278 - bmj military health · '278 physical exertion, fitness and breathing.l by henry briggs,...

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PHYSICAL EXERTION, FITNESS AND BREATHING. l

By HENRY BRIGGS, D.Se.,

Profe880r of Mining, Heriot-Watt College, Edinburgh.

THE experiments discussed, in this pape'r were carried out during the research OD mine rescue apparatus which was instituted in 1917 by the. Scientific and Industrial Research Department.2 Their aim at' first was limited to tl;tat of determining the oxygen consumption 'of persons engaging

· n differeR,t kinds of physical work,and with that object in view,a few'. · tests were made by Dr. J. S. Haldane and the writer on miners climbing i~clines in the Newbattle and Lingerwood collieries, Midlothian; these were shortly afterwards. supplemented by other tests on the same men in which. weights were lifted and certain of the common tasks of the miner were performed. During th~ early trials the men breathed ordin~ry air; but as the wearer of a, mine rescue apparatus has to breathe air ~ighly enricheQ with oxygen it was judged necessary to study ~he influence of

,_ such air on a person's capacity for physical work. It had' been a matter , of experience to the members of the Research Committee that they could

perform work with greater ease and comfort while wearing a rescue , apparatus in good order, and thus obtaining air ,9ontairiing 'seventy or

eighty per ce~t of oxygen,than under normal conditions. The writer, for I example, can climb a mountain faster and ·with less / fatigue when using .an

efficient mine rescue apparatus than without it, notwithstanding that the apparatus weighs, in its latest form', about thirty pounds .. It ,was observed that an increased o,xygen proportion in the air inha~ed was uniformly helpful_with persons of sedelJtary habits,but that when working miners were tested little or no such benefit was derived; / they were in fact generally quite indifferent as to whether they breathed air or oxygen.,

A long series of experiments was then commenced in which Martin's · ergometer was principally' used as the means of measuring the rate .of exertion, and in which a quantitative.and qualitative examinatioIl was made with subj~cts of vari()usphysique . and trai.ning breathing. air, and· oxygen. ThanksJo the kindness oC the Superintendents of Pbysicaland, Bayonet Training, Scottish Cqmmand and Aldershot, several soldiers specializing in different branch of athletics were included in the tests. .

I Reprinted from the Journa~ of Physiology, vol. liv, No, 4, 1920 .

.. The Research Oommittee consisbsof Mr. William Walker, O.B.E., H.M. Ohief Inspector of Mines (Ohairman), Dr. J. S. Haldane, F.R.S., and the w,rfter. Summaries of these experiments have been published in the writer's paper on "Fitness and Breathing during Exertion," Jotlrnal of P!tysiology, 53,J'roc. Physiol. Soc., p. 38, 1919, and in the Second Report of the Mine Rescue Apparatus Research Oommittee, 1920..

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Henry. Briggs 279

Subsequently, when it had become clear that' the fitness of a subject could be measured by contrasting \ his respiratory __ performance when breathing normal air, and when breathing el!riche,d air,the Army Council, acting upon the recommendation of Colonel Sir IWilliam -Horrocks,

- , K.C.M.G., C.B., and Lieutenant-Colonel E. P. Cathcart, of the Army -Medical Department, set up a physical test station at which, up to th.e Armistice, the ,new method was applied for the examination of men sent in from units under 'the Scottish Command. . - / -

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APPARA'l'mi A,ND METHODS.,

The ergometer experiments 'were carried out in the Ileriot-Watt College, Edinburgh,·with·Mm·tin's ergometer [lJ. During th~ experiment,s a' pendulum, hanging in front of the subject 3.she sat in the saddle, provided the means of timing the rate of revolution of thepedals.1 A rate of fifty-six revolutions per minute was adopted throughout. At that speed, and with the gear-ratio of the particular cycle employe'd, the power expended, in foot-pounds per minute, was ascertained by multiplying the

, difference',of the balance-readings, in pounds, by one thousand. , Mete1's.~TwoMilne dry meters were used. In _ each of them one , revolution of the eight-inch pointer indicated the:passage of one cubic foot _-'of gas. , The 'dials were .marked offin hundredths of a cubic foot. The meters were t~sted against displacement from time to time. ''J;'he'baromettlc pressure, temperature and hygrometric state of gas being metered were kept llnder .observation." -, Douglas Bag and Sampling Apparatus.-A sixty-litre wedge-shaped bag was used to collect expired ajr. The bag, which is part of the Douglas respiration apparatus [2J, is 'provided with a three-way aluminium stopcock which allows of the expired air being either disch~rged direct to the atmosphere (" off" position) or into the bag ("'on" position). A small rubber tube connected to the bagenables samples of the contents to be drawn off for .analysis. At first ghss sampling tubes with taps at each end were used for this purpose, but they were soon abandoned in favour of sinall well-stoppered bottles, filled over a mercury trough. In the large numbers required the bottles were handier, simpler to use, less costly and -much more easily, replaced in case of breakage. A further simplification in taking samples for analysis was introduced at the Test Station.

