Guys who work out regularly might only start showing signs of muscle damage after the third month of a strength training plan, possibly because the workouts get too intense or they’re not recovering enough.

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.

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.

When rats do low-frequency weightlifting, their blood doesn't show signs of muscle soreness or energy stress, meaning this kind of exercise doesn't hurt or tire their muscles.

When rats do resistance exercises less often, their blood doesn't show signs of muscle damage or stress—so this kind of workout seems gentle on their bodies.

After really intense muscle workouts, healthy guys can have super high levels of a muscle enzyme in their blood—way above normal—peaking a few days later, which shows their muscles are breaking down a bit, but their kidneys are still fine.