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Clinical Biomechanics in Health and Injury

Clinical Biomechanics in Health and Injury


  • Deconstructing mechanism of injury

    • Clinical objective: deconstruct mechanism of injury to identify injured tissue(s)

    • Systematic analysis of biomechanical forces/anatomic structures involved.

    • Holistic view: examine full kinetic chain, interaction of different joints.

    • Informs treatment: targeted intervention based on the mechanism of injury/tissues involved.

  • Kinematics vs Kinetics

    • Kinematics: 

      • Study of motion description (quality) without regard to its cause (ie., forces).

      • Describes the linear and angular position and motion (displacement, velocity, acceleration)

    • Kinetics:

      • The study of bodies in motion with respect to the characteristics of forces acting upon them.

        • Magnitude and location

        • Location and direction

        • Duration and frequency

        • Rate of application

      • Forces can be active or passive

        • Active = contractile tissues (actin-myosin)

        • Passive = non-contractile tissues (elastic potential energy)

  • Concentric vs Eccentric Contraction

  • Newton’s First Law of Motion

    • “A body at rest or in uniform motion (velocity) (linear, angular) will remain so unless acted upon by a net external force.”

  • Newton’s Second Law of Motion

    • “A force (N) acting on a mass (kg) will cause an acceleration (a) (linear, angular) that is proportional to the Force.”

    • F=ma

  • Newton’s Third Law of Motion

    • “For every action, there is an equal and opposite reaction.”

  • Centre of Mass (~COG)

    • COM: ‘point mass’ that behaves like the distributed mass.

    • WHY use COM? - Facilitate mathematical analysis of biomechanical systems.

  • Is the COM always inside the body?

  • Is the COM a fixed point?

  • What factors affect COM in humans?

  • What are the implications to injury?

  • Moment of Force (Nm)

  • Moment of Inertia

    • Greater resistance (r -> 2r

    • Taller people are more likely to get injured.





  • What is the Moment of Inertia for the segment?

    • Don’t know where the centre of mass is, only know length.

    • Not the length of the segment, it is the centre of mass.









  • Angular velocity and Centrifugal Force

    • M = mass

    • W = angular velocity

    • R = radius

      • Vt = Linear Velocity (Measurement of Time)

      • Fc = Centrifugal Force (N)

      • Ac = Centrifugal Acceleration (Measurement of Time)











Clinical Applications of Moments


  • What are the Implications of Moments of Force to back pain/injury?

    • Creates Hyper Lordosis (spine)

    • Compresses spine











  • Clinical Considerations of Moments in the Hip Joint

  • Clinical Applications of moments of inertia

    • ‘Proper lifting techniques

    • Keep objet close to your body

    • “Hug and lift”







  • Clinical Applications of moment of inertia:

    • Compressive forces in the low back during lifting.






  • Who is more predisposed to developing back pain? A: Right guy

  • Athletes have experienced disc herniations……

  • Why are golfers and tennis players predisposed to developing back pain?


  • Moment of Inertia: applications in sprinting

  • Female versus Male hip Q-angle

  • Shoulder abduction: rotator cuff injury

  • Angular velocity and Radial Acceleration - injury implications?