Oxyyen Cylinders and Reservoir Bag.--'-When the subjec,t was breathing oxyg~n the gas was supplied from a lOO-feet cylinder fitted'witha reducing valve. The oxygen discharged from the valve into a reservoir bag. At

, first the subjects complained of parching of the throat when breathing oxygen; the trouble was removed by causing the' gas to bubble through wat,er before entering the reservoir. The latter was kept about three

I, For long-continued, pedalling the pendulum is -preferable to the metronolne for this purpose; it is less trying to the nerves. -

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280 Physical Exe1',tion, Fitness and B"eathing

parts distended during a "run." Over-distension wa.s carefully avoided, as with excess of pressure in the reservoir bag it became possible for the gas to push open both breathing valves and to discharge direct into the Douglas bag.

Mottthp'iece, Valpes and Tubes.-The subject used a, rescue-appal'atns moutbpieee of rubber which fitted over one limb of a met,.1 T-piece. The nose was closed by a clip. 'rhe air was directed to and from tbe mouth· piece by inspiratory and expiratory valves. Various valves were tried, the most successful being tbe Mueller water val ve (fig. l) and the Rosling valve (fig. 2). A Mneller valve of the dimensions indicated in fig. 1 allows of ' the heavy breathing of severe exertion without introducing a degree of resistance appreciable to most persons.

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FIG. l.- Mucller Wa.ter Valve. FIG. 2. - Rosling Va.lve, shut and open.

The Rosling valve, adopted towards the end of the war for army antigas purposes, is very free from resistance and low in slip. ,Vhile Mueller's is only serviceable for a stationary subject in tbe laboratory, Rosling's is equally useful in the laboratory and in testing men marching 01' climbing in tbe open or in tbe mine. Unlike tbe mica disk valve so frequently used in respiration experiments, it functions properly in any position. The valve is of rubber. A tbin square of rubber, holl! by the corners, closes upon the Hanged end of the tubular part of the valve (fig. 2, left-hand view) and flexes away from it when allowing ail' to pass througb (fig. 2, rigbt·hand view). The valve here illustrated was made for tbe writer by tbe Islewortb Rubber Company and adopted in the Briggs Mine Rescue Apparatus. Its resistance to a flow of eighty-five litres (three cubic feet) of air per minute is 0'35 inch of water column, and its slip is quite negligible. A not unimportant feature of tbe rubber valve is its noiseless·




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Henry Briggs 281

n~ss. ' When a valve makes a distinctive noise the subject's 'attention is apt ,to be directed to his own breathing, ,and the test may be vitiated t:pereby. The tubes le8,ding to and from themoutbpiece were of one inch bore-a size sufficiEmt to redu~e their resistance to negligible magnitude even with hard panting. '" :

'Sampling Ttibe for Alveolat· Air . ...,;,..,A number of samples ,of alveolar air , were taken while certain' of the' subj~cts were pedalling the ergometer. , Essentially, the apparatus used for this, purpose was that de,scribed by

Haldane and Priestley' [3J ; ~t, consists of a long, tube through which tre subject can empty his lungs suddenly. 'To avoid, the subi,ect having to I

close ,the ,end of, the tube with, his tongue after such an expiration, as was done in 'Haldi1lle's and Priestley:s experiments, a, wide-bore tap was fitted at that end; on this being closed the, man cO~lld replace the rubber, mouthpiece' '(which for the moment' he had withdrawn) and continue working, ,leaving the experimenter to 'draw out Jrom behind the tap a small sample of air for analysis. 'With the quickened breathing incident' tophysiQal work, it w'as not possible' to get alveolar air samples after

, inspiration and after expiration as maY,be done under rest conditions. ' Most of~ the experiments were on blen altogether strange, to scientific methods; few ,were, suffiqiently trustworthy when, it came to the difficult operation' of providing 'a reliable alveolar sample while doing hard work. -

G.as-analysis Apparatus.-'-In the 11l1i.in set of experiments, in, which both oxygen and carbon dioxide were determined in each sample of expired air, the Haldane gas-analysis apparatus [4J was used. At the test station,

, where the routine was siQlplified and only CO2 ascertained, the Briggs' apparatus [5]' was adopted.

