sanitate urbanorum · desanitate urbanorum ronaldwilliams the cities of the plain have always had...

BRITISH MEDICAL JOURNAL 22-29 DECEMBER 1979

Contemporary Themes

De sanitate urbanorum

RONALD WILLIAMS

The cities of the plain have always had their own specificproblems of public and private health, and although in Londonwe are now no longer much at risk from the forms of pox andpestilence which tormented Europe in the Middle Ages we aresusceptible to other kinds of disorder. Increasingly, we aresuccumbing to diseases that can be traced back to our verysuccesses, either in manipulating our environment and ourfood supply, or in converting various kinds of leaf, root, grape,or grain into highly appealing end products which, for many,carry an addictive hook. A major breakthrough in the lasthundred years has been the development of mechanical trans-port, and yet in large cities we are in danger of becoming over-dependent on this too, and of regressing into a state of cardio-vascular torpor for which our physiology is not designed, and forwhich our diet is inappropriate.

It may be helpful, therefore, to consider one way in whichthis particular hazard of modern society may be avoided, andto discuss in some detail that most civilised phenomenon, aman (or girl) on a bicycle: the most efficient movers, so far as isknown, in the solar system.' Weight for weight, the cyclist usesless energy to cover a given distance than even the superblyconstructed salmon or dolphin, not to mention birds, the greatcats, the motor car, or any form of jet or rocket engine.1 Whetherhe is more economical in energy than orbiting extraterrestrialbodies is another matter, but whatever other qualities theseintriguing objects may have, self-steering is certainly not oneof them. Energy comparisons are difficult because one does notknow what started them off, but the space probe which theAmericans plan to send out to investigate Halley's comet whenit returns in 1986 may give some clues. Until then, and probablyfor long after, the cyclist remains supreme. How does he do it,where does he stand in the natural order, and what about hishealth ?

Movers and levers

The power needed by a caterpillar to propel itself against groundresistance has been calculated theoretically to be 250 times, weight forweight, that needed by a cyclist. At 1 mph it is, to be precise, 5 5horsepower per long ton (2240 lb),' which sounds an awful lot ofcaterpillar but is really only a neat scientific way of setting out deducedfacts. The figure for the snake is much the same. Between theserelatively inefficient crawlers and the cyclist comes the whole rangeof what one might call the intermediate movers, like the Lotus or theFerrari or, to put them in order of decreasing ground resistance,leaping rabbits, walking men, running horses, and pneumatic-tyredmotor cars.' The rolling resistance of the racing bicycle-againweight for weight-is one-third that of the car3 and one-tenth that ofthe walker (whose legs in some respects may be regarded as the

spokes of a rimless wheel), and is bettered only by the steel-wheelrailway wagon on roller bearings. But metal rails are smooth com-pared with roads, and on rough surfaces soft-rimmed wheels offerless resistance than hard-rimmed ones. The bicycle manufacturersknow this, and so did the ancient Egyptians. In the eighteenthdynasty in 1400 BC they were applying rawhide wrappings to theirchariot wheels to make the tyres resilient.3The cyclist conserves momentum and kinetic energy in a way that

no other land animal can equal. The running of a quadruped orbiped is essentially a series of consecutive jumps,2 and even thecheetah at 80 mph is not moving with absolutely uniform forwardspeed, for there is an inevitable check each time its paws touch theground and it begins to lift its body over them. It is also clear that thevertical component of its kinetic energy is for the most part lost witheach leap, although some may be stored as strain energy in musclesand tendons.4 The cyclist loses no forward kinetic energy becausehe is on rolling wheels, and no vertical kinetic energy because hiscentre of gravity remains steady and does not bounce up and down,as it does with each repeated stride of everything that walks or runs.His advantage over animals whose jumps start from standstill ispredictably far greater, for the whole of their kinetic energy is lostwith each landing. This is why a kangaroo or a grasshopper has toexert a relatively large force to keep moving forward, and why therunning of a racehorse is more economical in energy than the leapingof a frog.2The cyclist has an important advantage in one other equally

fundamental respect-by comparison with all other limbed landanimals and the birds, he has to use only a minute fraction of hispower output in supporting his body weight. The fishes, of course,have no weight problem and are more smoothly streamlined, butthey have to move in a much denser medium.

But how much muscular work is the cyclist doing, for this is oneof the factors on which the health of his arteries may depend? Tomove at 12 mph (19-3 km/h)-a speed which would keep him aboutlevel with the winner of an Olympic marathon-a cyclist on a light-weight touring machine has to exert only 0 1 hp (74 6 W),3 andat this power output an unathletic individual is probably using aboutone-quarter of his maximum breathing capacity. Yet the trainingeffect of cycling only four miles each way to work at this modestspeed has been estimated-on the basis of comparative caloricrequirements-to equal that from 10 minutes' wrestling, over half-an-hour's squash, 50 minutes' tennis (singles), an hour's skating, abrisk 21 mile walk, or 24 holes of golf.5 If the cyclist chooses to rideharder at, say, 17 mph (27-4 km/h) these equivalents are aboutdoubled, and at 21 mph (33-8 km/h) they are tripled, becausealthough his tyre-rolling resistance and machinery friction increasein almost linear proportion with speed,3 the wind resistance that hehas to overcome is proportional to the cube of his velocity. It canbe seen, therefore, that as a means of benefiting our arteries wrestlingis very effective-although cycling is more comfortable-and golf, atleast as played in the United States, comes far down the list andshould probably be reserved for the elderly infirm and those whohave a serious problem in filling their leisure time. It is only fair toadd that figures from Scotland suggest a higher caloric expenditureby golfers there,6 but that could, of course, be the weather.The running, walking, or cycling man, in common with the

crocodile, rhinoceros, antelope, osprey, and ant makes use of asystem of extended levers. Lever systems of this kind are intrinsicallyefficient.3 Not only are they more economical in energy than themore primitive systems of some other animals-particularly the

