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Why your muscles get less sore the more you work out

Newbie exercisers often bond over the one thing they all have in common: the pain. Regardless of what sport you start with, you’re bound to suffer through a few aches as your body adjusts. But while it’s never fun to hurt, there’s a good reason for why and how it happens.

Some people wear their gym-induced soreness as a badge of pride. (“I’m sorry if I’m walking funny, I just squatted 350 pounds. Did I tell you I just squatted 350 pounds? Because I just came from the gym, where I squatted 350 pounds.”) And yet for others it’s just one more indignity they have to suffer through as their body adjusts to a new workout routine. (“Why am I walking funny? Because my spin teacher is a sadist, that’s why.”)

I still remember, with some fondness, the first time I got so sore it affected my life. After a tough leg day at the gym, I tried to lower myself onto the toilet and had to fall the last few inches after my quads just gave out. Getting “toilet sore” became a new goal of mine, because apparently I’m nuts.

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However you look at it, soreness is just a part of exercise. Science has good news, though: the post-workout pain lessens over time, until the only time you get really sore is if you try something new and difficult or make a big change to your routine. This is because our bodies are amazing, adaptable machines and part of why exercise is so beneficial, says a new study from Brigham Young University.

Researchers wanted to study what they call the “repeated bout effect,” or why exactly it is you’re less likely to get sore the more you exercise. Scientists have known for years that it has to do with the fact that exercise slightly injures your muscles, and as your body rebuilds them, they are remade to be stronger. (This is why you need to have rest periods between your workouts!)

But no one was sure exactly how this happened. To find out, they put 28 men and women through a super-intense workout and took muscle biopsies. And then they made the poor souls do it all again a few days later.

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They discovered something surprising in the overtaxed muscles the second time: T-cells. Yes, these are same kind your immune system sends out to fend off illness or infection. It turns out our bodies respond to strenuous exercise like they would to any type of inflammation, sending T-cells to heal the small tears in our inflamed muscles. But even cooler, these T-cells are quick learners and get better and faster at healing us the more times they have to do it.

“Many people think inflammation is a bad thing,” said lead author and grad student Michael Deyhle. “But our data suggest when inflammation is properly regulated, it is a normal and healthy process the body uses to heal itself.” This may also have something to do with why other studies have shown that regular fitness boosts your immune system, making you less likely to get sick.

And this is why you shouldn’t take pain meds before a workout, even if you’re worried it’s going to be a tough one, Deyhle added. Not only will they probably not help prevent soreness, they may actually hinder your muscles getting stronger.

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“Some people take anti-inflammatory drugs such as ibuprofen and aspirin after a workout, but our study shows it may not actually be effective,” he said. “The inflammation may not be directly causing the pain, since we see that muscle soreness is reduced concurrent with increases in inflammation.”

So, just remember this the next time you’re sweating through a grueling weightlifting session: Workouts cause pain, but it’s pain with a good purpose!

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