170 



SECTIONAL ADDRESSES. 



of the human agent instead of as a driver of these capacities, it counts 

 as a gain. Just so soon as the function of speed is dissociated from 

 its effects on the worker we revert to the old system of pace-making 

 and speeding. ' 



These are the observations of field workers. Can they be substan- 

 tiated by experimental work in the laboratory? Benedict and I found, 

 for example, working with a carefully calibrated bicycle ergometer, tliat 

 there was a very close connection between the speed at which work 

 was done and the mechanical efficiency. There was a very definite 

 falling off with increased speed, as the following table shows. Unfortu- 

 nately it was impossible to get our subject to pedal slower than 70 revo- 

 lutions per minute. 



We found further that if the amount of effective muscular work 

 done was kept constant, the efficiency fell with an increase of 

 speed. Thus with effective work equivalent to 1.95 calories performed 

 at the rate of 90 and 124 revolutions per minute respectively with the 

 lower speed, the net efficiency was 22.6 per cent., whereas with the 

 higher speed it fell to 15.7 per cent. Or again, with effective work 

 of 1.58 calories at 71 and 108 revolutions per minute the efficiency was 

 24.5 per cent, and 15.6 per cent, respectively; and finally, with effective 

 work of 1.35 calories at speeds of 71, 94, and 105, the efficiencies were 

 23.1, 20.4, and 17.0 per cent. 



A. V. Hill has also' recently dealt with this problem in a most 

 interesting piece of work, where the activity was strictly confined to 

 the biceps and the brachialis anticus. He demonstrated very clearly 

 that, in spite of the fact that the slower the contraction the greater was 

 the amount of work done, all the advantage thus gained was rapidly 

 neutralised and dissipated as the result of the slow contraction neces- 

 sarily causing an increased degradation of energy in the way of physio- 

 logical changes resulting from the maintenance of contraction. It thus 

 followed that a slow contraction, powerful though it might be, was 

 not necessarily one of high efficiency. The actual efficiency, i.e. the 

 ratio of the external work done to the energy degraded in carrying it 

 out, was found to pass through a definite maximum value as the duration 

 of the contraction increased. The maximum efficiency in his series of 

 experiments was 26 per cent. He found that it was very rapidly 

 attained, the optimum for the muscles investigated being apparently just 

 under one second, but the fall which followed, as the duration of the 

 contraction increased, was a comparatively slow one. On account, 

 therefore, of the blunt nature of the curve the efficiency remained more 

 or less constant over a wide range of speeds. 