Sloane Street, London SWlX 9SWRONALD WILLIAMS, MB, MRCP, general practitioner

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crawling of the caterpillar and the snake, in which the whole body isthe lever7-but they may easily be adjusted to the resistance en-countered, as when a walker or runner alters his stride in response to agradient. The cyclist has, instead, the less flexible benefit of gears,but there is a quite different advantage of the lever system whichcould in the future become of great importance to him. Whereastravel by foot or hoof requires a several-fold increase in power asbetween hard pavement and soft mud, the resistance to movement of awheel over these two kinds of surface may differ not by several-fold butby several hundredfold.3 This is why the Romans needed to buildpaved roads for their horse-drawn vehicles, and theirs was the firstcivilisation to do this. It took less time then to travel overland fromthe Channel to Rome than it did 1000 years later when this roadsystem had vanished through lack of maintenance.' One can see thebeginnings of the same process in Chelsea. This is not to suggestfor one moment that our road surfaces will get much worse-andcertainly not while North Sea oil holds out-but the cyclist canview even this possibility with equanimity for he, at least, will beable to squelch through the occasional patches of clay on his lower-limb levers, carrying his machine with him. The motorist will haveno such option.But levers have hinges and hinges need oiling, and the cyclist

lubricates his in a remarkably subtle way. The friction of a synovialjoint is about 10 times less than that of a metal-to-metal bearinghydrodynamically lubricated by oil.8 In a bearing of this kind theeffective oil pressure depends on the relative geometry of the movingsurfaces rather than on a pump,4 but, when movement ceases, thispressure is of course no longer generated. Apart from ball or rollerbearings, the only engineering systems which can maintain lowercoefficients of friction than a synovial joint over a range of speedsfrom zero are hydrostatically pressurised ones. In these the lubricant(oil or air) is continually forced to the bearing by an external pumpat a rate sufficient to maintain a fluid film, in spite of the inevitableleakage at the edge of the loaded region.8The cyclist, happily, needs nothing as crude or bulky as this.

Unlike the engine of a car, his bearing surfaces are permeable, and ina way which ensures that the lubricating fluid changes its physicalproperties to advantage when the joint is under load. The twoprincipal components of the matrix of cartilage are proteoglycans andcollagen.9 The collagen consists of highly cross-linked fibrils intension, and immobilised within this network are the proteoglycans-hydrophilic colloids which form with water a gel of high osmoticpressure. The swelling pressure of this proteoglycan-water gel isopposed, and in health completely contained, by the elastic restraintof the collagen mesh.10 Normal cartilage cannot swell, therefore, andalthough when under load it may creep a little, it does not contract.It is permeable to water and to solutes of molecular weight under70 000. The hyaluronic acid of synovial fluid has a molecular weightof 1 000 000; it therefore remains on the cartilage surface, and, asthe gap between the bearing surfaces becomes smaller, water andsmall solutes are squeezed through the cartilage leaving the synovialfluid more concentrated in hyaluronic acid within the pressure zone.9This results in a water-hyaluronic acid gel which provides a film0 02-0 03 Vum in thickness separating the joint surfaces and lesseningwear. At the same time, water is expressed from the other parts of thecartilage not under pressure so that the overall consistency of thesynovial fluid remains constant. The ionic and hydraulic equilibria,which operate from moment to moment in working cartilage, are of acomplexity and elegance which no engineering system can evenbegin to approach, and it is no wonder that the cyclist overtakes sosmoothly.

Health and safety of cyclingBut we are vulnerable. A hospital friend of mine recently pointed

out the GP's case on the back of my bicycle to a surgical colleague andsaid "That's his first-aid kit." Not quite accurate, but the point istaken. Fortunately, in my first 19 000 miles I have not needed anyfirst aid, but in any discussion about cycling and health this is not anissue that can be evaded. Using one of the most civilised of all formsof transport is no defence against drunken or unthinking behaviourbehind a driving wheel.The accident rate for cyclists in 1975 was calculated as 7-3 deaths

and 113 serious injuries per 100 million kilometres travelled," which,on the face of it, was about 10 times that for car and taxi drivers. Onthe basis of these figures the Government Green Paper on transportpolicy"2 claimed that cycling was "ten times as dangerous as driving acar for every mile travelled"-the car being hardly a paragon of


safety itself when compared with bus travel-and the Green Paperwent on to imply that for this reason cycling could not be seen as aserious alternative to other forms of transport in towns, and did notdeserve a great deal of consideration on the part of local authorities.Even so, there are various reasons why this statement is only a

partial truth."3 In the first place, the calculation of cycling milage was,at best, very approximate and probably an underestimate, as thefigures were based on the Department of Transport's 200-pointtraffic census, and the census points were chosen to give a representa-tive sample of roads used by motor and not cycle traffic. Proportionatelyfew of these were roads with light traffic, and yet it is these roadswhich are likely to carry a higher proportion of cyclists. Nor did thecensus include estate roads, bridleways, footpaths, or cycle ways, onwhich an appreciable amount of cycling is done, although anyaccidents on such routes were included in the figures.'3

But the most glaring slant in the Green Paper's interpretation ofcyclist casualty rates was the failure to distinguish between adultsand children. Cycling accident statistics include casualties from allage groups, whereas those for car drivers inevitably refer to thoseaged 17 and over. Yet, in 1974, 51 60% of cyclists killed or seriouslyinjured in Britain were under 17. It is likely that well over half thetotal cycle milage is done by over-17s, so that the casualty rate foradult cyclists is almost certainly far less that the overall figuressuggest.

