Peter Roberts's video: The Key Detail Everyone Forgets with Biceps Curls and Triceps Extensions

Biceps and triceps exercises service an obvious function: to isolate and train the bis and tris. This is something you might want to do this for performance reasons or for aesthetic reasons. Whatever the purpose, remember that these exercises are also an opportunity to practice great shoulder control. One of our basic principles is to keep the shoulder in a 'centered' position in the joint, yet in many biceps and triceps exercises it's easy for the shoulder to hike up or translate forward. Both errors are bad habits that can pop up in a wide variety of upper body movements and lead to i) decreased performance and ii) an elevated risk of shoulder injury. Whether it's a relatively straight forward one-joint exercise like a biceps curl or something more complex like a bench press or pull-up, make sure you're practicing the right movement pattern.