the mechanics of muscle action 287 



The iMechanics of Muscle Action. 



In a steam engine the energy liberated by combustion 

 is in the form of heat. Only part of this energy can be 

 converted into motion and into the lifting of weights or 

 overcoming of resistance of various kinds. The rest of 

 the energy is lost as heat. In the best steam engines the 

 amount of heat energy that can be converted into work 

 represents only ten to fifteen per cent of the entire energy 

 liberated by the combustion. We express this relation 

 of the useful energy to the total energy liberated in any 

 given machine, as the efficiency of the machine. A steam 

 engine, then, has an efficiency of only 10% to 15%. Ex- 

 periments with the muscles have demonstrated that the 

 ordinary muscle has an efficiency of something like 33%. 

 In other words, nearly a third of the energy liberated in 

 the combustion of fuel in the muscle cell can be converted 

 into useful work, while the rest is lost in heat. While, 

 perhaps, this amount seems small compared with the 

 heat loss, if we compare the muscle with the best steam 

 engines it will be seen that it is a remarkably efficient 

 machine. This efficiency represents an average, and dif- 

 fers in individuals. 



The simplest method of expressing this useful energy in 

 any machine is in terms of the weights or resistance which 

 is overcome and the distance through which the action 

 takes place. Thus, the energy necessary to raise a pound 

 one foot is expressed as one foot pound of energy. In other 

 words, work is equal to the force exerted, times the distance 

 through which it acts. In formula: Work = Force 

 X Distance. It is evident from this formula that a given 

 amount of energy may move a large body a short distance 



