EFFECT OF EXERCISE ON CIRCULATION 1101 



the case of a trained individual, as is seen in the Table quoted 

 above. 



SECOND WIND. It is a familiar experience that in a running 

 race of any duration the competitors after some time become less 

 distressed than at the commencement of the race. The runner is 

 now said to have got his ' second wind,' and can continue running 

 with apparent comfort. There are several factors which may account 

 for this accommodation. In the first place, as a result of the produc- 

 tion of metabolites in the contracting muscles, their vessels may be 



FIG. 456. Curve showing the effect of a sudden rise in the arterial resistance on 

 the output and volume of the ventricles. Systole causes a downward move- 

 ment of the lever. 



H heart volume ; BP, arterial blood pressure ; s, signal showing duration 

 of stimulation of splanchnic nerve ; T, time-marker, 10 sees. 



more dilated, so that the flow of blood through them is easier. M.ore 

 important is the change in the heart accompanying the onset of 

 second wind. As Pembrey and Cook have shown, the onset of second 

 wind is always attended with a diminution in the pulse-rate. At the 

 same time there is an alteration in the respiratory quotient. During 

 distress the respiratory quotient is high, i.e. more carbon dioxide is 

 being given out than oxygen taken in. As the distress diminishes, 

 the respiratory quotient also falls. The improved action of the heart 

 may be partly due to the increased coronary circulation, since a 



