MECHANICAL WORK, ENERGY, AND POWER - Biomechanics and Motor Control of Human Movement - page 139

MECHANICAL WORK, ENERGY,
AND POWER

6.0 INTRODUCTION

If we were to choose which biomechanical variable contains the most infor-
mation, we would be forced to look at a variable that relates to the energetics.
Without that knowledge, we would know nothing about the energy flows that
cause the movement we are observing; and no movement would take place
without those flows. Diagnostically, we have found joint mechanical pow-
ers to be the most discriminating in all our assessment of pathological gait.
Without them, we could have made erroneous or incomplete assessments
that would not have been detected by EMG or moment-of-force analyses
alone. Also, valid mechanical work calculations are essential to any efficiency
assessments that are made in sports and work-related tasks.
Before proceeding, the student should have clearly in mind certain terms
and laws relating to mechanical energy, work, and power, and these will now
be reviewed.

6.0.1 Mechanical Energy and Work
Mechanical energy and work have the same units (joules) but have different
meanings. Mechanical energy is a measure of the state of a body at an instant
in time as to its ability to do work. For example, a body which has 200 J of
kinetic energy and 150 J of potential energy is capable of doing 350 J of work
(on another body). Work, on the other hand, is the measure of energy flow
from one body to another, and time must elapse for that work to be done. If