No pain, no gain?

Kiana Schulze
Jul 29
7 min read

Writer: Kiana Schulze, PhD

Editors: Jackie Nguyen, Michaela Murphy, Rachel Buckley

Illustrator: Jackie Nguyen

This is not medical advice. Consult a healthcare provider before starting or changing an exercise routine. Every individual is different, so it is important to work with a professional and listen to your body to prevent injury.

You finally gave in and joined your friend who’s been nagging you to attend 5am-mega-reformer-hot-pilates-extreme-super-challenge class with her, and now you’ve been greeted by limbs that feel like Jell-O. This feeling is generally referred to as muscle soreness. More specifically, scientists call it delayed onset muscle soreness, or DOMS, because it commonly doesn’t appear until 12-72 hours after a bout of physical activity. It can even last for 5-7 days, so it might give you an excuse to skip that next workout class and then conveniently forget about them altogether.

DOMS is most often associated with new movements or eccentric exercises – exercises where the muscle lengthens during contraction, such as downhill walking, or during the lowering phase of a squat, pull up, or bicep curl. But, new movements are not limited to weightlifting. Remember that time you tried to do a cartwheel 20 years after your last gymnastics meet, or helped your buddy move their unnecessarily large couch (seriously, a studio apartment does not need THAT big of a sectional)? Manual labor, hobbies, and sports can all lead to DOMS because they challenge your muscles in new ways.

So, what really happens when we exercise?

When muscles are worked, particularly with resistance (such as during weightlifting), tiny tears are created in the muscle. These are not injuries, like a pulled muscle, which is a larger, more severe tear of muscle fibers, but just small bits of damage. These micro-tears are repaired by adding new proteins to reinforce the muscle and, with each repair, the muscle grows a little bit stronger. That way, it is better equipped to handle resistance when it encounters it again.

In strength training, this concept is known as “progressive overload” — gradually increasing the weight, repetitions, or time under tension (by slowing down the movement) to encourage the muscle to adapt. Thus, the same weight and reps that challenged you last week may feel easier today. Progressive overload is fundamental for longevity. By steadily building strength, you increase bone density, protect your tendons and ligaments, and support your body, which is especially important as we age.

Imagine a bridge. At first, the bridge might not get much traffic, so it can handle the few cars driving across. Over time, more cars begin to take the bridge route, increasing the load. Small cracks appear, so construction crews repair and reinforce it. Now, the bridge is stronger. Creating new cracks would now require more load, like a bunch of semi-trucks. The bridge (our muscle) is prepared to handle more next time because it has been adequately reinforced (muscle recovery) from the incremental increases in load. However, if semi-trucks drove over the original bridge or over the reinforced one before the construction crews were done, it might collapse. The same is true for muscles: adding too much load or activity too quickly increases the risk of sprains, strains, and overuse injuries.

Now, you may be thinking: “Okay, so the tiny tears are what make me feel sore!” Unfortunately, it’s much more complex than that: you can still build muscle and strength even if you don’t feel sore after exercise. Soreness can follow a tough workout, but it is not required for progress. So, if it isn’t as simple as tear-and-repair, what’s the culprit for DOMS?

What causes DOMS? (and why it is not lactic acid)

You may have heard from your high school coach or online “fit-fluencers” that lactic acid is the cause for DOMS. Lactic acid is often vilified as the ‘toxic waste’ blamed for the burning sensation during exercise, and the muscle aches that occur later. For many years, scientists did believe that lactic acid caused DOMS, but this theory has since been debunked. But what is lactic acid anyway?

For muscles to contract, they require an energy source. Processing energy creates many biological byproducts, one of which is ‘lactic acid,’ or lactate combined with a hydrogen ion. This hydrogen ion creates a more acidic pH in the muscle which is to blame for the burning sensation during exercise but not for DOMS. To get rid of this hydrogen ion and restore normal pH, our bodies send it through a chemical reaction to create water and carbon dioxide, which we exhale. This happens so quickly that ‘lactic acid’ doesn’t really stick around for long, and we are left with just lactate.

Contrary to popular opinion, lactate serves many beneficial purposes in the body. For example, it’s a great energy source for the brain and the heart, providing the fuel for you to think and for your heart to pump >100,000 times each day! It can also be shuttled throughout the body, so it doesn’t “build up” in the muscle as previously believed. The misinterpretation that lactic acid is the source of our pain was largely due to observations that lactate rises during exercise. It’s true that blood lactate levels increase with many forms of exercise, but it’s important to note that blood lactate also rises during forms of exercise that are less associated with DOMS, including concentric (muscle shortening) exercises and high-intensity aerobic exercise. There is actually no observed correlation between measured lactate levels and muscle soreness. Additionally, lactate levels typically return to pre-exercise levels within 1 hour post-exercise, meaning that lactic acid, or lactate, is highly unlikely to be the cause of soreness that occurs days later.