Manner of Oonducting Experiinents.~A number of preliminary trials were carried out in order to settle such matters as the rest perio4 need,ed between spells of work 'on the ergometer, and the length of' time work must continue before the'breathing becomes sufficiently en rapport with _ the exertioI! to permit, of reliable observations being made. After tha:t, a regular routine, based on Douglas; method,','soon evolved, and the few cha'nges- subsequently made' were' merely to simplify the apparatus and connections and to improve the valves. This, routine was as follows,:- The subject, seated at rest on the saddle of the ergometer and fitted with, the noseclip and mouthpiece attachment, inhaled air from'the room, drawing it through one' of the Milne meters; The Douglas bag (now empty) was

, connected to the exhalation tube with the three, way cock in the " off" - ,/ ,position to allow the -products of respiration to escape into the room. When he had become accustomed to his position the cock was turned « on " at tp,e end of ~an inspiration and the expi,r,ed air began to enter the bag. A stop wat~h was _started at the moment of turning the cock, and the number of inspirations was counted by watchirig the movement of the pointer of the meter. A.ftetabout two minutes had- elapsed, and again at the end of an inspiration, tbetap- was turned ." off," and the watch

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282 Physical Exertiqn, Fitness and Brep,tMng

stopped. The bag was kneaded and one o~ i'nore samples drawn from- it. The vol'ume in the bag was then measured 'by emptying the -bag_through, the second meter. The n:ece~sary thermometer and 4ygrometer readIngs were taken. From these mea~urements and the time i.nterval the volume exhaled per minute w:as calculated. The meter. on. the inspiration side en~bled the quantity <Jrawn into th~ lungs to b~ evaluated direct. Owing to the jerky action of the latter meter this determination did not reach the sa~e degree of accuracy as, that of. the volume of exhaled air from the Douglas bag, but it 'Yas useful as a safeguard, against gross error.

The seconp. set of readings and samples were taken when the subject -was pedalling with the belt off, i.e., when he was doing no ~xternal work. - The'same' routine was followed, the man being'required to pedal at the.

rate of fifty-si)\. revolutions per minute for at least two minutes before com.! mencing to collect the' ex'pired air. After this, similar· records 'were

,obtained' with grad'ually increasing loads; - Longer'rest intervals :were allowed between the spells of work as the loads inc,re-as-ed. The preliminary· _,

,interval of- .two minutes' pedalling was strictly oBserved" except for- the , highest loads, such as 1'2,000 or 14,000 feet pounds per 'minute, which are'

beyond the capacity of even the strongest men to sustain for long. \Vith excessive loads the -prelimihary interval had perforce to' be' shortened,

_ though it was never allowed to be under one minute.. The reduction of that interval, however, makes the determination of oxygen-consumption, etc., on the highest loads less r~liable than those on more moderate rates of work" a fiatute which receiv~s further consideration below.-.

After making a series of measurements with the man breathing air, . ail exactly similar series .was made when breathing oxygen. Before commencing the latter tne subject was required to breathe oxygen for at least ten minutes to expel the greater part of the nitrogen dissolved in the blood. The interval between, the ~irand oxygen tests was u~ually some -hours; on several occasions, tbe two series· were carried out on

, d~fferent days. In the case,s of several of those tested at the college, and of nearly alrthose tried at- .the test station,- no inf~n~ation was given to the subject ~s to whether he was breathing o~ygen or air: . It was-thought best not to give a loophole for the prejudice, which is still curiousfy strong. against breathing oxygen for,a few hours. I ;;.

After a few tests with a simple pneumograph it was abandoned. AI'? . has been stated, the rate of breathing was ascertained by watching the -

.. pointer of the meter on the inspiration side, and as the met,er h~d its back to the suP.i~ct, he was-generally unaware that any notice was being taken -of his breathing.' '. • ' '

, " ERGOMETER 'TESTS: '

Figs. 3 to 14 (see end Of -this paper) ar~ typical graphed' records of subjects undertaking work on- the ergometer in the manner' described:. The small 'circles on the charts indicate values obtained when the men

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Henry Briggs 283

were, breathing normal air and the crosses thqse obtained when breathing oxygen; the more-or-less smoothed ,', air "curves are drawn in full lines

"and the "'oxygen" curves :in dotted lJnes.Th~ 'output of CO2 and the Oxygen cOlfsumpiion ar,e set out)n litres per minute of dry' gas at N.T.P. ,The volume venti'lating the lungs is given in htres of saturated air or', oxygen a.t blood temperature and normal pressure, expired ,per minute. The Qxygen consumed was computed from the respiratory, qUdtient and the COzoutput,. "",'" , " The determination of the'respiratory quotient by gas-analysis depends on the assumptirm that'the mass of nitrogen inhaled is the s'am,~ as the mass of nitrogen exhaled. 'the nitrogen; in fact, serves here as a measure or standard against which variatiops in oxygen are gauged. Evidently such a process will beniore accurate wpen the nitrogen, as iri ordinary air, exceeds the oxygen in volume: i.e. when the smaller is gauged, by the greater; It will be les,s accurate when the nitrogen proportion.is much lower than that of oxygen,as 'when cylinder oxygen is 'breathed, for then the greater ,is g~uged by the lesser., As might theref0re be expected, oxygen consumptions, calculated in the manner indicated, from nieasurementsmade when, bre~thing cylinder oxygen, had a relatively high probable error. Another method ofeva,luating oxygen consumption was, however, applicable, owing to the volumes inhaled and exhaled being separately me~sured; and in case of doubt this second method was used as a check. It consists of finding (a) the volume of oxygen en:tering the lungs per minute (from the' v()lume of enriched air inhaled and the proportion of oxygen,in that inhaled

