160 SECTIONAL ADDRESSES. 
It is possible for a man to make an effort far in excess of any contem- 
porary supply of oxygen. This effort will require oxygen afterwards, 
and the total oxygen needed per minute to maintain the exercise can be 
measured. It is what we call the ‘ oxygen requirement’ characteristic 
of the effort involved. Now experiments have shown (see fig. 2) that the 
PER MINUTE 
LITRES 
SPEED 40 80 120 160 200 240 280 320 
Fic. 2.—Observations of oxygen requirement of K.F. running and standing- 
running at various speeds. Horizontally, speed : running, metres per minute ; stand- 
ing-running, steps per minute. Vertically, oxygen requirement per minute, litres. 
oxygen requirement varies very largely with the speed: it increases far 
more rapidly than the speed, more like the second or third power of the 
speed, so that high speeds and intense efforts are very wasteful. These 
facts enable us approximately to deduce the general form of fig. 1. 
Imagine an athlete with a maximum oxygen intake of 4 litres per 
minute,’ capable of running until his maximum oxygen debt has been 
incurred of 15 litres. If he runs for 15 minutes the total oxygen avail- 
able during the exercise and in arrears is 15 *4-++15=75 litres : an effort can 
be made requiring 5 litres of oxygen per minute. Imagine, however, that 
he exhausts himself not in 15 but in 5 minutes : the total oxygen available 
during or in arrears is 5X 4+15=35 litres. He may exert himself more 
violently, therefore, with an effort equivalent now to 7 litres per minute. 
Tmagine next that he runs himself to exhaustion in 2 minutes: 42-15, 
z.e. 23 litres of oxygen are available, 11°5 per minute; a correspondingly 
greater effort can be made. By such calculations it is possible from fig. 1 to 
deduce a relation between oxygen requirement and speed. Taking the case 
of a man swimming, the result is shown in fig. 3 on the assumption of 
1 Assumed, for the sake of simplicity in calculation, to commence as soon as the 
race begins. For a more accurate calculation the gradual rise of the oxygen intake 
at the beginning of exercise can be taken into account. 
Ne 