So, what does cause DOMS? At this point, we still can’t say for sure. Scientists have proposed several theories including muscle spasm, muscle damage, inflammation, or connective tissue irritation. Most scientists now think that DOMS is due to some combination of these processes rather than a single cause.

Is DOMS good or bad?

Some people feel like they didn’t work out hard enough if they aren’t sore the next day. As mentioned above, soreness is not the only indicator of a good workout. As your muscles and nervous system adapt, you’ll likely feel less sore each time. The best indicator that your fitness is progressing is simply whether you can do more over time. Can you run farther or faster? Can you lift the same weight for more repetitions, or lift a heavier weight? Keeping track of your physical abilities and how you feel during exercise is a much better metric than soreness to determine whether you’re adapting and getting stronger.

Others fear DOMS will interfere with staying active throughout the week or that it signals something harmful to their muscles. If you can’t tell whether you’re injured or sore, notice whether the pain is dull and generalized across the muscle (sore), or sharp and localized to a specific point (injury). Soreness will peak within 1-3 days then fade and will ease as you move around, whereas the pain of an injury will often worsen when that body part bears weight. Although DOMS may be a slight hinderance, it is likely to appear if you begin a new training program or mix up your routine. That soreness is simply a sign that your muscles are experiencing a new type of stress and may need a few days to recover before they are ready to be worked again.

If you haven’t felt sore in a while and you want to, you can consider trying a new activity or spending more time during the eccentric part of exercise. For example, move slower on the lowering phase of your exercise, like a squat or a push up, to increase time under tension. Slowing down increases the time the muscle is working, which increases mechanical stress. Just remember to start with a lower weight than usual, if using weights, since slowing the exercise increases load on the muscle.

If you are worried about DOMS disrupting your training schedule, there are ways to minimize the discomfort of DOMS. Warming up thoroughly, specifically with the movements you plan to do in your workout, along with dynamic stretching and walking can help prevent DOMS. Dynamic stretches are controlled movements though your range of motion, like arm circles or body weight lunges. In addition to potentially reducing DOMS, proper warmups are also important to reduce your risk of injury, similar to how warming up a rubber band makes it less likely to snap.

Once soreness sets in, the best way to ease DOMS is through light active recovery, such as gentle yoga, walking, or easy cycling or swimming. Active recovery increases muscle blood flow, which delivers nutrients for repair and takes away inflammatory molecules. Some studies suggest that massage (or foam rolling) is effective, or that cold or heat therapy can help. These strategies appear to be effective on a more person-dependent basis compared with active recovery. In fact, cold therapy can even blunt your gains because it slows protein synthesis, a key part of muscle repair and growth, so don’t feel bad if you want to skip the ice bath. Of course, getting adequate sleep is also important for allowing your body to recover.

Another way to support your body as it recovers from activity is through proper nutrition and hydration. Nutrient needs are incredibly individualized, but refueling with protein and carbohydrates from whole foods generally provides the nutrients and energy your muscles need for repair. Maintaining good hydration status throughout the day by regularly sipping water is always important, but it can also help you recover. Our bodies are made up of water, after all!

Although DOMS isn’t the same as an injury, you should remain cautious about jumping back too quickly into working the sore muscle group again because DOMS may impact movement patterns or force output. DOMS can increase your likelihood of getting injured because you might compensate with other muscles during exercise or even daily movement, leading to poor form. Consider a time when perhaps you walked up the stairs a little lopsided after leg day. This shift in your normal walking pattern has the potential to place undue stress elsewhere, like your hips and back. Maybe you even skipped the stairs completely and took the elevator because of how hard stairs were that day. Taking the elevator in this case is evidence of how DOMS impacts force output and is a great way to adjust your load with a more severe case of DOMS. It’s important to protect your body by adjusting loads and workouts as needed to allow your muscles time to repair and avoid injuries associated with overuse.

The bridge from science to strength

While DOMS can be uncomfortable, it shouldn’t deter you from trying new forms of exercise! In fact, adding variety to your workout routine can keep you motivated, help you build and maintain well-rounded whole-body strength, and can actually extend your lifespan. Just remember that allowing your body time to recover using gentle movement, rest days, good nutrition, and sleep is key to preventing injuries. Most importantly, the benefits of regular exercise far outweigh the negatives associated with the occasional DOMS, but that’s a topic for another day…stay tuned!