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All about muscle soreness

Why do our muscles get sore? How can we treat muscle soreness? Do I have to get sore from my workout to get stronger?

Dawson Persons

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Our members often ask us about muscle soreness, both what causes it and what can be done to treat it. In this blog, our goal is to give an overview of both of these questions.

But first, a disclaimer.

The cause of muscle soreness is still debated within the field of exercise physiology. Over the years, multiple theories have been suggested, tested, and even debunked. In no way are we able to say with certainty what scientists themselves cannot. Our goal is simply to give an overview of the current opinions.

Links to more in-depth explanations are also provided below.

The cause of muscle soreness

As stated above, the cause of muscle soreness is still debated, and you can find respected individuals and institutions holding opposing views. In fact, two of the videos provided below will disagree with one another on the exact cause - but both will admit that there is likely more than one factor involved.

It is also helpful to understand that not all muscle soreness is the same. There are two main types that our members typically experience:

  • Acute Muscle Soreness

  • Delayed Onset Muscle Soreness (DOMS)

Acute muscle soreness

Acute muscle soreness is the feeling you get while you’re exercising, or right after, and it usually goes away pretty quickly.

For example, think about the burning feeling in your thighs during a wall sit or a sled push. That’s acute muscle soreness.

What’s happening is pretty simple: when a muscle is working hard for a long period of time, it doesn’t get as much blood flow as it normally would. Because of that, certain byproducts build up in the muscle, which creates that burning sensation you feel.

When blood flow returns after the exercise ends, those byproducts are “flushed” out of the muscle.

Delayed onset muscle soreness (DOMS)

DOMS is the soreness you feel a day or two after a tough workout.

For example, you might squat on Monday, feel fine on Tuesday, and then wake up Wednesday with sore legs.

Researchers now agree on one important thing: DOMS is not caused by lactic acid buildup. Lactic acid levels return to normal fairly quickly after exercise - long before that soreness shows up - so it’s not the reason you’re sore later.

So what does cause it?

There are a couple of leading ideas, and they actually work well together:

  • Small muscle damage: When you do something new or especially challenging, your muscles experience tiny amounts of damage (often called “microtears”). This is a normal part of getting stronger, but it can make the area feel sore as it repairs.

  • Inflammation and swelling: Your body responds to that damage by sending in immune cells to help repair the muscle. This process can lead to swelling inside the muscle, which creates pressure and contributes to soreness.

This second idea helps explain the delay because that repair and inflammation process takes time to build, which is why you don’t feel it right away.

The bottom line is that DOMS is most likely caused by a combination of muscle damage and your body’s repair response, not lactic acid.

What should you do about it?

So that’s what causes muscle soreness, but what should you do when it happens?

For acute muscle soreness, the answer is simple: finish the exercise, and that burning feeling will go away pretty quickly.

For DOMS, the approach is also straightforward. The goal is to keep blood flowing to the sore muscles so your body can recover.

One of the best ways to do that is to keep moving. Low-intensity activity like going for a walk or doing light exercises helps increase blood flow without adding extra stress to the muscle or slowing down recovery.

Other recovery methods like massage, sauna, or cold plunges might help you feel better, but their physical impact on recovery is likely small. They can still be useful if they help you relax or stay consistent.

So the next time you’re sore from a new workout or phase, the best thing you can do is to continue moving.

If you're interested in learning more, check out these video explanations: What Is Muscle Soreness? It Isn't Muscle Tears... | Dr. Andy Galpin & Dr. Andrew Huberman 

(3) Causes of Muscle Soreness - Coursera Science of Exercise - YouTube 

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