When is workout pain a red flag?

You are five minutes into your first run in weeks. The shortness of breath that you felt the first couple of blocks has dissipated. But then you feel a twinge in your knee stepping onto a curb.

Maybe you’re just rusty — or maybe it’s the beginning of a meniscus tear. Should you push through, or is your workout done?

Everyone’s perception of pain is different, but the choices you make in the moment — or the next day — can be the difference between a temporary nuisance and a persistent problem, said Beth Darnall, an expert in pain psychology at Stanford University and a former ultramarathoner.

“It actually might not have been a big deal, but suddenly we’ve created a big deal because we pushed through an additional five miles,” she said.

There are a few key signs to consider when you feel pain during exercise.

Was there a sound? If a sudden pain is accompanied by a crack or pop, you probably need to stop what you’re doing, said Mallory Fox, a movement specialist. Not every popping sound is a snapped ligament or tendon, but don’t take the chance.

Is it unstable or wobbly? Joints warrant special attention because they have more soft tissue that can cause persistent problems. If a joint won’t support your weight or feels like it’s buckling, it’s a strong sign that something is wrong.

Is it swollen? If you experience a lot of swelling within about 10 minutes, that’s usually a sign of a more serious injury, said Conor O’Donovan, a physical therapist.

Does the pain change how you move? Has your gait shifted or are you favoring one side? Even subtle changes can be a signal that it’s time to stop, Darnall said.

Is your range of motion affected? A healthy knee, for instance, should bend about 160 degrees, O’Donovan said, but a meniscus injury might cause it to catch a little or perhaps stop around 90 degrees.

How much pain do you feel, and what type? Broadly speaking, more serious injuries tend to cause sharp or throbbing pain, and a dull ache is more likely to be a temporary muscle issue, Fox said.

None of these rules are hard and fast, the experts said. Sometimes, the best approach is to wait and see how your pain changes. It sounds obvious, but pain should lessen over time, especially if you treat it.

“Having a sore foot right after you exercise is one thing,” Fox said. “But having that persistent pain for five days where nothing has helped” is a red flag.

That said, muscle soreness can flare up as much as a day later and last for a week. Such delayed pain may get worse for a couple of days, but it shouldn’t feel sharp and shouldn’t swell or limit your range of movement.

If you have persistent pain, you should follow your own comfort levels. It’s important to set goals and guardrails before exercising, Darnall said.

Whether you are running a 5K or just playing with your kids, plan out how often to take rests — and stick to them, even if you feel OK.

One way to know if you’ve pushed it too far is if you experience a “pain hangover,” Darnall added, which can cause trouble sleeping that night or limit your range of motion the next day.

But that’s not to say you should avoid working out. Exercise can be an excellent treatment for pain.

“It helps reduce stress, it helps you sleep better, it improves mood,” Darnall said. “You don’t want to do too much, but you also don’t want to stop.”