Unlike motorists, cyclists rarely injure other people, and surelyit is the health and safety of the whole travelling public which shouldbe considered when public policy towards transport is being formu-lated. In present road conditions cycling is arguably more dangerousfor the cyclist, but it is incomparably safer for everyone else, andwhen all road users, including pedestrians, are taken into account thefigures as between car and bicycle take on a different complexion.

It is difficult to escape the conclusion that the 1976 Green Paper'sattempt to discourage cycling was motivated less by a concern for theoverall and future good of the community than by a reluctance totackle the difficult problems of mixed traffic in towns. Happily, thereis now welcome and visible evidence in London and elsewhere thatofficial policy towards the bicycle is softening. In view of the immenseecological price that we pay for the millions of cars that clog our cities,this is not before time.

Pedal power

The marvellously space-saving and, indeed, transparent mechanismby which the cyclist avoids overheating is in distinct contrast to thecumbersome cooling system of the motor car. For the cyclist movingfreely in the open, evaporative heat transfer through the skin isabout double convective heat loss,3 and the heat removal capacity ofthe air around him is more than sufficient to deal with any heat thathe can produce. A racing cyclist doing a fast 25-mile (40 km) timetrial in under an hour at a speed of 27 mph (43 5 km/h) maintains apower output of about 0 5 hp (373 W)3 and remains reasonablycomfortable. If he attempts the same output on a stationary bicycleergometer in a laboratory, and therefore in still air, he can expect tohave to give up in 10 minutes, by which time he will be sweatingprofusely and beginning to lose control of his body temperature. Ifthis happens at submaximal effort to a man in superb training, whatchance has the hopeful gourmet pedalling away in his bathroom ofputting in much muscular work before he, too, blows up?The source of the heat, of course, is the biological power unit

itself, the contractile protein of muscle, whose use or disuse marksout the widening division in our species to which Passmore first drewattention some 15 years ago.'4 While working in the department ofphysiology at Edinburgh he foresaw two divergent subgroups-Homo sportivus and Homo sedentarius-as the logical successors inWestern societies to Homo laborans, an earlier primate capable oftremendous physical work and endurance and once common in theseislands, where he was horribly exploited in mines and mills. Hisnumbers have become much less here, and indeed some would saythat in England he is now virtually extinct, although I do not myselfbelieve this. He is, however, still found in large numbers in other lessmechanised parts of the globe, It has been'suggested that Homosportivus is likely to be both happier and healthier than Homosedentarius,"1 as well as being less prone to obesity, atherosclerosis,and other degenerative diseases, and some recent work supports thisview.'There is evident parallelism between these two subgroups and

those defined in my earlier paper-Homo se propellens and Homo(vehiculo) constrictus"l-and it may well be that they are conspecific.


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My son's Latin master says that Homo sportivus does not exist, butI know he does because some of my closest friends are in this group.We have to remember that, unlike the wasteful and polluting

internal combustion engine-whether compression ignition (diesel)or spark ignition (private car)-human muscle is a system designedto run at uniform temperature. It, too, is subject to the second lawof thermodynamics, but in an especially simple form'8; in biologicalsystems free of thermal gradie.nts it is impossible to convert heat intowork, although work may be converted into heat very easily, as byfriction and viscosity. Heat is also produced by oxidative metabolism,the rate of which can increase by over 20 times when resting musclebecomes active.'8 It is yet another example of the astonishing spatialeconomy of the human engine that the same circulation whichprovides the muscles with their fuel and their oxygen also serves tokeep them cool, for to prevent overheating during prolonged activityof muscle fibres an increased local blood flow is essential.19The immediate source of energy for muscular contraction is ATP,

and this can be replenished virtually instantaneously by the anaerobicbreakdown of phosphoryl creatine and muscle glycogen. Longer-termrestoration of ATP depends on oxidation processes using muscleglycogen, blood-borne glucose, and blood-borne fatty acids, and it isfor these processes that the type I fibres of voluntary muscle areparticularly equipped. They are used for sustained effort, and,because they contain a higher proportion of myoglobin and cytochromesystems, are dark brown in colour.'0 Marathon runners have apreponderance of this type of fibre." 22 For the most part type IIfibres replenish their ATP anaerobically, are large in the sprinter, andpale in colour. This is the white meat of the turkey or the ptarmigan,the fight-or-flight meat, the type of muscle fibre needed by the100-metre man, the farmyard fowl, or the game bird for short burstsof violent activity which must necessarily be fuelled anaerobicallybecause by the time the slower oxidation processes can come intoplay the race is over or the predator has struck. The pectoral musclesof birds like the pigeon that fly long distances consist, as one wouldexpect, mainly of red meat.Th? cyclist uses both types of fibre, and the sheer sophistication of

the propulsive mechanism at his disposal compared with that of themotor car almost beggars description. Ask a Rolls-Royce to movewithout oxygen and it just sits and looks at you. Mechanical enginescan only wear out with use. Biological ones adapt; within limits, theycan even repair themselves, and the more they are exercised thebetter their performance. Their fuel supply improves, their oxygentransport system becomes more efficient as maximum cardiac outputrises and the capillary network in the skeletal muscle becomes moredense,2 ' and peripheral oxidative enzyme activity also increases.'4Fibre size increases with training, and the muscles themselves becomemore powerful, for the force that a muscle can exert is proportional toits cross-sectional area.Although the improved training brought about by regular cycling

does rnot alter the energy expenditure required for a given speed, itdoes reduce the cardiac and respiratory changes necessary to achieveit.25 The resulting improvement in his reserves is of considerablebenefit to the cyclist, for it delays the onset of muscle fatigue. Butmuscle fatigue and weakness is a common symptom of a wide rangeof disorders of body and mind,2' and the physical weariness of the

