This chapter deals with occupational biomechanics and the forces acting on the human body. There is a detailed introduction to spine anatomy and biomechanics including spinal compression forces and tolerance limits, back pain and checklists for initial assessment of demanding tasks. There is also a detailed discussion of posture and the functional anatomy of heavy work. Biomechanical risk factors for musculoskeletal injury and back pain are identified with guidance to eliminate them in the design. Readers are introduced to equations derived from Newton's Laws of Motion to calculate spinal compression forces and G forces resulting from falls and collisions, with worked examples.