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Moment Power Analysis and Absolute Power Method. D. Gordon E. Robertson, PhD, FCSB Biomechanics Laboratory, School of Human Kinetics, University of Ottawa, Ottawa, Canada. Inverse Dynamics Review. divide body into kinematic chains divide chains into segments
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Moment Power Analysis andAbsolute Power Method D. Gordon E. Robertson, PhD, FCSB Biomechanics Laboratory, School of Human Kinetics, University of Ottawa, Ottawa, Canada Biomechanics Lab., University of Ottawa
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 Ottawa
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
Internal Work by theAbsolute 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
20. Extending 0. -20. • compute the angular velocity of the joint SR11BJ Flexing Extensor 300. • compute the net moment of force at the joint 0. Power (W) Moment (N.m) Angular vel. (/s) -300. • multiply angular velocity and moment of force to obtain the “moment power” Flexor Concentric 2000. 0. -2000. Eccentric ITO CFS CTO IFS -4000. 0.0 0.1 0.2 0.3 0.4 Time (s) Moment Power Analysis • this is the power produced by the net moment of force acting across the joint • it is mainly caused by muscle forces Biomechanics Lab., University of Ottawa
20. Extending 0. -20. • angular velocity determines whether joint is flexing or extending SR11BJ Flexing Extensor 300. • net moment of force indicates which “muscle group” or “single equivalent muscle” is acting 0. Power (W) Moment (N.m) Angular vel. (/s) -300. Flexor Concentric 2000. • moment power tells what the moment of force is doing • positive power shows “concentric work” while negative power shows “eccentric work” 0. -2000. Eccentric ITO CFS CTO IFS -4000. 0.0 0.1 0.2 0.3 0.4 Time (s) Moment Power Analysis Biomechanics Lab., University of Ottawa
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
External, Total and Internal Work Absolute work method Absolute power method W*external= Sn (S MjwjDt) = Sn (SPjDt) W*total= Sn (Sj|Mjwj|Dt) =Sn (Sj|Pj|Dt) W*internal = W*total − W*external Wexternal = Sn (D Etotal body ) = Efinal − Einitial Wtotal = Sn| D Etotal body| Winternal = Wtotal − Wexternal Biomechanics Lab., University of Ottawa
