WASHINGTON - Flex your arm. You already know which muscle you're showing off. The biceps are among the most recognizable muscles in the human body, but they share the upper arm with a less-celebrated ...

Beth Skwarecki is Lifehacker’s Senior Health Editor, and holds certifications as a personal trainer and weightlifting coach. She has been writing about health for over 10 years. Arm day can be one of ...

Many lifters fall into the trap of "mirror training," obsessively hammering biceps, chest, and abs because those are the muscles they see every day. However, if you want truly impressive arms, you ...