 For these peripheral elements to remain static, and not move unnecessarily, the spine, pelvis, and rib cage must be aligned towards this end.Thus the core muscles provide support of the axial skeleton (skull, spine, and tailbone) in an alignment where the upper body can provide a steady, solid base for the rifle to remain motionless.The nature of dynamic movement must take into account our skeletal structure (as a lever) in addition to the force of external resistance, and consequently incorporates a vastly different complex of muscles and joints versus a static position.