Supplement to '' Nature, ''July 14, 1923 



litres per minute : if for five minutes, 34-2 litres 

 altogether, or 6-8 litres per minute. The reason why he 

 can run faster in a short race than in a long one is that 

 his average rate of expenditure of oxygen can be higher. 

 Now the following table gives the best performances, 

 at various fiat distances, of this subject, together with 

 calculations therefrom, on the above assumptions : 



Time .... 



Average speed, 

 metres per min. 



Oxygen avail- 

 able in this time 

 (lit.) .... 



Oxygen require- 

 ment per min. 

 at this speed 

 (lit.) .... 



If, therefore, the maximum rate at which a fit man 

 can run a given distance does depend only upon the 

 amount of oxygen he can obtain (a) out of income 



S?E6-3 ne^^es rei! r) wore. 



300 373 5:53 ifo 



Fig. 4. — Oxygen requirement per minute for running at different speeds : 

 calculated from the data in the previous Table. 



through the lungs and circulation, and {b) on credit, 

 then, knowing the maximum intake and the maximum 

 credit, one can calculate the requirement at the different 

 speeds. Running at 306 metres per minute, apparently 

 about 5*5 litres of oxygen per minute were required ; 

 at high speeds much more ; at the highest speeds enor- 

 mously more (Fig. 4). 



It is instructive therefore to inquire, by direct 

 experiment, whether the oxygen requirement of running 

 really has the value we have calculated, whether it 

 really rises so rapidly as the speed of running is in- 

 creased. The oxygen can be measured as before. It 

 is necessary to take into account not only the oxygen 

 actually taken in, but also the increase in the oxygen 

 debt during the period of running. The subject stands 

 at rest and measures his resting oxygen consumption ; 

 he runs 100 yards at the required speed ; during the 

 run and in the following fifteen minutes his oxygen 

 intake is measured ; from this is subtracted the oxygen 



he would have used had he remained at rest the whole 

 time ; the remainder is the oxygen consumption due 

 to the exercise, during and in complete recovery from 

 it. The result is exactly as shown in the figure : the 

 measured oxygen requirement rises continuously as the 

 speed is increased, attaining enormous values at the 

 highest speeds. Hence we may conclude that the 

 maximum time for which an effort of given severity 

 can be maintained is determined mainly by considera- 

 tions of the oxygen supply, actual or potential, to the 

 active muscles. 



Economy of Movement. — This leads us to the 

 important practical question of what is called the 

 " efficiency " of movement. Clearly if a given move- 

 ment can be carried out more economically, i.e. at the 

 expense of less energy, then less oxygen will be required 

 for it, and its maximum duration can be increased. 

 It seems probable that the difference between a good 

 long-distance runner and a bad one may often be due, 

 not to the fact that the good runner has a more effective 

 mechanism for supplying his muscles with oxygen, but 

 rather to the fact that he carries out his movements 

 with greater economy. In any category of muscular 

 effort the unpractised person will use inappropriate 

 muscles and movements, or will use the appropriate 

 muscles with an inappropriate force or rhythm. Some 

 people's nervous systems are naturally athletic : the 

 pictures they form of muscular movement, in terms 

 of the sensations which it gives them, are clear, vivid, 

 and sharp : they realise easily, from its subjective 

 aspects, the most economical, the most effective, and 

 the most convenient manner in which to employ and 

 co-ordinate their various muscles, both in the power, 

 the phase, and the rhythm of their several re- 

 sponses. Other people are clumsy, ineffective, and 

 uneconomical. 



If the timing of the valves of a motor, or the timing 

 of the spark, be wrong, or if the valve clearance be not 

 correct, the efficiency drops ; so it is in an animal : 

 if the muscles do not react with one another in the 

 right phase, with exactly the requisite force, and in 

 the appropriate rhythm, the movement becomes un- 

 economical. This economy of effort can, in part, be 

 taught : but just as all the practice in the world will 

 not turn some quite intelligent people into mathe- 

 maticians, so all the practice in the world may never 

 turn some quite powerful and well-developed people 

 into first-class athletes. Training and practice are 

 essential, but they can only build on an aptitude 

 already there. If a subject use his muscles uneconomic- 

 ally, if — so to speak — the timing and clearance of his 

 valves be wrong, he will need an excessive supply of 

 oxygen. Consequently he will be an ineffective athlete, 

 or an ineffective workman : he is uneconomical. Athletic 



