A chin up is a variant of a pull up where your forearms are supinated, allowing you to grab the bar with an undergrip. The main muscle working here is still the latissimus dorsi, and it's still a compound exercise which uses a lot of helper muscles, but there are two key differences. Firstly, in a chin up, your biceps and brachialis are perfectly aligned with the line of grip tension, which allows them to engage really hard and help the movement. Secondly, because the elbows are in front of your

Have you ever wanted to see what the inside of your arm actually looks like? This is it — layer by layer. Beneath the skin lies a precisely organized system of fascia, muscle bellies, tendons, nerves, and vasculature — all working in perfect coordination every time you grip, lift, rotate, or throw. The forearm alone contains over 20 muscles divided into flexor and extensor compartments, all controlled by branches of the median, ulnar, and radial nerves. Most people never think about what's happe