THE PHYSIOLOGY OF MUSCULAR WORK 235 



and to the hindrances offered to the free passage of the blood 

 through the heart. For these reasons it is necessary to consider 

 the nature of the muscular exertion in any discussion of its effects 

 upon the blood pressure. 



M'Curdy ( 27 ) has drawn special attention to this question ; 

 he recorded the blood pressure in seventy-seven experiments upon 

 twenty-three men before, during, and two or three minutes after 

 an exercise of strength or effort. The exercise consisted in the 

 maximum lift for each man ; the weight lifted varied from 118 to 

 249 kilos., and the time of an average lift was five seconds. The 

 following are the average values of all the measurements : 



Blood Pressure in Mm. Hy. 



The highest blood pressure before the lift was 127 mm. Hg., 

 the lowest 93 ; the maximum during the lift was 210 and the 

 minimum 146. The rise in blood pressure was not accompanied 

 by any great change in the pulse rate ; some men showed an in- 

 crease, others no change, and others a decrease. Such exercises 

 subject the heart and blood vessels to a great and sudden strain, 

 and cannot be considered beneficial. A man must be carefully 

 and progressively trained to lift great weights ; otherwise there is 

 a great danger of overstrain of the heart. 



These results may be compared with those obtained by 

 Bowen (^J, who investigated the changes in the beat of the heart 

 and the blood pressure during bicycling. He found that there 

 was a rapid rise in the blood pressure when the work began ; the 

 maximum was reached in about four minutes, but during the con- 

 tinuation of the exercise the pressure declined slowly. The extent 

 of this fall depends upon the dilatation of the blood vessels of the 

 skin, and this in turn depends upon the temperature of the body 

 and its surroundings. This factor does not come into play during 

 an effort such as a lift ; the powerful and sustained contraction 

 of the muscles during the lifting of a weight nearly obliterates the 

 lumen of the blood vessels, and thereby increases the peripheral 