,gas) ; (b) the volume of oxygen l"eaving the lungs per minute (from the volume expired per minute and the proportion of oxygen in the expired air), when the difference (a)-(b) gives the required result. "

-, Towards the'end of the, main series ,of experiinen,ts it was found that, even in 3., subject of Iow fitness, no adva~tage was to be 'secured by , increasing' the' percentage of oxygen above, sixty. Had"that fact ,been known earlier, .the work ,would have been facilitated by using,a mixture ,containing sixty per ,cent oxygen and forty per cent nitrogen in, place of cylipder oxygep; the higher proportion of nitrogen which would then nave been available would have reduced the probable error of the oxygen. con~ ,sumption determinations on enriched air. At the ,physica1test station sixty-seven per cent of oxygen was used instead of cylinderoxvgen.-

It has sometimes been advanced as a dra,5Vback to the Douglas method that,the sample of exllaled air collected in the bag is contained over too short a period.' :For_work of the character 'now being considered', how'ever,

'the criticism I would not appear t<;:> ha~e much 'Yeight: If elementary precautions are taken, such as that of opening and closing the bag at the

, same stage in the breathing (e,g.'at the end of inspiration), the shortness of the' period of. collecting . th~ expired air is not a matter of conseq]1ence; of much great~r importance is the length of the preliminary period during

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284 Physjca,l Exertion, Fit_ness a~d Breathing

which the mail is required~o work before the expired air is allowed to ,enter the bag. This should be uniform and adequate.

It was not practicabl~ to put the subjects on a definite dietary. While this increased the' degree of uncertainty of any single pair of observations',

. it does not affect the general result~, since a large number of men were tested, and ,vhenever doubt was felt in regard to the reliability of ~a set of nieasurements, the test- wag. repeated on' another day. , Normal and'Ove1·load.-Every-day experience proves. that.a muscular

performance is .easier when one is in'" good condition." Equally-common-place 3;~e the facts that no task involving .external work, not even the lightest, can ..... be continued indefinitely· without pause, .and that the heavier' the work the, shorter the time it can be sustained: There are., however, certain' lesser d~gt(3es 'of exertion (fo~ instance walking' or cycling at a ,moderate pace on 'a flat road), which, by the ease with which they ,/ can be kept up for, hours on end, may be referred to,' in . ~lectrical engineers' phraseology as "normal 10aC!.s "; while other and heavier tasks· (e.g: hard baY9net exercise m: running quickly upstairs) are bearable for" I

a limited.period .only and may be termed" overloads." ,What may be an overload to one 'person is a normal load to another .who is stronger; or who is in better training or more habituated to the' particular kind of labour. Again, a nQrmalload when the person 'is fit may prove to be,an ov.erload when' he is unfit; and, as has been remarked, ,even a light'

'normal load if long supported without rest will eventually become, an overload. Evident1y,. then, the whereahouts of the line demarcating between a no);mal and an overload .for .'any individual dependS on his' condition at the time; if he is getting tired, it 'is, 'moving down the scale of exert~on; if resting it is mov~ng up. . , . Oxygen Supply and Carbon Dioxide Output dut'ing Work.-:::-Ap"importan.tdiffer(:lnce between what we here 'term the normal load and the overload lies in their effect on the respiration after ~toppingthe rxertion. When one cease.s an easy normal load like walking at three miles per hour al:ong " a flat road, the breathing quickly adjusts itself to the resting state:, th~ after effectin a healthy person is nil. The influence of a sever~ overload is in ~a-rked contrast to this;· when 'tne work', is stopped heavy breathing continues; th~ lung-v'entilation falls to normal only after a period, whic~, in the~,case o( a hard spell of work, may b,e D:lfmy' hours. In the first instance the oxygen intake was adequate; in' the sec'ond it was not. Essentially, then,a·normallOad may be defined as one during the performance of which the oxygen supply is sufficient, and 'an overload one during'which it is,insufficient to satisfy in full the.demands of the working nluscles. - .

