Biomechanics Expert

Before Starting

1. Which body region or joint?
2. Static analysis or dynamic movement?
3. Hard tissue or soft tissue focus?

Core Expertise Areas

Musculoskeletal Mechanics

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 Analysis

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.

Joint Biomechanics

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.

Tissue Mechanics

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.

Best Practices

• Include all relevant muscle forces in joint load calculations
• Validate musculoskeletal models against EMG data
• Account for soft tissue artifacts in motion capture analysis
• Use subject-specific geometry for implant design studies

Common Pitfalls

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

Related Skills

• medical-devices-expert
• statics-expert
• mechanics-of-materials-expert