MECHANICAL WORK, ENERGY, AND POWER - Biomechanics and Motor Control of Human Movement - page 141

that to the rate of change of energy of the segment. Thus if, t is 20 ms,
E s /t 300 W.

Another aspect of energy conservation takes place within each segment.
Energy storage within each segment takes the form of potential and kinetic
energy (translational and rotational). Thus, the segment energy E s at any given
point in time could be made up of any combination of potential and kinetic
energies, quite independent of the energy flows into or out of the segment. In
Section 6.3.1, the analysis of these components and the determination of the
amount of conservation that occurs within a segment over any given period
of time are demonstrated.

= 200 + 120 + 265 − 85 − 10 − 190 =

6.0.3 Internal versus External Work
The only source of mechanical energy generation in the human body is the
muscles, and the major site of energy absorption is also the muscles. A very
small fraction of energy is dissipated into heat as a result of joint friction and
viscosity in the connective tissue. Thus, mechanical energy is continuously
flowing into and out of muscles and from segment to segment. To reach an
external load, there may be many energy changes in the intervening segments
between the source and the external load. In a lifting task (see Figure 6.2), the

Figure 6.2 Lifting task showing the power generation from a number of muscles and
the combined rate of change of energy of the body (internal work) and rate of energy
flow to the load (external work).