Biomechanics Intro

What is Biomechanics?

Biomechanics: the study of forces & their effects on living things

3 Branches of Mechanics

• Statics

  • physical system does not experience any change in motion (ergonomics, posture, etc)

• Dynamics

  • physical system does experience change in motion (sprinting, sitting → standing, etc)

• Fluids

  • gasses/liquids

  • pressure, volume, density, viscosity (CV system, aerodynamics)

• Kinematics

  • things we can see

  • (is it moving? is it getting faster/slower?)

• Kinetics

  • things we can’t see that explain why things move

  • (why is/isn’t moving? why is it getting faster/slower?)

Gait Metrics, Energy, Work, & Power

• Spatial: where things are in space

• Temporal: when things happen across time

• Linear: motion occurring in a line

• Angular: motion around an axis

Work = ∆Energy = Energy_final - Energy_initial OR Work = force x displacement

Power = work/time = force x velocity

• Energy = capacity to do work (joules or kilocalories)

• Work = change in energy of a system (joules)

• Power = rate at which work is performed (watts = joules/ sec)

Forms of Energy

• In human movement: kinetic vs potential (stored/gravitational/elastic/chemical,) always changing % kinetic vs potential

Tissue Mechanics

Different tissues exhibit different mechanical & physical properties which effect how they behave

• tendon

• ligament

• bone

• cartilage

• muscle*

Properties change with injury/pathology/time

• Tendon, ligament, bone, & cartilage experience loading & unloading of force, we use stress & strain to study behavior during loading & unloading

• Stress: related to force

• Strain: related to length change

• Muscle is different

  • muscle can contract to produce force, we can study the things that effect its ability to do so

    • motor unit recruitment

    • rate coding/firing frequency

    • muscle architecture

    • length-tension relationship

    • force-velocity relationship