If exercise is a regular part of your healthy lifestyle, you’ve no doubt experienced muscle soreness before. But have you ever wondered why you feel sore after some workouts and not others? Or why it takes a couple of days for your soreness to kick in?

From weekend warriors to professional players, post-workout soreness—particularly delayed-onset muscle soreness—affects athletes of every level. Since soreness can either reflect changes in your workouts or indicate injury, though, it’s important to understand the science behind the phenomenon.

The Deal With Delayed-Onset Muscle Soreness

Soreness is a result of stress placed on muscles. When we stress our muscles during a workout, we create micro-tears in the tissues that are subsequently repaired. Eventually, this process makes our muscles stronger.

Typically, it takes the body 24 to 48 hours after a workout to produce the inflammatory response involved in this muscle tear-and-repair process. That’s why the sensation of soreness often occurs a day or two after a strenuous workout.

This time-delayed phenomenon has been termed “delayed onset muscle soreness,” or DOMS. Unenjoyable as it is, this process is essential for muscles to become stronger—and that delayed soreness indicates that your body is undergoing muscle repair (a good thing!).

Interestingly, some forms of exercise are more likely to induce DOMS than others.

Eccentric movements: Exercises that require controlled lengthening of the muscle (like lowering down from a pull-up) have been shown to be particularly powerful stimuli of muscle inflammation. (Yes, even more so than concentric exercises, like the first, upward half of that pull-up).

Read More: How To Use Eccentric Training To Get Stronger

New or more intense movements: Increasing the intensity of exercises you perform (like upping the weight of your squat) and introducing new exercises to your routine taxes your muscles to a greater extent than repeating a familiar workout.

When To Be Concerned About DOMS

While terms like “muscle damage” and “inflammation” have a negative connotation, these processes are essential for muscle growth, and some post-workout soreness is normal. However, there are a few red flags that could signal that your muscle soreness is actually an injury.

If soreness lasts more than a few days or is accompanied by bruising and/or swelling, consult with your physician.

Increasing your training intensity and duration haphazardly can set you up for overuse injuries like strains, sprains, or stress fractures.

How To Alleviate DOMS And Avoid Injury

You have to walk a fine line in order to optimally increase your training load without risking injury.

That’s why I recommend following the “10 percent rule” when adjusting your training. When increasing the intensity or duration of your workouts, make sure to only increase it by 10 percent per week.

When incorporating a new movement or type of exercise into your routine, make sure you fully understand the body mechanics behind the movement and pay close attention to form.

Read More: 8 Things To Do On An Active Recovery Day

To minimize the discomfort of DOMS, make sure you incorporate proper warm-ups and cool-downs into your routine. You can also support muscle recovery with devices like percussive therapy tools and compression boots, which increase blood and lymph flow while helping to remove metabolic waste that accumulates during muscle stress and repair. (If you don’t have access to these tools, foam rolling can also increase blood flow.) Finally, ice and Epsom salt soaks can also help decrease the inflammation associated with the muscle repair process. 

Outside of the gym, focus on staying hydrated, eating a healthy diet, and getting enough sleep; these factors are just as essential to muscle growth and recovery as your workouts. In fact, you produce as much as 75 percent of your human growth hormone, which helps repair muscles after exercise, during sleep. 

Dr. Brian J. Cole, M.D., M.B.A., is an orthopedic surgeon and Managing Partner at Midwest Orthopaedics at Rush in Chicago, Illinois. He is passionate about sports medicine research and is a renowned world leader in the field of cartilage restoration.