Week 5 - Locomotion 2 PDF

Locomotion II DR JON SHEMMELL MEDI258: HUMAN NEUROMECHANICS Learning objectives: Locomotion 2 u Kinetics of gait u Joint moments (torques) u Neural control of locomotion u Replicating human gait Kinetics of gait Kinetics of gait u External forces u gravity u fr...

Locomotion II DR JON SHEMMELL MEDI258: HUMAN NEUROMECHANICS Learning objectives: Locomotion 2 u Kinetics of gait u Joint moments (torques) u Neural control of locomotion u Replicating human gait Kinetics of gait Kinetics of gait u External forces u gravity u friction u ground reaction forces u Internal forces u muscles u friction Stance phase of walking modeled as an inverted pendulum High P.E. Low P.E. Low K.E. High K.E. u Forward momentum of the body provides angular rotation for rising phase of stance u Potential energy is transformed into kinetic energy during the falling phase u At toe-off, the axis of rotation is transferred from the ankle to the hip Potential energy (near Earth gravity) Ep (J) = mass (kg) x gravitational acc (m/s/s) x height (m) Kinetic energy (non-rotating mass) Ek (J) = ½ x mass (kg) x velocity (m/s)2 Swing phase of walking modeled as a conventional pendulum u The swing phase involves legs moving as conventional pendulums u Use of mechanical energy reduces the need for muscle activation u Potential energy at toe-off is converted to kinetic energy during the falling phase High P.E. of swing Low K.E. u The inverse occurs during the rising phase u Pendulum (leg) length accounts for the ”natural” frequency of human gait Low P.E. High K.E. Ground reaction force 1st half of loading response phase (Norkin & Levangie, 1992, p 476) 2nd half of loading response phase (Norkin & Levangie, 1992, p 476 1st part of terminal stance phase (Norkin & Levangie, 1992, p 477) 2nd part of Terminal stance phase (Norkin & Levangie, 1992, p 477) Ground reaction forces during walking Distributing ground reaction force u Pressure = Force/Area [N/m2] u Distributing force reduces the likelihood of injury u Centre of Pressure: “… the centre of the resultant forces.” (Richards et al., 2008, p 40) u Path of COP can reflect the efficiency of weight transfer and indicate potential for excessive tissue loading during gait Mechanical power during walking P(j) = M(j). w(j) (Watts) Positive joint power: concentric muscle action M(j) w(j) Energy (generation) >0 >0 Generation