312 On the Energy expended in Propelling a Bicycle. 
power,* while the average furnished by all the experiments on nearly level ground 
—which we believe to be close to the average in ordinary road riding—amounts 
to between a seventh and a sixth of a horse-power. ‘This is very sensibly more 
than the work which the muscles of a man seem capable of effecting in other 
applications of them. Thus in rowing, or in raising one’s own weight, which are 
supposed to be two of the best ways of employing the muscles, the power which 
a man can exert for any continuance does not seem to reach much beyond the eighth 
of a horse-power. This in part accounts for the extraordinary feats which are daily 
being performed on bicycles, but it does not appear to give the whole account of the 
matter, for which we must look to physiology and psychology as well as to mechanics. 
In fact the real comparison to be made is not so much a comparison of the feats 
accomplished with the energy expended as with the fatigue incurred. And this in 
riding a bicycle is small, not only from the mechanical efficiency which the foregoing 
experiments show the machine to possess but also for other reasons. Part of these 
are physiological. The rider is seated on the machine, and thus relieved from what is 
the chief source of fatigue in walking, the weight of his own body on his l:mbs. 
He is in the posture best adapted to the healthy play of the vital organs in the 
chest, and the constant sieht movement of the muscles of the trunk contributes to 
this healthy play. Again, while the arms perform some of the work,+ the principal 
part is relegated to the most powerful muscles of the body, those of the leg. It is 
also material to observe that these limbs are left very unusually free in their 
movements, and that the choice of what length of stroke he will employ, what- 
force he will exert, and at what speed he will move his limbs, are left to the rider, 
who ean adjust these details to be what best suit his own body. How much 
depends on these adaptations will be appreciated by any person who has ridden far 
with a saddle too low forhim. The tatigue then experienced is sometimes accounted 
for by the supposition that the greatest pressure 1s exerted when the leg is nearly 
straight, and that the rider loses this most valuable part of the stroke ; but all our 
experiments concur in showing that this is not the case (see Fig. 4, Pl. 40, and Fig. 8, 
Pl. 41) and that on the contrary, the greatest force is exerted almost exactly at 
the middle of the stroke. The reason seems rather to be that unless the knee is 
periodically straightened, the tendons, nerves, or blood-vessels which pass it are 
subjected without intermission to some restraint which incommodes them. 
But besides the mechanical and the physiological elements, there is a third— 
an emotional element. This is the exhilaration felt in riding the bicycle, which 
* This is the maximum attained in our experiments, which were limited by the range of the spring of 
the indicating apparatus; but in actual riding this maximum is often largely exceeded for a short time, 
as in spurting up a short stiff hill, and on other like occasions. 
+ The contribution made by the arms when pulling on the handles often seems to the rider out of pro- 
portion to the force they exert. Perhaps in such cases their chief office is to stiffen the trunk, and so 
give firm points of attachment to the upper ends of the great muscles of the legs. 
