Changing Objectives of Optimization

유리

Movement Research Lab

Topics1. Metabolic energy expenditure minimization(new)2. Co-activation parametrization

Topics1. Metabolic energy expenditure minimization(new)2. Co-activation parametrization

Metabolic energy expenditure(old) = Metabolic energy expenditure

= + + +

= muscle activation heat rate = muscle maintenance heat rate = muscle shortening heat rate = positive mechanical work rate

W ANG , J. M., H AMNER , S. R., D ELP , S. L., AND K OLTUN ,V. 2012. Optimizing locomotion controllers using biologically-based actuators and objectives. ACM Trans. Graph. (SIGGRAPH2012) 31, 4.

Coactivation foranterior tibialis / lateral gastrocnemius(old)Muscle actuation Joint torque Metabolic energy

Anterior TibialisLateral Gastrocnemius

Metabolic energy expenditure(new)E = Metabolic energy expenditure

E = mi · ai

mi = mass of i-th muscle ai = activation of i-th muscle

Coactivation foranterior tibialis / lateral gastrocnemius(old)Muscle actuation Joint torque Metabolic energy

Anterior TibialisLateral Gastrocnemius

Coactivation foranterior tibialis / lateral gastrocnemius(new)Muscle actuation Joint torque Metabolic energy

Anterior TibialisLateral Gastrocnemius

Energy consumption & Coactivation

Muscle actuation < Metabolic energy < Joint torque

150cal/m < 170/m < 180cal/m

Topics1. Metabolic energy expenditure minimization(new)2. Co-activation parametrization

Co-activation parametrization

0 0.1 0.2 0.3 … 0.9 1.0

Joint torqueMuscle activation

Co-activation parametrizationRange of muscle activation

0 ≤ a ≤ 1

When a = 0, muscle is fully relaxed exerting no active force

When a = 1, muscle is exerting its maximum force

0.1

0.2

…

Co-activation pair?How can we define muscle co-activation pairs?

Ex)anterior tibialis & lateral gastrocnemius

THANK YOU FOR YOUR ATTENTION.