structure of biological materials - ece.mcmaster.ca
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3. BIOMECHANICS
Some areas of biomechanics research and application: – movement and locomotion mechanics – tissue mechanics – orthopaedic prostheses & implants – impact mechanics – neuromuscular control – functional electrical stimulation – cell mechanics and locomotion
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3.1 Locomotion
Quantifying the mechanics of human locomotion will be helpful in:
– developing mathematical models of biomechanical systems,
– understanding the effects of pathology or injury on locomotion, and
– determining the important properties required for orthopaedic prostheses & implants, functional electrical stimulation, etc. to restore near-normal locomotion
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Determining kinematics from the GRF
Acceleration of the center of mass (C.O.M.):
where Fgz(t) and Fgy(t) are the vertical and horizontal components of the ground reaction force (N), m is body mass (kg), g is acceleration due to gravity (ms-2), and az(t) and ay(t) are the vertical and horizontal acceleration of the C.O.M. (ms-2).
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Velocity of the C.O.M.: where vz(t) and vy(t) are the vertical and horizontal velocity of the C.O.M. (ms-2).
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Total mechanical energy of the C.O.M.: where Ekin(t) is the kinetic energy of the C.O.M. (J):
and Egrav(t) is the potential gravitational energy of the C.O.M. (J):
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Models for walking & running: walking ¼ kinetic energy ) inverted pendulum gravitational potential energy ) kinetic energy running ¼ kinetic energy & spring-mass system gravitational potential energy ) elastic potential energy ) kinetic energy & gravitational potential energy
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Implications for orthopaedic prostheses & implants, functional electrical stimulation (FES), etc.
Walking: – optimal walking speed is »1.25 ms-1 for
adults, because the exchange of gravitational potential energy with kinetic energy is most efficient at this speed
– at walking speeds >1.5 ms-1, fluctuations in kinetic energy greater than fluctuations in gravitational potential energy
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Walking (cont.): – at walking speeds <1.0 ms-1, fluctuations in
kinetic energy less than fluctuations in gravitational potential energy
Consequently, to restore a near-normal walking motion with optimal efficiency, we need to obtain:
– a natural pendular motion, and
– a walking speed of between 1.0 and 1.5 ms-1.