It is' obviou~ that the supply of oxygen to the'tissues may he deficient either in consequence of insufficient absorption in the lungs or inadequate circulation. Instances in which distress is produced by the rate of oxygenation of the blood failing to ke'ep pace with the muscular demands,

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Henry Briggs 285

though the circulation maybE) sufficient, are of great, practical interest. They include the case of the poison-gas patient, where exudation and thi~kE:ll1ing of the tlPitheliallayer of the .lungs makesoxyge~-penetration difficult,; t~e case of the high-flying airman, wnere the low partial pressure of 'oxygenprevents proper oxygenation of the blood, and that of the

, so-called D.A.H. patient, where theshallo~ness of -the breathing Impairs the transfer of oxygen to th~ blood by insufficient exposure of epithelial area to freshly illdrawn air [6]. - __

. lA glance at the' accompanying char·ts will show" that when hard muscnlar work is being done the consumption of oxygen may rise to more than ten times the resting value. ' 'In,',t,he muscles at work there must be a much greater proportional increase of consumption, and such an increase can only be secured by an enormous addition to the blood 'circulation through those muscles. Failure to supply the add,itional blood;' whether due to defects in blood-distribution or to cardiac efficiency, must, therefore, bring about locaL anoxremia in the muscles, resulting in a' c.essation or reduction of the exertion. .

Now it is known that, when muscles' are insufficiently -supplied with oxygen, lactic aci!i is 'formed; indeed that when an extreme overload is' attempted, such as runtling qUIckly up several flights of stairs, the blood ~ is at once:f.l.ooded with lactic acid. The· highlystiml-ilative influence ,of lac~icacid' upon the respjratory centre and the relative slow rate at which it disappears from the blood are also well known. The formation of this acid would therefore appear sufficierit to account for the falling off of the percentage of CO2 in the expir.ed air whiqh (as the ,ourves show) is the invariable rule when the load is ipcreased b{3yo~d a certain amount, ~nd would also partly. explain t4e long continued,enhanced breathing after the ,cessation of a heavy overload'., . '

Since the appea.rance of lactic acid in the blood is ,a sure sign of . overload,' and since that appearance - is charac,terized by a fall in the proportion of CO2 expired, the writer feels justified in, taking the rate of work corresponding to the maximal CO2 proportion in the' expired 'air

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as the boundary between an overload and a normal load, while breathing air 'or oxygen as th~ case may be. This boundary, it will be understood, can only be a rough one. Nor is it a stable one; fatigue moves it down the scale. Again, ~the fact that in most cases (e.g. fig. 4) the expired-C02-

percentage curVe gradually flattens as the crest of the dome is approached, appears to ,denote the onset of oxygen-want before the "'crest-load" is reached; but since that influence '(except in th~ immediate regi.on of

, the crest load) is not usually serious, tQ..e subjec,t can support .such rates' - o£exertioil for a 'considerable time. In. other words, though there is

in ,the' charts good' evidence that (he call for oxygen by the working. muscles becomes (either per se or through th~ agency of lactic acid) a partner in respiratory control even on relatively light exertion; the demand appears to be satisfactorily met until the rate of work. is increased' up to, or. nearly up to, what is here·ter.med the 11 cres·t load.'" ,

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'286 Physical Exertion, Fitness and Breathing

Stam~na.-Stamina is taken·-to_ mean the power of supporting continuotis exer~ion.· It wili be apparent . that the higher the "crest load" the larger will be the range of loads which, can be gea~t wi~h without oxygen-want bringing the exercise to. 'an end. A given rate of work

. may be a normaf load to 'one man whose "crest load" is high and an overload to another whose" crest ,load" is low. Thus the crest load (the ' abscissal position of the crest of ,the dome of the exhaled-C02-percentage curve) becomes a measure of the stamina for the particular kind of work '. in question. .

In every case but one (Subject VIII) the. crest 'lpad was higher (i.e., the crest was' further to -the ·right) when breathing oxygen than when breathing air. In. most cases, that i~s to say, the· boundary between normal and overload moves up the scale, ',and, the subject,'s capacity for sustaine-d exer.tion is improved, as tbe partial pressure o,f oxygen in the irihaled air, and, therefore, in the alveolar air, is increased: The lower the person~s fitness the greater the improvement brought about.

. Alveolal'COz during ,the ,Accelerat~ve Period.-As has already been stated, a rate of work' like 12,000 ,foot-pounds per minute, was too' heavy to

,be :k~pt up long by any of the men tested, and on' sucb loads it was not possible 'to wjLitthe usual' two' minutes before taking the samples and readings. The result was-that on the heaviest loads, the latter were taken during the accelerative period. In some instances (Subjects' IT, IIl, IX, XIII, XV), alveolar samples were obtained during that period, and the CO 2 percentages are shown on tbe graphs. They will be seen to be unusually high; ,indeed with Subject XIII,preathing air,the record,figure of 10'1 per cent is reached. The matter lay outside, the, scope of the research and was not pursued further; but it would seem questionable wheth~r these high CO~ tensions are possible in the alveolar air without

