68 PHYSICAL ASPECTS OF MUSCLES 



Fig. 30. An experiment to show that with a given energy you can either 

 slowly exert a large force through a small distance or rapidly exert a small force 

 through a large distance. This is demonstrated by having your partner offer 

 either a large or small resistance to your push. 



is corrected to 



(P + a/V 2 )V = constant, 



where the term with a is included to account for the work the gas mole- 

 cules do to pull apart from each other in the process of expanding to 

 exert a pressure P throughout the surface of the volume V of the con- 

 tainer. 



There is a second correction to the perfect gas law which takes account 

 of the finite volume of the molecules by subtracting this volume, called 

 6, from the total volume, since the container cannot be made smaller 

 than the volume occupied by the molecules. In the case of muscle, there 

 is a similar correction for the contraction rate of the muscle itself. Thus 

 Hill's characteristic equation for muscle action, 



(P + a)(V + b) = constant, 



can, by suitable choice of the two arbitrary parameters, be made to fit an 

 extremely wide range of data on muscle contraction. The constant value 

 can be readily determined, since when maximum force is being exerted 

 the muscle will have its smallest contraction rate, which is b. Thus the 

 constant is simply P max b. 



If the statement above seems implausible to you, you may familiarize 

 yourself with the point by a simple experiment. Have a friend hold his 

 hand facing you with palm vertical, as in Fig. 30. Now ask him to do 

 the following when you push on his hand. First, have him offer little 



