After doing a hard arm workout twice, four weeks apart, people feel stronger sooner the second time—even though they did the same amount of work.

People push just as hard during the second workout as the first, even though they feel less sore and recover faster.

When people who don't normally lift weights do a tough arm exercise twice, four weeks apart, their biceps don't stretch as much the second time, even though they're trying just as hard.

When you bend your elbow by lifting something, the brachioradialis muscle works much harder pushing up than it does lowering the weight slowly.

How much your biceps stretch during your first hard workout tells you how sore and weak you’ll feel the next day—but not how much enzyme leaks into your blood.

If you're new to lifting weights, doing exercises where you lower the weight slowly (eccentric) might make your biceps grow bigger than exercises where you lift the weight up (concentric), after 8 weeks of training.