I active excretion of CO 2 on the part of the lung-epithelium. Fitness and.Exp;il'ed.C02 Percentage.,The. graphs ma.y now be examined

with a view to aSyertaining the influence offitness on respiratory behaviour. The .high level of the CO 2 percentage in the air expired, by most fit

persons doing work is perhaps' the first featu.re 'to attract ~ttention. It is a usual 'but not an invariable attribute of. the fH man th'at he -can stand a' higher CO 2 and a lower pxygen percentage in the alveolar air

,than the unfit .man performing the same task;. he lllakes more use of the air he inhalE;ls and therefore !equires less of it. -'l'hus,.in contrasting' . the very striking at?le~ic; subject XIII (c.ondition (A) fig. 10) with the sedentary Subject II (fig. 4), when both are breathing normal air, the

I maximal CO2 percentage in' the 'former case is Seen to be 8'1 anq. in the latter case 4'7, and, although the heavier, man, XIII can work.the; ergometer on a lung· ventilation of less than half· that required by lI. The highest CO 2 and lowest oxyg'en-propottiollS were recorded in the case of those to whom slow, deep breathing is habitual during pbysi.cal'

, exercise. While working· at the-rate of 6,000foot-pi::>unds per minute/for.

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example;II breathed twentY,-four times per minute, while two unusually Ideep breathers, Nos. XIII and VIII, !espired eight times and twelve timfls ~ per minute respectively on that load. That the correspondence of high fitness ,and a high CO2 level is not invariable is shown by a subject' (graphs not reproduced), a ,very, fit young, athlete, 'whoseexpired-C0 2 -percentage reached it maximgm of only 4'8 when breathing oxygen. '

Fitness; Measurement.---,.Perhaps the Illost interesting alld useful 9f the results ,obtained follows from a corpparison of the curves of exhaledCO2-percentage when the subject breathes air and when' the subject breathes oxygen. Iri the case of a r{llatively unfit man, such as n, these curves diverge; but' in that of. VIII, (fig.8)~an' Army instructor .ill physical drill- sel{lcted for experiment by: the Scottish Command' as representing physically the best the Army can produce-the curve~ are almost coincident and their crests actually coincide. . Observations on n:Hi.njr'subjects have warranted 'the conclusion that fitness i~ inversely as the degree of divergence of the two CO2 curves. The most cOllveniellt manner of evaluating ,fitness proved to be the following: having drawn the two contrasting curves {work done, abscissre; CO2 percentages, ordinates} the expired-C02-percelltage, with the subject at rest and breathing normal air, was marked by an arrow-head on the Y-axis of the graph. A horizontal line havipg then been struck across' the chart' through the arrow-head" the vertical distances between that line arid the crests of the "air "and '~oxygen" curVes were measured off, The fitness factor was then taken to 'be the first of these distances divided

: by.the second. By this method the fitness of' Subject' II was 46 per, cent and 'that o~ VIII was 100 per cent. The factors, for the other selected subjects are stated in the Appendix., '

Th.e assumption underlying this ¥lode of, expressing fitness is tWofold,: ' first, there'is, as basis, the conception of zero fitness as being the state in which the CO2 curve oil air faHs away from the Y-aiis, or, in other words,

. in which the crest lies on that axis at a poiiit qoincident with the resting value of the CO2 percentage. That is to/say, zero fitness is regarded as the condition in whIch the slightest load is an overload and where oxygen',' want becomes serious when the least exertioQ is attempted. Secondly, there is the assumption that breathing oxygen raises' fitness (as regards the lutlgs) to 100 per cent .. The first point will be readily conceded; as to' the second, the evidence appears, conclusive. Subject III was tested on occasions several months apart '; the first time he was in low health and hIS fitness factor .was forty-four per cent ; the second time he was well and the factor had risen to eighty per cent; but the COg curve on o~ygen was substantially the same in each cll;se. Subject XIII was frequently tested

'over.a period of six months. At first ,he was in ilOrmal health and haq a fitness of seventy per cent. He wa,sthen sent to Aldershot for ~the final

'course .of'training for serjeant-instr,uctors in physibl drill and returned 'to ' Edinburgh in the "ipink" of' condition, 'for further test after being a

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fortnight' at Ald~r'shot. It was then found tha,t while the ,,' oxygen .. curve was suqstantially as before, the "air" curve had risen to meet it, and that; indeed, the two curves agreed up to the crest. In other words: fitness had become 100 per cent. Some, time after, XIII was. transferred ,back to Scotland under medical orders;' he had become very" stale" and' run down. He was again tested- and found to p.ave a fitness of fifty-five per cent; but, as before, the chapgewas evidenced by a movement of the "' air" curve.only._'

It is to be observed from the re~ults that, whim an overload is being' dealt with, even'the fittest me~ derive some assil:!bLnce from breathing enriched air, whil~ the unfit benefit to a still greater extent.' An 'overload to a relatively unfit person breathing' ordinary' air may become a normal load when he breathes, say seventy per cent o~ygen.· 'A man getting' fatigued while supporting what was at first a normal load but which has -now becoIPe an overlo~d, no matter how fit he may be, is relieved by . breathing enriched air-an' effect whi,ch has been remarked. by other observers. Conversely, heavy work can be ac~omplished with less fatigue when respiring oxygenated air conJinuously from the commencement: .