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trapped urban motorist quite clearly has other causes. His leg musclesas they dwindle will probably show a relative type II atrophy,27and, interestingly, it is these fibres that are affected in the metabolicmyopathies associated with steroids, hypothyroidism or hyper-thyroidism and vitamin D deficiency.'6The Roll-Royce has no standby system if it exhausts its fuel

reserves, and to offer it a litre of the highest proof spirit from its owncocktail cabinet gets one absolutely nowhere. The cyclist's manage-ment of his energy supply is much more flexible. Not only can heprolong his exercise performance in several ways-by far the mostimportant being his adaptations to training-but for extreme statesof muscle exhaustion and glycogen depletion he has in reserve theenzyme myokinase to catalyse the regeneration of his ATP'8 in anemergency and keep him going for a short time longer-a nice, ifrarely needed, bonus from the highly evolved chemistry of hiseveryday equipment. It will come as no surprise that the "aerobic"fibres which sustain the long-distance runner and the cyclist can alsobe used less vigorously and even isometrically in other protracted,but less worthwhile, pursuits. They are, for example, the antigravitymuscles of the public speaker, and they support the golfer in hischaracteristic stance-upright, unwavering, and alert-as he surveysthe middle distance and wonders which part of the thicket he shouldenter to retrieve his ball.

But at least golfers-when they move-do so on their limbs, whichis more than can be said for the frustrated motorists nosing their waythrough the polluted air and congested streets of London. And herewe must address a brief word to the sociologists, who seem not tohave noticed the extent to which these units of mobile manpowerhave become habituated (within the general framework of the urbantransport situation) to visualising themselves (in an inner-city spark-ignition four-wheel-vehicle context) as being in occupancy of thefront driving seat in an ongoing management role. Indeed, they arenow physiologically so disadvantaged (by comparison with theirtwo-wheel-utilising non-petrol-dependent self-propelling counter-parts) that it is little short of scandalous that no parliamentary com-mittee has yet been set up to consider how they may be helped. Aninterdisciplinary pilot study (under a project steering team) is longoverdue to initiate the necessary research activity-firstly, to clarifyand quantify problems as they arise, and, secondly, to contribute tothe scientific work of description and conceptualisation in formulatingand defining within agreed parameters the areas of deprivation inrespect of the basic haemodynamic human needs of this increasinglyslow-moving societal group.

I shall start the ball rolling-and return with some relief to thelanguage of my fathers. The pathognomonic features are fairlyobvious: the impatient feet inert on the pedals, the forearms weakfrom months of power-steering, the thrusting ego stopped-orscarcely moving-the vacant stare, the hopeless fixed expression, theperiodic sighing respiration, the intermittent gnashing of the dentures.It is not a pretty list, but the inextricable web of pathology building upinside these imprisoned primates is even worse. Suffice it to say that inmany cases their high-density lipoproteins will be at abysmal levels,and their narrowing arteries almost awash with lipids. Indeed, theirtissues generally, and certainly their intellectual edge, will reflect to aworrying degree the deficiencies and uncertainties of their only life-line, the sluggish circulation of the too-much-sitting man.Nor should the psychological aspects be glossed over, and here

the bicycle has an immense advantage over any other form of transportin towns. The only possible emotional cloud on an otherwise clearhorizon can be discerned by close observation of cyclists passing busqueues-almost all will be seen to be looking straight ahead. Themore sensitive tend to look away, for, to those who have regainedtheir freedom of movement in cities by taking to two wheels, thesight of their still captive fellow citizens actually flaunting their chainscan be distressing. The problems of parking and traffic jams whichadd to the stress of the motorist trouble the cyclist hardly at all, andif he feels frustrated he can work it off through his pedals, which is ahealthy and proper occasion for adrenaline, hurts nobody, and getshim along even faster. His carbound neighbour has to sit tight andput up with it, and only the cigarette and tranquilliser manufacturersbenefit; his arteries and the National Health Service patently do not,for nervous tension and physical inactivity can be a dangerous mixturein the long run.But however phlegmatic the motorist may try to be, his car-for all

its impassive exterior-does get extremely hot under the bonnet.It explodes its air and petrol mixture at 2000-2250'C (2273-2523°K),'8and with end-products that are decidedly uncouth. In the dieselcylinder the maximum mean temperature is about the same, and thisis over one-third the surface temperature of the sur (60001C),'29 sothese ardent engines are, frankly, having to push it almost indecently

From the Memoir of Thomas Bewick Written by Himself1822-1828: "In passing through life, it has fortunately beenmy lot to have been intimate with both military and navalgentlemen, as well as with those of the learned professions;and, though several of each class have stood high in theestimation of the world, for their gentlemanly manners andunsullied worth-to which I may be allowed to add mytestimony, as well as to acknowledge the debt of gratitudeI owe some of them for their kindness and attention-yet,on taking a comparative survey of the whole, I cannot helpgiving a preference to medical men; for, besides theirlearning and attainments in common with other professions,they appear to me, generally, to be further removed fromprejudice, more enlightened, and more liberal in theirsentiments than the other labourers in the vineyards ofscience and literature."-Thomas Bewick (1753-1828) wasone of England's greatest wood engravers.


