When young male rugby players switch from heavy lifting to doing more reps with lighter weights, they feel more muscle soreness and show signs of more muscle damage in blood tests.

When young male rugby players switch from heavy strength training to a higher-rep, lighter-weight muscle-building routine, they feel more sore and show more signs of muscle damage in their blood tests.

Just because your muscles aren’t sore or your blood doesn’t show damage markers doesn’t mean you’re not getting stronger—your body can adapt without those signs.

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.

When young guys do a tough arm workout a second time, their muscles aren't as sore, swollen, or damaged as they were the first time — their bodies seem to adapt after the first go-around.

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.