Expert-level biomechanics covering musculoskeletal mechanics, gait analysis, joint biomechanics, soft tissue mechanics, bone mechanics, and sports biomechanics.
Free body diagram: isolate body segment, include muscle forces and joint reactions. Muscle force estimation: redundant problem, optimization methods required. Moment arm: perpendicular distance from muscle line of action to joint center. Hill muscle model: contractile element, series elastic, parallel elastic components. Force-velocity relationship: muscle force decreases with increasing shortening velocity.
Gait cycle: heel strike to next heel strike, stance 60% and swing 40%. Ground reaction force: measured by force plate, three components. Joint moments: inverse dynamics from kinematics and GRF data. EMG: electromyography measures muscle activation timing and relative magnitude. Kinematics: motion capture tracks marker positions, derives joint angles.
Knee: tibiofemoral and patellofemoral joints, cruciate and collateral ligaments. Hip: ball and socket, high contact forces, cup and stem in total hip replacement. Spine: intervertebral disc mechanics, facet joint loading, core muscle stabilization. Shoulder: glenohumeral instability, rotator cuff muscle coordination.
Bone: cortical and cancellous, anisotropic, viscoelastic, fracture mechanics. Cartilage: biphasic theory, fluid pressurization carries load acutely. Ligament and tendon: nonlinear stress-strain, toe region then linear region. Muscle: active and passive forces, fiber architecture determines function.
| Pitfall | Fix |
|---|---|
| Ignoring muscle co-contraction | Antagonist muscles increase joint loading |
| Static analysis for dynamic activities | Use inverse dynamics for running and jumping |
| Wrong joint center location | Small errors propagate to large moment errors |
| Assuming rigid bone | Include deformation for fracture risk studies |