Transcript Moment Power Analysis - University of Ottawa

Moment Power Analysis and
Absolute Power Method
D. Gordon E. Robertson, PhD, FCSB
Biomechanics Laboratory,
School of Human Kinetics,
University of Ottawa, Ottawa, Canada
Biomechanics Lab., University of Ottawa
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Inverse Dynamics Review
• divide body into kinematic chains
• divide chains into segments
• from free-body diagrams
combine forces at each joint into
a single “net force and moment of
force”
• measure external forces and their
points of application
• compute net forces and moments
starting at distal segment then
proceeding up the chain
Mankle k
Biomechanics Lab., University of Ottawa
Fankle
Fground
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External Work
• Inverse Dynamics Method
– compute net moments of
force at each joint
• Integrate (sum) over time
and sum over the powers
produced by the net
moments of force at each
joint (j)
• External work =
S (S Mj wj Dt) = S (SPj Dt)
Biomechanics Lab., University of Ottawa
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Internal Work by the
Absolute Power Method
• take absolute values of
moment powers
• sum over all joint moments
and over duration of
movement
• Total mechanical work =
S (S | Mj wj | Dt) = S (S | Pj | Dt)
• Internal work = Total mechanical work – External work
Biomechanics Lab., University of Ottawa
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Moment Power Analysis
• compute the angular velocity of the
joint
• compute the net moment of
force at the joint
20.
Extending
0.
-20.
Flexing
SR11BJ
300. Extensor
• multiply angular velocity and
moment of force to obtain the
“moment power”
0.
-300.
Flexor
2000. Concentric
• this is the power produced by the
net moment of force acting across the
joint
• it is mainly caused by muscle forces
0.
-2000.
Eccentric
CFS
CTO
-4000.ITO
0.0
0.1
0.2
Time (s)
Biomechanics Lab., University of Ottawa
IFS
0.3
0.4
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Moment Power Analysis
• angular velocity determines
whether joint is flexing or
extending
• net moment of force
indicates which “muscle
group” or “single equivalent
muscle” is acting
20.
0.
-20.
• positive power shows
“concentric work” while negative
power shows “eccentric work”
Flexing
SR11BJ
300. Extensor
0.
-300.
• moment power tells what the
moment of force is doing
Extending
Flexor
2000. Concentric
0.
-2000.
Eccentric
CFS
CTO
-4000.ITO
0.0
0.1
0.2
Time (s)
Biomechanics Lab., University of Ottawa
IFS
0.3
0.4
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Limitations & Errors
• can only be used on “free-ended”
extremities or extremities where
external forces can be measured (by
force platforms or force transducers)
• cannot be used with closed kinematic
chains (slap shot, golf, batting, etc.)
• assumes elastic storage and release of
energy is due to muscle eccentric and
concentric work, respectively
• assumes no multijoint
transfers of energy
• therefore overestimates internal work
Biomechanics Lab., University of Ottawa
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External, Total and Internal Work
Absolute work method
Absolute power method
Wexternal = Sn (D Etotal body )
= Efinal − Einitial
W*external = Sn (S Mj wj Dt)
= Sn (SPj Dt)
Wtotal = Sn | D Etotal body |
W*total = Sn (Sj | Mj wj | Dt )
= Sn (Sj | Pj | Dt )
Winternal = Wtotal − Wexternal
W*internal = W*total − W*external
Biomechanics Lab., University of Ottawa
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