Some guys who do really intense bicep exercises can lose almost all their strength right after and take over a month and a half to fully recover — way longer than usual.

Doing certain types of hard arm exercises that lengthen the muscle while it's working can make your arms weaker and less flexible within a day.

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.

After a tough bicep workout, guys' arm muscles swell up a lot in just two days, then shrink below normal size and stay that way for over two months.

If healthy guys train one arm with heavy weights three times a week for three months—whether they push to total muscle exhaustion or not—they’ll get stronger, their muscles will grow, and their brains will activate those muscles better.

When young men who haven't trained before do either multi-joint exercises (like curls) or single-joint exercises (like bicep curls) for 10 weeks, their arm muscles grow by about the same amount - there's no meaningful difference between the two types of workouts.