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hard to achieve satisfactory oxidation of their fuel. The cyclist'shandling of his air intake is altogether more discriminating andrefined, and he can slide oxygen into his working muscles at 37°C(310°K) without so much as a thought, using it there in completesilence and at full power with a rise in local temperature of only a

few degrees at most.

Getting the facts straight

But in getting his oxygen the urban cyclist does breathe in some

things that lie would rather avoid; and it is important here to get a

few facts straight, for it is widely and erroneously believed that thepolluted air of cities constitutes a particular hazard for the cyclist.Richard Ballantine, in an otherwise excellent and authoritative book,'0which is widely read by civilised travellers both here and in theUnited States, says that of the toxic chemicals in the air "the worstfor the cyclist are lead and carbon monoxide," and in the same

section we read, "One statistic is that the average urbanite inhalesthe equivalent in particles and poisons of two packs of cigarettes per

day. Does this translate for the bike rider as four packets of cigarettesper day? five ? six ?" A mind-boggling sentence if ever there was one.

Even the thought of mounting a bicycle makes one want to cough.Tobacco contains no lead, but I know exactly how many cigarettes

this "statistic" translates to in terms of carbon monoxide because Ihave measured it on myself, and the answer under average cityconditions in London is none at all. It is implied that the cyclist ismore at risk because he is breathing in harder and faster than themotorist, but he is also breathing out harder and faster, so that a gas

like carbon monoxide will equally be blown off more rapidly by hislungs as soon as he has overtaken or otherwise got away from theexhaust pipes that were polluting him. Even at rest, half the carbonmonoxide in our blood is breathed off in 4i hours.3" But how can

any urban bicycle rider sleep peacefully in his bed when he readsthis: "Carbon monoxide is the greatest immediate risk for the cyclist.It is a classic poison which interferes with the oxygen-carryingcapacity of the blood. Long before it kills, this action results indecreased alertness, headaches, vague dizziness and nausea. Thisdehabilitation adds to the hazard of traffic jamming" ?30

The lethal level of carboxyhaemoglobin in the blood is over 50%O.If this meant only 50% tissue hypoxia it could be supported, but itmeans much more than that because carbon monoxide shifts theoxygen dissociation curve of haemoglobin to the left so that whatreduced oxygen there is in the red cells can also less readily diffuseout of them. Most people who reach this level are not able to writeabout it afterwards, but J S Haldane took himself very near it in 1895during experiments on himself.32 He breathed 2100 ppm of CO for71+ minutes, and only after 34 minutes, when his COHb would havebeen about 25%0 ,31 did he note a "very slight feeling of fullness andthrobbing in the head." At 43 minutes, with a saturation of over

39%, he felt "decidedly abnormal, slight hyperpnoea, and markedthrobbing." He stopped the experiment nearly half-an-hour laterwhen his blood was 49% saturated, recording "vision dim, limbsweak. Had some difficulty in getting up or walking without assiszance,movements being very uncertain."32 A remarkably brave man.

We are much softer on ourselves nowadays, and the nearest

approach to these levels in contemporary society now that we no

longer use coal gas in our ovens is seen in the chain smoker, whosecarbon monoxide saturation may exceptionally reach 20%. Twopacks (40 cigarettes) a day fully inhaled may produce about 14%,but no non-smoker ever approaches these figures. Even for a policemanon duty for three hours at a busy intersection in still air the level doesnot exceed 3% ; for a non-smoking taxi driver it may occasionallyreach 2-5%; and for a motorist commuting for 15 miles it is about0-8-0-9%The measurements on me were done at the end of a morning in

which I had cycled 10 miles, the last six of which were in thick trafficon deliberately chosen main throughroads to end up in the City at

Smithfield in Professor Lawther's laboratory at the MRC ToxicologyUnit of St Bartholomew's Hospital. The level of carboxyhaemoglobinin my blood was then 0-3%. But it was a windy day, which meant a

lower level of pollution at ground level anyway, so I repeated thejourney on a day when there was no wind and the figure was stillonly 05%. This is no higher than a pedestrian's, and is within the

range found in all of us-even in the Outer Hebrides-from thenormal disintegration of our wom-out red cells, the carbon monoxidearising from the breakdown of the pyrrole rings in the nucleus of thehaemoglobin molecule.33

Similar levels were reported in a small-scale study of 10 young


healthy non-smoking volunteers set up by the United StatesDepartment of Transportation in Washington, DC, in 1977," duringthe hot and highly polluted evening rush hours of two midsummermonths. An unexpected finding was that the blood carbon monoxidelevels of these young men tended to be higher when they rode inair-conditioned cars than when they cycled, presumably because ontheir bicycles they were more mobile and able to avoid long waits intraffic.

