On February 17th, 2016 we learned about

Immune system’s cells found to play a role in muscle repair

We all know that exercise is good for your health, but it’s still pretty surprising to find out that your immune system plays a direct role in muscle building. This isn’t to say that hitting the weights is causing some kind of infection, but it researchers have discovered that T-cells, a key component in your immune system’s defenses, are very active in exercised muscle tissue. They may even be the reason that your second trip to the gym feels easier than the first.

Tears and repairs

When you really work your muscles, such as when lifting weights, you’re actually damaging them. The muscles suffer a series of small tears, which then trigger specialized cells to come in and repair the damage. These satellite cells repair the damage by moving into the new gaps, dividing and replicating until the tear is rejoined. In doing so, the overall amount of muscle tissue is actually increased, which allows the muscle to complete a similar amount of work in the future without needing to tear, essentially boosting your strength.

In a multi-day workout routine, you might feel sore afterwards, but less sore the next time around. This phenomenon, called the repeated-bout effect, isn’t just because those satellite cells have beefed up your bod already.  It’s actually been a complex and open question for some time, with your immune system’s T-cells being the latest factor found playing a role in muscle-building. Since T-cells normally help fight infections from bacteria and viruses, it was only after they were seen in healthy mouse muscles that scientists even thought to look for them in humans after a good workout.

Patched muscles and puffiness

Interestingly, the T-cells may still be following their usual functionality in these healthy muscles. Just as your immune system learns the signature of dangerous viruses or bacteria in order to respond more quickly to them, your torn muscles seem to recruit T-cells to tears faster after subsequent workouts. The T-cells then arrive and seem to trigger a small amount of inflammation, which may be accelerating the muscle’s repair. If that is the key mechanism in this system, it may be the source of the repeated-bout effect— your follow-up workouts feel easier because the T-cells get started on their work faster.

This isn’t completely conclusive at this point, but its opening up new questions about the role of inflammation in muscle building, suggesting that we may not fully appreciate how it helps our body restore itself.

Source: Why your muscles get less sore as you stick with your gym routine by Todd Hollingshead, ScienMag

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