Moment Power Analysis and Absolute Power Method D. Gordon E. Robertson, PhD, FCSB Biomechanics Laboratory, School of Human Kinetics, University of Ottawa, Ottawa, Canada 1Biomechanics Lab., University of Ottawa

2 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

Biomechanics Lab., University of Ottawa3 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 =  j  j  t) =  P j  t)

Biomechanics Lab., University of Ottawa4 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 =  j  j  t) =  P j  t) Internal work = Total mechanical work – External work

Biomechanics Lab., University of Ottawa5 Moment Power Analysis compute the net moment of force at the joint multiply angular velocity and moment of force to obtain the “moment power” this is the power produced by the net moment of force acting across the joint it is mainly caused by muscle forces compute the angular velocity of the joint

Biomechanics Lab., University of Ottawa6 Moment Power Analysis net moment of force indicates which “muscle group” or “single equivalent muscle” is acting moment power tells what the moment of force is doing positive power shows “concentric work” while negative power shows “eccentric work” angular velocity determines whether joint is flexing or extending

Biomechanics Lab., University of Ottawa7 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

External, Total and Internal Work Absolute work method W external =  n  E total body ) = E final − E initial W total =  n  |  E total body | W internal = W total − W external Absolute power method W* external =  n  j  j  t) =  n  P j  t) W* total =  n  j  j  j  t ) =  n  j  P j  t ) W* internal = W* total − W* external Biomechanics Lab., University of Ottawa8