This is not to underestimate the overall environmental impact ofCO, which, after carbon dioxide, is the commonest aerial pollutant-to the tune of probably 250 million tons (1 23 x 1012 kg) a year.3' Byfar the largest single source in recent times is the ubiquitous privatecar. The diesel engine produces very little, because combustion init is more complete. Carbon monoxide reacts with the iron in porphyrinand it therefore affects haemoglobin, myoglobin, cytochrome oxidase(cytochrome a and a3), and cytochrome P-450.3 It has an affinity forhaemoglobin which is about 210 times stronger than that of oxygen,so that if its concentration in inspired air is over 1/210 that of oxygenit will displace it from the red cells. Carbon monoxide has been aroundfor aeons and, in many ways, is a thoroughly antisocial smallmolecule, but, although it may cripple the smoker,'5 there is noevidence whatever that it harms the cyclist. Indeed, in the naturalworld, as opposed to the industrial, its production is probably theonly thing that man has in common with forest fires, some deep-seacoelenterates, certain higher animals and plants, and volcanoes.3'Our other main ogre is lead. Does the cyclist's deeper breathing

in fact cause him to absorb an unacceptable amount of this poisonousmetal which, unlike carbon monoxide, he cannot breathe off? Thefirst thing to be said about the lead in our bodies is, as ProfessorLawther points out, that the main source for most of us is not fromthe air at all but from water contaminated by pipes, food contaminatedby containers, and, to a minimal extent, from crops-and thereforemilk-produced near motorways.A lead level in adult human blood of over 80 micrograms per 100 ml

implies excess absorption. The level in London taxi drivers variesbetween 16 and 40," although the diesel fuel of their own vehiclescontains none. My own level is 18,ug/100 ml (0 8,umol/l), and Isuppose that I am a fairly average cyclist in that I cover about ninemiles each working day and 2600 miles a year, all in central London.Many maintain that the lead level in our petrol is a national disgrace,and it may well be, but the risk appears to be less to the cyclist thanto people-and particularly children-who have to live with constanttraffic past their doors for 18 hours a day.But what about the pollutants that we can see-the smoke which

pours from all exhausts and lines our collars and cuffs if we live inLondon? Particles of a size greater than about 5 are trapped by themucous sheet which lines our airways down to and including theterminal bronchioles, and ciliary movement carries this sheet at therate of about 2 cm a minute36 up to the throat, where it is swallowed.Cigarette smoke paralyses this movement, within seconds; thepolluted air of cities does not. So again, it is hardly fair to comparethe cyclist, his lung-clearing mechanism intact, with the two-pack-a-day smoker whose mechanism will be out of action for much of thetime, particularly when the tracheas of patients with chronic ob-structive lung disease have been found to have zones in whichmucociliary clearance is completely absent, whereas no such zonesare seen in the healthy tracheas of non-smokers.36

I feel a twinge of disloyalty in writing in this way about pollutionbecause there lives outside my house, or as near as it can get, aspark-ignition engine that has served me and my family withoutstint or complaint for over 10 years. But for the kind of short, lightlyloaded journeys that many people need to do in London, a car canbe a positive handicap sometimes, a hazard to health in the long run,and a great time loser. The cost in petrol alone had I crawled aroundin mine for my last 19 000 miles of visits would have been 760gallons, and that is an amount worth saving in anyone's book.The colossal amounts of liquid fuel at present being burnt in the

world by all forms of mechanical transport may well make it imperativesoon to consider which methods are unacceptably wasteful. ProfessorRichard A Rice has compared the net propulsion efficiency and fueldemands of a wide range of vehicles from helicopters, jumbo jets,and supersonic transports to motorcycles, cars, intercity trains, andbicycles.'7 Acar withonly thedriver in it uses seven times as muchfuel per passenger-mile as a double-decker bus with 20 passengers,(and 14 times as much as an Intercity express carrying 400). But, ofcourse, one has to catch a bus or train. A car is more personallyconvenient, but often less so than a bicycle which uses 50 times lessenergy. Professor Rice reached the conclusion that "the human beingand the bicycle are uniquely efficient as transport, and man's in-creasingly innovative devices are uniquely inefficient." He went on


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to suggest that propulsion efficiency would become increasinglyimportant as energy becomes more expensive, but no Governmentagency in Britain seems to be even remotely bothered by this particularquestion, although the economic, ecological, and atmospheric effectsof our colossal burning of fossil fuels are becoming increasinglyapparent. One of the most striking and well-documented environ-mental changes is the steady increase since 1900 in atmosphericcarbon dioxide.38

Sources of energy

It all boils down, of course, to our use of energy, and thereis no denying that there is a lot of it about. The question ishow we use it, and whether we tap it in forms which are non-renewable or which can be renewed. The bicycle is the onlyform of land transport in common use whose fuel supply isperpetually replaceable, and it is remarkably unspecialisedfuel at that: anything, in fact, from caviar to chips. Horse-drawnvehicles also run on replaceable fuel-although it is, by thelook of it, less varied. They appear in the main nowadays onlyon State occasions, but are sometimes used in central Londonfor the transport of ambassadors and beer.The sun is an exceptional source of photons, and as much

solar energy falls on the surface of the earth in two weeks as allthe energy contained in the world's initial fossil-fuel reserves.39The photovoltaic cell-which produces electricity-and thesolar panel-which produces heat-share with striated musclethe advantage of being clean and quiet, and we should probablybe concentrating more than we are on developing these,particularly as our local star is expected to keep up its presentoutput of energy for about another 5000 million years.2' Atomicenergy is certainly not clean and is by no means always quiet,and we still do not know whether our descendants will bless orcurse us for having tried to develop it.The annual mean power of the sun in southern England during

the hours of daylight is about 210 watts per square metre.39 InAustralia it is 400 watts, and the solar energy falling on thatcontinent in one year is equivalent to the total projected fuelreserves of the whole earth.39 A middle-aged Englishman ofaverage size sitting quietly in a deckchair on Blackpool beachand reading Paradise Lost covers an area of rather less thanone square metre. If the weather is warm his personal powerconsumption-which will probably be slightly above his "basal"metabolic rate-will be about 95 watts (95 joules/s, or 1-37kcal/min),' and it will not flicker much above this level solong as he keeps his eyes on his book and goes on readingMilton. If he feels-as well he might-an uncontrollable urgeto make for open country, he has only to increase his energyexpenditure by five times to get himself there on his bicycle atthe comfortable speed of 14 mph (upright), or 18 mph if hecan assume the more streamlined position of the racing Cyclist.3

