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.

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.

If young men who haven't exercised before do either multi-joint exercises (like pull-ups) or single-joint exercises (like bicep curls) for 10 weeks, their arm strength increases by about the same amount - neither type of exercise is clearly better than the other.