather, it comes out at home and work—through snippy comments, depressed thoughts, and a generally blue mood, Nelson says. Don’t dismiss mood disturbances lasting for a week or more, especially if they feel like they’re coming out of nowhere or occur in tandem with any of the other three signs here.

If you're feeling irritable, focus on doing things that help relieve any stress or tension you’re feeling. If exercise is go-to your main mood-booster, just opt for a less intense version. Try a long walk, leisurely bike ride, or restorative yoga class.

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