It will be noted that although his total expenditure of energyat these speeds will be approaching f kilowatt, the actual poweroutput that he transmits to his pedals will be only one-quarterof the increase over his basal rate, for his efficiency in convertingchemical energy into mechanical work is, like that of frogs andtoads, about 250o040 This is rather better than his car's 200,0,and, as with the motor car, almost all the remaining energy islost as heat.19Homo sedentarius never lets himself get into a position like

this, and one of them-it sounds like Oscar Wilde or perhaps theAmerican Will Rogers, although I have not been able to trace thesource-has summed it all up with disarming clarity: "WheneverI feel the need for exercise I go and lie down for half an houruntil the feeling passes." He speaks for large numbers of thehuman race, many of them people of marvellous creativity-philosophers, scientists, painters, and poets-and we are all thericher for having them sitting around (some of them). Others,who sit on committees and keep behind glass and go chairboundin cars from one seat to another, are less life-enhancing. Overthem it is kinder to draw a veil, for although the sun shines on

them, too, on the rare occasions when they are out in it, obesityis a constant hazard and their horizons do become limited.

It is indeed a sobering thought that these enclosed andcushioned bipeds will have entered adult life with about 40%of their total body mass in the form of muscle,26 most of itdisposed for the working of their limbs. But this superb endow-ment, deprived of even token care and maintenance, hangs idlearound his thinning bones as Homo constrictus struggles toemerge, his mind on other things. Conditioned to his car,constricted in movement, outlook, and arteries, he is piteouslydependent when it comes to urban travel, and often very slow.The cyclist, on the other hand, can move in towns with a

facility that is denied to those who cannot contemplate travellingany distance without paying to be moved. The fuming stillnessof the traffic taxes him little, and a grateful government doesnot tax him at all. He is one of the few wheeled travellers in themodern city who is not roofed in, and if he looks up on somenights he may even see the stars. Like the runner or the climber,he has the rather special satisfaction of competing in largemeasure against himself. In no way is this masochistic; it can, infact, be sheer delight and derives, I suspect, from deep in ourprimal consciousness, perhaps because only those who coulddo this survived.

It redresses our urban imbalance to propel ourselves onoccasion, to move in the open under the sun and encounter thewind and the rain, or ride noiseless under the moon, to retain atleast some links with our natural environment and our longinscrutable past, and to keep in perspective the nagging demandsof our taut metropolitan minds. Our descendants, too, will needto do this if they are to keep themselves contented on this earthand not become the slaves of their technology-paddedpassengers of societies in blinkers without direction, light, orhealth.

In part the cyclist steers clear of this risk and provides somesort of a solution. He has, of course, the advantage of biochemicaland neuronal systems developed over 500 million years42 andtested, often to destruction, under the most rigorous conditions.He moves easily, intelligently, and cleanly about his city orcountryside with an energy expenditure equivalent to over1400 miles to the gallon (495 km/litre). His freedom is immense.He combines a relatively simple- machine with a propulsionunit of quite incredible functional elegance, and in the leagueof all movers-caterpillars, comets, or Cadillacs-there isnothing to touch him.

References1 Wilson, S S, Scientific American, 1973, 228, No 3, 81.2 Bekker, M G, Theory of Land Locomotion. Ann Arbor, University of

Michigan Press, 1956.3 Whitt, F R, and Wilson, D A, Bicycling Science, Ergonomics and Mechanics.

Cambridge, Mass, and London, MIT Press, 1974.4 Swanison, S A V, personal communication.5 Cooper, K H, The New Aerobics. New York, Toronto, and London,

Bantam Books, 1970.6 Durnin, J V G A, and Passmore, R, Energy, Work and Leisure. London,

Heinemann Educational Books, 1967.7 Rashevsky, N, Mathematical Biophysics. Chicago, University of Chicago

Press, 1948.8 Swanson, S A V, in Adult Articular Cartilage, ed M A R Freeman.

London, Pitman Medical, 1973.9 Maroudas, A, in Adult Articular Cartilage, ed M A R Freeman. London,

Pitman Medical, 1973.10 Maroudas, A, Nature, 1976, 260, No 5554, 808.

Department of Transport, Road Accidents in Great Britain 1975. London,HMSO, 1977.

12 Department of the Environment, Transport Policy. A ConsultationDocument. London, HMSO, 1976.

13 Hudson, M, The Bicycle Planning Book. London, Open Books/Friends ofthe Earth, 1978.

14 Passmore, R, An Assessment of the Reports of the Second Committee onCalorie Requirements (FAO 1957). Rome, Food and AgricultureOrganisation of the United Nations, 1964.

15 Durnin, J V G A, in the Physiology of Human Survival, ed 0 D Edholmand A C Bacharach. London and New York, Academic Press, 1965.

