Anatomical and Biomechanical Foundations
This domain tests how the exam expects you to describe human movement with mechanics: planes and axes, joint motion, force, torque, levers, and tissue response. Expect calculation-style items and applied questions that ask why a load feels harder at one joint angle.
Core rules
- Motion occurs in a plane about a perpendicular axis: sagittal/flexion-extension about a frontal axis; frontal/abduction-adduction about a sagittal axis; transverse/rotation about a vertical axis.
- Kinematics describes displacement, velocity, and acceleration; kinetics explains forces and torques.
- Newton I: no acceleration without net force; II: F = ma; III: equal and opposite reaction.
- Torque = force × perpendicular moment arm. A longer moment arm increases torque for the same force.
- Levers: first class (balanced), second (load between fulcrum and effort), third (effort between fulcrum and load; most limbs).
- Bone is viscoelastic: response depends on load magnitude and rate; stress = force/area, strain = deformation/length.
Worked example
A 10 kg dumbbell is held with a horizontal moment arm of 0.30 m from the elbow. Load force = 10 × 9.81 = 98.1 N. Elbow torque = 98.1 × 0.30 = 29.4 Nm. If the moment arm shortens to 0.15 m, torque halves to 14.7 Nm, so the flexors need less torque-though other factors such as muscle length and velocity also change.
Traps
- Swapping plane and axis.
- Using total limb length when only the perpendicular distance creates torque.
- Treating force and torque as interchangeable.
- Forgetting forearm/hand segment weight in a torque estimate.