88 



NA TURE 



[November 23, 1899 



to repair brain waste, and which we hereafter call "Brain 

 Waste " ; second, that required to supply the nerve action, 

 which energises the muscles when ordered to do so by the 

 brain, and which we hereafter call "Nerve Waste " ; and third, 

 that for the upkeep of the muscles themselves, and which we 

 hereafter call " Muscular Waste." Hitherto writers have, we 

 believe, given too much prominence to the last-named of these. 

 We think that, instead of being the most important of all and 

 taking the largest share of food, it is probably the least im- 

 portant of the three. Dr. E. Turner has shown a method of 

 estimating, with considerable scientific accuracy, the proportions 

 of the food supply required by the above three sources of waste. 

 He has noticed that the proportions of uric and phosphoric 

 acids present in the human urine after exertion give the measure 

 of the brain and nerve wastes relatively to the urea present, 

 which is a measure of the muscle waste. A long series of ex- 

 periments have made us feel reasonably certain that the nerve 

 waste is practically proportional to the number of times that 

 the nerve centres energise the muscle in order that it 

 may make a stroke ; in other words that the nerve 

 waste is proportional to the number of revolutions of 

 the crank shaft of the cycle, and it is doubtless this fact that 

 has led to the craving for high gearsf which allow of a reduced 

 number of crank revolutions, as riders have found that by 



pedal during the entire revolution of the crank shaft in order to 

 drive his cycle at the required speed. We measure the total 

 resistance or pull of the cycle on the road in lbs. , and call it 

 total resistance expressed by our symbol " R," the power 

 exerted by the cyclist, that is, the rate of doing work in foot 

 pounds per minute by the symbol " P," and the work done in 

 foot pounds per hour by the symbol "W." So long as the 

 crank lengths are kept constant, or nearly so, the term geared 

 to 60 or 70, as the case may be, give a sufficiently accurate idea 

 of how far the pedal pressure " F" is influenced by the ratio of 

 revolutions of the crank shaft to that of the driving wheel, but 

 immediately the crank length is varied this term gear leads to 

 confusion. We think a better term is multiple, which we 

 denote by the symbol " M." " M " is the figure by which the 

 angular speed of the feet or pedal is to be multiplied in order to 

 get the lineal speed of the cycle moving along the road, con- 

 sequently R multiplied by M gives F. We have prepared 

 several tables which give the value of " R" for speeds varying 

 from 5 to 20 miles an hour. It will be seen that " R" consists 

 of three parts, ri, r2, and r^. r\ is the mechanical friction ot 

 the cycle, r2 is the road rolling and tyre resistance ; these two 

 first are functions of the weight of the machine and its 

 rider, ^3, the most important of all, is that due 

 to air resistance. In a second table we have the 



Table I. — Giving Values of R for a Rider and Cycle weighing 190 lbs. at Speeds from 5 to 20 miles an hour. 



reducing the number of crank revolutions they can economise 

 their nerve waste so as to leave a greater reserve of food energy 

 to supply brain and muscular waste. Our attention was directed 

 to this at a very early stage in our experiments ; but we found 

 that a limit was soon reached to the raising of the gear, as if 

 the crank length is kept constant the crank pressure necessary 

 to drive the cycle increases just as the gear is increased, so that 

 a strain is brought on the muscles at times of facing high winds 

 or climbing steep hills, which is greater than the muscles can 

 stand without muscular soreness setting in ; in fact, the limit 

 of strain is surpassed, which it will be convenient to call the 

 "elastic limit" of the muscles, and whenever this "elastic 

 limit" is passed for more than a few minutes the muscle is 

 temporarily weakened for the remainder of the day's run ; in 

 fact, the repair of that muscle cannot be made until the rider 

 rests and sleeps as well. 



We have adopted this term " Elastic Limit " of the muscles 

 because it corresponds very closely to a term well known to 

 mechanical engineers when used to express the extent to which 

 metals may be strained or stretched without taking permanent 

 set ; so long as they are subjected to strains within this limit no 

 permanent injury is done to the metal, whereas if it is passed 

 the structure of the metal is altered and becomes weaker and 

 liable to fracture. This process of being strained, even to a 

 small extent above the elastic limit, has "been sometimes called 

 the fatigue of metals, and is somewhat analogous to the fatigue 

 of muscles strained above their elastic limit. 



We use the term "Pedal Pressure" and symbol "F" to 

 e xpress the pressure in lbs. which the rider must apply at the 



value of F worked out for various multiples, and in 

 a third table we give the value of F under maximum con- 

 ditions of hill climbing at a speed of 8 miles an hour. From 



Table III. — Values of F in lbs. on Various Hills with 

 Different Values of M at% miles an hour. 



M = 4^ I 38-160 



M = 5 j 42-40 



M = 5| I 46-640 



M = 6 I 50-88 



43-875 

 4875 

 53-625 

 58-50 



52425 

 58-25 

 64075 

 69-90 



66-645 

 74-05 

 81-455 

 88-86 



95-175 

 105-75 

 116-325 

 126-90 



these tables we are able to show that we have to deal with 

 values of F varying from 18 lbs. to 130 lbs. It will be seen that 

 the F required by an average rider using a multiple of 5 when 

 he is maintaining a speed of 12 miles an hour on a calm day will 

 vary between 18 lbs. and a maximum of 106 lbs. when he is 

 climbing hills of i in 10 at a reduced speed of 8 miles an hour. 

 These figures are representative as average conditions of the 

 forces which have to be exerted by riders, although it is need- 

 less to say that far greater values of Y are reached by riders 

 when racing or in hill-climbing competitions. 



We have endeavoured to give some approximate value of the 

 elastic limit of muscles, and have made extended experiments to 

 settle this point. In the case of one of the writers, the elastic 



NO. 1569, VOL. 61] 



