Muscle and Motion on Instagram: "Bicep Curls: Flexed vs. Extended Shoulders 🔥 Ever noticed how bicep curls are a gym staple? You'll always find someone curling away! Let's dive into the biomechanics of bicep curls and see how shoulder positioning -- flexed or extended -- affects the biceps' different heads. 🌟 Flexed Shoulder Position: When your arm is in shoulder flexion during the curl, it slightly shortens the biceps brachii's long head, putting more work on the short head and the brachialis