16 Wood, P D, et al, Metabolism, 1976, 25, 1249.17 Williams, R E, British Medical)Journal, 1975, 4, 25.


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18 Carlson, F D, and Wilkie, D R, Muscle Physiology. New Jersey, Prentice-Hall, 1974.

9 Astrand, P 0, and Rodahl, K, A Textbook of Work Physiology. New York,McGraw-Hill, 1970.

20 Dubowitz, V, and Brooke, M H, Muscle Biopsy: a Modern Approach,p 44. London, Saunders, 1973.

21 Gollnick, P D, et al,J7ournal of Applied Physiology, 1972, 33, 312.22 Costill, D L, et al, New York Academy of Sciences Conference on the

Marathon. Abstract 246. 1976.23 Anderson, P, and Hendriksson, J, J7ournal of Physiology, 1977, 270, 677.24 Bergman, H, et al, European Journal of Clinical Investigation, 1973, 3, 414.25 Young, A, in Cycling-the Healthy Alternative, p 12. London, British

Cycling Bureau, 1978.26 Edwards, R H T, Clinical Science and Molecular Medicine, 1978, 54, 463.27 Young, A, personal communication.28 Obert, E F, Internal Combustion Engines and Air Pollution. New York,

Intext Educational Publishers, 1973.29 Lancaster Brown, P, Astronomy in Colour. London, Blandford Press, 1972.30 Ballantine, R, Richard's Bicycle Book. London, Pan Books, 1975.31 Lawther, P J, British Medical Bulletin, 1975, 31, No 3, 256.

32 Haldane, J, Journal of Physiology, 1895, 18, 430.33 Lawther, P J, personal communication.34 Messer Associates, A Study of the Health Effects of Bicycling in an Urban

Atmosphere. Prepared for the Office of Environmental Affairs, USDepartment of Transportation. Springfield, Va, National TechnicalInformation Service, 1977. Reported in Science, 1978, 199, 1187.

35 Astrup, P, Kjeldsen, K, and Wanstrup, J, J'ournal of AtherosclerosisResearch, 1967, 7, 343.

36 Santa Cruz, R, et al, American Review of Respiratory Disease, 1974, 109,458.

37 Rice, R A, Technology Review, 1972, 75, 31.38 Lamb, H H, Climate, Present, Past and Future, Vol 1. London, Methuen,

1972.S9 Archer, M D, Futures, June 1974, 261.40 Wilkie, D R, Muscle. London and Beccles, William Clowes and Sons.

1968.41 Angrist, S W, and Hepler, L A, Order and Chaos, Laws of Energy and

Entropy. New York, Basic Books, 1967.42 Primitive snail-like creatures were well established by the end of the

Cambrian period. The Geological Museum.

The spirit of occupational medicine

DOUGLAS BLACK

Before I disclaim anything remotely approaching skill (con-vincingly, I imagine), I should like to declare a genuine interestin occupational medicine.* This might be said to go back along way, for the first patient whom I ever clerked in Dundeewas a gill-filler in a hackle works; and a seaport full of jutemills could scarcely fail to arouse curiosity about the effect ofoccupation on health. But the experience which, to use a cantphrase, really turned me on to occupational medicine wasreading Donald Hunter's Lectures on Occupational Diseases-the slim precursor of The Diseases of Occupations. In Oxford Iworked in the same firm as Richard Browne, who alerted me towhat was later to become ergonomics. The plasticity of man'sperformance is great; but it should not on that account beabused by correctable faulty design in the equipment which hehas to manipulate. Throughout my years in Manchester I hadas successive colleagues Ronald Lane, Tom Scott, and TimLee, from each of whom I learnt much; and, of course, RichardSchilling spent some years in Manchester before coming to thechair at the London School of Hygiene. So I think I can claimto have been in good company, and my lack of any contributionto occupational medicine must be my own fault. Nevertheless,I am proud that circumstances enabled me to be, if not aproper midwife, at least a Sarah Gamp at the birth of the newfaculty.These days I am often constrained to break at least one of the

Duke of Wellington's two precepts for public speaking: "Inever speak of what I know nothing, and I never quote Latin."As I survey my response to my present commitment, I amreminded of the words with which Benjamin M'Cready openedhis prize dissertation for 1837, "On the Influence of Trades,Professions and Occupations, in the United States, in theProduction of Diseases." To quote, "The writer of the followingessay is aware of its numerous faults. He knows that his state-

*Based on the Lucas lecture given on the occasion of the first annual generalmeeting ofthe Faculty of Occupational Medicine, Royal College ofPhysicians,on 1 May 1979.

Royal College of Physicians, St Andrews Place, London NW1 4LESIR DOUGLAS BLACK, MD, PRCP, president

ments are often too general; that many of the points touchedupon are imperfectly treated of, and that others, equally be-longing to the subject, have been wholly neglected." He goeson to lament the absence of statistical data, forcing him torely on information from workmen, who, he alleges, "areso little attentive to the causes which affect their health,

Benjamin William M Gready

and their views are so often warped by prejudice orinterest, that little reliance can be placed upon them." I fearthat neither of these excuses for imperfection will avail metoday. Statistical data abound, in the Registrar General's returnsand elsewhere, and workers are no longer indifferent to factorsaffecting their health, as witness the TUG Centenary Instituteof Occupational Health in the London School of Hygiene.


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sanitate urbanorum · desanitate urbanorum ronaldwilliams the cities of the plain have always had...

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