Let’s set the scene. You’ve had a good workout. Several, in fact. You’ve been going an extra mile on your run—just because, adding more weight to your leg press, or maybe you hit that 90-minute vinyasa class instead of your typical 60. Basically, you’re totally killing it and feeling great.

Until, one day, you wake up and feel, well… not-so-great. Your back is sore. Your neck is sore. Your quads are flaming. There’s a knot below your shoulder blade. And suddenly you feel like you can’t walk to the bathroom, let alone kick butt on your next workout.

What’s going on? Meet acute muscle tightness, or “delayed-onset muscle soreness” (DOMS), says Michael Jonesco, a sports medicine physician at The Ohio State University Wexner Medical Center.

Typically, DOMS is the musculoskeletal pain the creeps into your world about one to three days after particularly tough exercise, resulting in sore muscles, a loss of range of motion in your joints, and reduced muscle strength. (Ugh.)

Basically, tiny cellular changes are wreaking havoc on your body. “DOMS occurs when there is mechanical breakdown at the level of the muscle cell,” explains Jonesco. “This causes enzymes in the cell to recruit inflammatory mediators to the area, which stimulates pain receptors, called nociceptors, in the muscle cell.”

Experts aren’t sure why this breakdown happens, exactly. It’s a little bit mysterious and somewhat multifaceted. “There are several theories that exist to explain its origin, though no single theory has been accepted to date,” says Jonesco.

Don’t worry: there is no permanent damage to your muscles, and it turns out to be a win for your body in the end. “This is actually an adaptive process, which enables the muscle to strengthen and tolerate higher loads in future workouts,” Jonesco says.

Look for DOMS to pop up after you start a new strength program, “especially one heavy in eccentric activities, like exercises that strengthen the muscle as it lengthens it,” says Jonesco. For example, certain lunging activities for that target the hamstrings, and some yoga poses for the back. Symptoms are typically limited, and should improve over the next five to seven days.

During that period of soreness, your muscles won’t perform at the level you’re used to, which may increase the stress on your tendons and ligaments if you continue to OD on exercise. With that in mind, says Jonesco, you should back off on the intensity until you no longer feel sore and tight, or choose activities that don’t target the strained muscle groups.

The best treatment for reducing pain from DOMS, is actually more exercise, says Jonesco—just keep it light, and keep movin’. “Stretching and other flexibility training, like light yoga, can help to maintain joint range of motion. And massage and NSAIDs, like ibuprofen, can also aid in pain relief and muscle recovery,” he says. Ice can also help to manage pain and swelling, but it’s important to note that it won’t cut down the duration of pain—that’s just gotta run its course.

That other kind of muscle soreness—that “knot” in your back, or perhaps it’s in your neck, can also be exercise related, but it doesn’t have to be. Sometimes called “myofascial trigger points,” experts believe these develop when a certain muscle is tensed too many times, or for a long duration. This might be due to overuse during workouts, sitting too long, or even bad posture.

Science still hasn’t figured out exactly why muscles get “knots.” Since it’s rare to see a knot show up on a scan, some researchers are convinced they don’t actually exist—at least, not in the physical sense. In a paper published in the journal Rheumatology earlier this year, scientists suggest knots may actually be a neurological phenomenon caused by aggravated nerve endings.

How do you fix it then? The answer is usually massage—intense massage. Work it out with your hands, try unkinking it with a foam roller or therapy ball, or make an appointment for a sports massage. If those tricks don’t work, and the so-called knot persists, see your doctor or a physical therapist for more targeted treatment.

Bottom line: soreness usually works itself out in a matter of days. Just pay attention to your body to know when to lighten up (when you’re hurting) and when to amp it up (when you’re feeling strong again).