After running for 24 hours, elite runners have extremely high levels of a blood marker that signals their muscles are breaking down, and those levels stay high the next day.

After a tough leg workout, a blood marker of muscle damage (CK) spikes by more than 1.5 times and stays high for two days, showing the muscles are still healing.

After the second tough arm workout, blood markers of muscle damage tend to be lower, but the difference isn't strong enough to be sure it's real.

When healthy young men do a tough new workout that involves lowering weights slowly (like lowering a dumbbell), their muscles get sore and some blood markers go up, but within five days, everything goes back to normal—even if they’ve never done that workout before.

If you're a guy who lifts weights regularly, taking a specific supplement called HMB-FA about 30 minutes before a super tough workout might cut down muscle soreness and damage by nearly 70% compared to not taking it.

If you slow down the lowering part of weightlifting, your muscles might get more damaged and your body might release more of the hormones that help build muscle—this is what the claim says about guys who lift weights.