234 THE PHYSIOLOGY OF MUSCULAR WORK 



straps of the equipment as well as the load produce a hindrance 

 to free breathing, but nevertheless the engorgement of the liver 

 must be considered as a means of relieving the heart from still 

 greater distension. The tendency to strain upon the heart is 

 diminished by its increased beat, for the area of the inner surface 

 of the ventricle exposed to the pressure of the blood is diminished 

 during its contraction. 



After severe exercise the pulse shows an exaggerated dicrotic 

 notch ; this has been observed in a considerable number of healthy 

 men, and is no doubt a normal sign of the reaction to the high 

 blood pressure during work. The following figure is a repro- 

 duction of a tracing obtained from the radial artery of an athlete 

 on the day following a severely contested game of Rugby football 

 in a " cup-tie " match. 



The blood pressure is the force exerted by the blood upon the 



The rate of the pulse was 72 per minute. 



walls of the blood vessels, and is dependent upon the pumping 

 action of the heart and the resistance of the vessels, especially of 

 the arterioles. The blood pressure will be raised by a more rapid 

 or more powerful contraction of the heart, if the peripheral re- 

 sistance remains the same or does not diminish in proportion to 

 the increase in the work done by the heart. During muscular 

 work it is known that the peripheral resistance varies ; the vessels 

 supplying the muscles are dilated, and, if the exercise is continued 

 and the temperature 'of the body rises, the cutaneous arterioles 

 expand. This statement applies to those forms of exercise or 

 work in which there is no prolonged straining effort ; directly the 

 muscles of a limb are rigidly contracted and the thorax is fixed 

 in order that a better purchase may be given to the contracting 

 muscles, as, for example, in lifting a heavy weight, or in wrestling, 

 a great peripheral resistance may be introduced. During some 

 efforts the pulse may disappear at the wrist owing to the com- 

 pression of the arteries by the forcible contraction of the muscles 



