This unit starts by explaining overarching ideas of why a familiarity with basic sciences is important to a professional barbell coach, but at the same time how getting lost in the minutiae is a pitfall that should be avoided. After this, we go over muscle structure from the level of a muscle down to the smallest contractile unit, the sarcomere. Once there, the sliding filament model of muscle contraction is introduced. Finally, we discuss how the physical configuration of the sarcomere is a constraint on its ability to produce force.