The meth{)d of, measuring fitness described above involves the assumption that Tang-fitness indicates general physical' fitness. Such l1Ppears actually to be the case if an exception be allowe/d in the instance' ,of pers'ons inured to living at a high altitude; in those circuII;lstan'c~s the' required degree of adaptation is' not derived so much from physical exercise as from long-conti,nued exposure to low oxygen pressure, and' , the lungs may '1?e 1highly 'efficient without general bodily fitness being

. " -, a necessary consequence. .

Bearing on the Oxygen Secretion-Questioll.-Since an unfit man derives much benefit during niuscular exertion through, addition of oxygen to the inspired air, whil~ a fit man is very little' benefited, it seems clear

, that the lungs of_the fit man absor? oxygen more readily from norma,} alveolar air during exertion. rrhis might be due elther to some anatomical change which makes simple diffusion occur more readily ,through the lung epithe,lium of the' fit man, or to activ~ seQretion of oxygen inwards by the lung ,epithelium. _ '

, The former theory does not_ seem ihherently probable; but if it were correct ~ie might expect' that even during rest the alveolai' .009

. percentage would be higher among fitthail amo.ng unfit men. 'l'~ ascertain whetherthi~ is so therecords,of eighty-Jour men were examined: They were of every-medical category, though the" A" class predominated. Their ages ranged fron;J. '15 to 50; though most were of the u,sual militaty age. ,T,he following table sets forth the expired 002 percentage sitting at, rest against ,the fitness factor, the latter having been determined as described aboye. -

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The evidence 1S -emphatically uegative; . the expired-C02-percel1tage

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at rest, and therefore, by inference. the oxygen tension of the alveolar air at rest, is not' affected by a very large variation in fitness.

Fitness per cent

40-50 50-60 60-70 70-80 80.-90 90-100

TABLE I. NUlfIber of

subjects examined

6 10 23 19 20 6

;.

-Average expired·CO~-per cent

. at rest 3'52 3'75 3'66 3'61 3'52 3-60

The secretion theory as propounded ~by Bohr and by Haldane and his co-wo~kers affords a more probable explan~tion., The: theory predicates that the epithelial cells possess the power, which they exercise in responsE1 to stimuli' originating in anoxremia of the tissues, 'of secreting oxygeilfrom the alveolar air into the blood [7]. When a' person is at rest he gets oxygen by simple diffusion; but during-work, or during existence at a high altitude, the amount so obtained is inadequate and is supplemented, as shown by tl:w experImental data of these observers, by ~ecretion. Once these cells are regarded, so -to speak, as oxygen pumps which can be set going when required, the experimental results' described above become' intelligible. Practice or training facilitates the oxygenation. of the blood by improving the cells' power of secretion. In. the fittest men, no benefit is derived during normal' load from breathing enriched air, since they, are

. able to get from normal air by secretion all the oxygen they need. The existence, in the lung epithelium, of a capacity which can be develope-d and intensified by training 'or other means of adaptation and . which inferentially may be impaired by overwork or overstrain, throws a new light on the phenomena of respiratory fatigue. .

pxygen Consumption.-'l'able, Il, which has been draw~ up from the, smoothed curves, gives, in litres per mmute of dry_. gas at N.p.r., the oxygen consumption of the, selected subjects whU~ 'doing work on the ergometer and while breathing both normal air and oxygen.

. - Efficiency 'of Ergometer Work.-The curves relating to effic,iency at different loads have a certain interest, though of all the results -these are perhaps most open to criticism and require most qualification. They were computed from the oxygen consumptions I!>nd.fr~m Zuntz's table of energyequivalents [8]. They are "gross" or. "overall" efficiencies and give, at different loads, the relation between the useful external work done by the human machine and the energy_ generated within that machine by exot.hermic chemical changes. A person' pedalling' the ergometer with the belt-off and thus doing no external work has, on this basis, zero efficiency. The accuracy of these estimates depends on several factors. The manner of arriving at Zuntz's figures has, the writer believes, been: considerably. criticized, though in view oC'the other' sources' of error now to be~ noted small imperfections in those V!1lues, are barely worth considering. - The

