Anatomy, Physiology, and Biomechanics
What is tested
This domain checks whether you can name a structure and then use it: predict the joint glide, the muscle length at which force fails, or the gait phase where a load appears. Expect mixed recall-plus-application items rather than simple labelling.
Core rules
- Convex–concave rule. Convex moving surface: roll and glide are opposite. Concave moving surface: roll and glide are the same. Glenohumeral abduction: the head rolls superiorly and glides inferiorly.
- Scapulohumeral rhythm. About 2:1 - roughly 120° glenohumeral and 60° scapulothoracic across 180° of elevation.
- Levers. Plantarflexion at push-off is a second-class lever: fulcrum at the metatarsal heads, effort at the triceps surae, load is body weight.
- Two-joint muscles. Active insufficiency occurs when the muscle is shortened, e.g. hamstrings with hip extension plus knee flexion. Passive insufficiency occurs when it is lengthened, e.g. hamstrings limiting straight leg raise.
- Force–velocity. Eccentric force exceeds isometric, which exceeds concentric; concentric force falls as velocity rises.
- Gait. Stance is about 60%, swing about 40%, double support about 20% of the cycle; comfortable velocity is 1.2–1.4 m/s.
- Physiology. Calcium binds troponin C, tropomyosin shifts, and actin–myosin crossbridges cycle using ATP. Motor units are recruited by the Henneman size principle.
Worked example
A patient seated with the hip flexed to 90° cannot actively extend the knee past about 30° of flexion; standing, extension is full. Reasoning: seated, the hamstrings are pre-shortened at the hip, so the same muscle cannot generate enough tension to extend the knee - active insufficiency of a two-joint muscle. Standing with the hip extended, the hamstrings are lengthened and knee extension is full. This is not quadriceps weakness; test quadriceps in a position where the hamstrings are not pre-shortened.
Traps
Mixing osteokinematic (bone) and arthrokinematic (joint surface) terms; memorising the convex rule backwards; forgetting the scapula contributes 60°; assuming a weak movement is always the prime mover's fault.