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Lecture 8

KIN 427 Lecture 8.docx

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KIN 427
Stuart Mc Gill

KIN 427- Lecture 8- January 31, 2013 Contention issue - injury from bending down to pick up pencil (ie. sneezing, or just bending down to stroke cat) - you have to be an advocate→ lot of times these people are denied compensation * - very best for lifting→ keep spine in neutral position and only hip hinge - 2nd best- hip hoique spine is not moving (locked in flexed position) -3rd - Olympic lifters etc don't end career with bad back, instead with shoulder or knee injuries Mechanism- back buckling- @L4/L5- stability - spine stability- mast rigging Stability : a qualitative example - stability depends on geometry , stiffness *, balance "cable tensions" and column :imperfections" - L spine buckles with 90N(20 lbs) - don't have to put a lot of tension in the robes, but key is to be putting symmetric tension in each rope - mode of bucking→ determined by the stiffness around the spine (buckling goes the one that is less) - guy wires→ more stability if the belly is more away from spine→ to optimize stability Stability: - PE- 1/2 * K* x^2 - S: PE-P - S<1: unstable - S>1: stable - ie. raising arm→ did work to store energy (PE) - one spine vertebra→ 2 guy wires on either side,these act as springs, modulating stiffness (playing with K), right motor control and tune the muscles (PE) - tune amount of activation of guy wires= stiffness= increase PE P ↓ k - get it to have high potential energy- but can't put it on the whole day (can't be stiff the whole day- it's about tuning- controlled tuning)→ tune stiffness so they can survive P of the sneeze - at low levels of activation and high levels of activation is where instability occurs - whole abdominal wall and diaphragm helps with stiffness Muscle function and stability 1) muscle stiffness is always stabilizing 2) muscle force may stabilize or compromise stability.... too much of too little - thus risk is at very low levels and high levels of activation - forces run beyond the stiffness (stiffness always stabilizes, forces may or may not stabilize) Stability and fixation - "punctum fixum": the core must be stiffened and "fixed" to provide the hip musculature a stiffened mass to piss from - proximal stiffness creates distal mobility (power on other side of ball and socket joint
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