Muscle power at joint is product of net muscle moment and angular velocity

Work done by a muscle

Differential work

Work along a path

Special case: F and v are collinear

Reaction forces and velocities at a joint.Mechanical power (rate of mechanical energy transfer) equals dot product of force and velocity.

Eta+, eta- are efficiencies of positive and negative work

Flow of energy from metabolic to external mechanical work

Total energy in a muiltisegment system

Center of mass approach

Energy for movement is reflected in the kinetic and potential energy associated with translation of the body cnetr of mass. Cavanaugh et al 1966 & many more.

CoM is a vector sum of masses and accelerations, so ppositely directed accelerations cancel. B ut energy is a scalar. CoM approach neglects energy associated with causing limb movements in opposite directions.

Therefore this approach grossly underestimates mechanical energy of body movement.

Sum of segment energies approach

Fixes some of the shortcomings of the CoM approach. Still underestimates work done since it fails to capture positive and negative work done at multiple joints.

Joint power and work

Improvement on the sum of segment energies approach. Identifies positive and negative work done at each joint. Still underestimates work associated with muscle co-contraction.