Coach Mark Rippetoe introduces the basics of muscle action.
Understanding how a muscle works is essential to understanding how to strengthen it. This footage is taken from his Basic Barbell Certification seminar at CrossFit Brand X in Ramona, CA on February 14, 2009.
This video covers the most basic concepts, such as flexion and extension, concentric, eccentric and isometric.
As simple as the concepts may be, a lot of very intelligent people still squat predominantly with their quads instead of their glutes and hamstrings. Coach Rippetoe orients his teaching of anatomy and physiology toward achieving proper mechanics in the basic barbell exercises.