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evaluation of efficiency on normal load IS comparatively straigh~forwar,d and p'robably fairly'exact, but grave difficulties arise wben overloads are beingdeal,t with, . Being determin'ed from tbe oxygen consumption, an

. efficiency is evidently affected by errqr in measuring, the oxygen consumeq.,· Further, it is important to realize that, as a statement of the ~ate of oxygen consumption at a given time, say two 'minutes after starting an overload; a certain value may be accurate and yet it may yield altogether misleading results if used as the basis for calculating efficiency at the same time, This conclusion follows from the fact that to measure efficiency accurately there -

- must be a, correct correlation of energy-intake ~:iJ.d energy-output, There is, however, no such agreement'during an overload when' the output of energy, is, for a time, excessive, The portions of ' the curves which are considered unreliable for this rila~on are shown by even dots, , . \

TABLE II,-OXYGEN CONSUMPTION". ERGOMETER EXPERIMEN;S"

Work done in' foot-pounds per minute

Subject Sitting_at rest , 3,000 6,000 9,000 -

-Breathing Breathing . Breathing Bre~hing Breatlling Breathing Breathing Breathing

air - O:r air , .air 0, aIr O. -

I

---- ---------------------------I 0'28 0-31 '1'23 1:05 1'77 1'55 2'42 2'15

II 0'23 0'31 1'23 1'20 2'08 1'82 .2'42 2'30 ,Ill 0-37 0'22 , 1'03 0'81 2'62 1'30 2'20 2'10

IV 0'33 0'28 1 ;12 0'95 1'68 1'61 2'04 2'30 V 0'28 0'37 1'1'1 0'81 1'80· 1'44 - \ -

0'47 0'40' -1'17 1'02 'VI - - - -VII 0'45 0'40 1'13 1'05 1:70 ,1'49 .2'37 1'90

VIII 0'42 0'32 1'05 '0-97 1'58 1'50 2'27 2:60, IX 0-40 0'30 ,i'oO 1'05 1'68 1'62 2'30 2'30 X 0'37 0'28 1'12 0'81 1-83 1'28 2'52 1'70'

XII 0'40 0'41 .. 1'07 0'92 1'58 1'54 2'09 2-02 XIII (a) 0'33)

0'45 0'70)

1'05 1'17}_ 1'54 1'75 } 2'20 (b) 0'37 ) ' , l'30t, 2'00 2'65

XIV 0'38 0'25 1'17 0'92 2-09 1-65 2'62 ' 2'52 . XV 0'25 0'35 1'07 0'98 1'63 1'50 2'130

, - 2'30 XVIII 0'42 0'24 1'30 1'00 I 2'00 1'67 ,2'71 2'31

----,-' -------------------.. Average 0'36 0'32 1-12 0'97 1'74 - 1'54 2'33 2-16

If efficiency 'had been the subject under study, it would have be~n. necessary to endeavour ·to cor:r:ect the curves by taking into account the excess- ox¥gen consumption during the post-work period. An interesting feature (which has been noted by previous workers) becomes apparent

. -when an efficiency curve is corrected in that manner; it is, then seen to be dome~sbaped: in other words, as the load in.creasesthe efficiency reaches a maximum and then falls away again. The maximum occurs at or near, the line of demarcation of normal load and overload. Even with the uncorrected efficiencies graphed.,' the. tendency ~owards' the domed' form

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Hen.ry Briggs 291

. can be detected in several cases, as for 'example in that of Subject IX. , Zuiltz's values being based upon the respiratory quotient,' the abnormality of the respiratory quotient dudn,g severe work is another disturbing factor.

Generally speaking, the efficiency appears to be ,greater when breathing oxygen than when breathing ai~, 'With the relatively unfit person that

, ,effect may 'be partly due to the fact that, for a given load, less energy is consrim~d in respiration when. breathing oxyg~n. '

The efficiency of the flt is greater than that of the unfit man. This again may to some extent be owing to the relatively smail respiratory effort of the fit person: but no doubt the fact of the fit man being usually habituated to physical exertion, and having learnt to deal with a task with a minimuin waste of lllUscular energy as possible; has a great deal to do with his higher efficiency. For example, the expenditure of energy and consumption of . oxygen involved when ,a miner, use~ a shovel are markedly less than when the same task is performed'by a person unaccus-tomed to shovelling. '

CLIMBING 4,ND WALKING ,EXPERIMENTS.

A number of experiments were made on men climbing the main incline of the Burdiehouse limestone mine" Midlothian, both while breathing normal air 'and while bre~thing ,o'xygen. Preliminary t~~ts in' the Lingerwood andNewb~ttle collieries had shown the advisability of limiting the .variables. This could be done either by taking one subject on a number of gradients or 'by taking several subjects on one gradient, ang the latter alternative was chosen 'as being likely' to give most information. 'TheBurdiehouse incline lies at a uniform slope of 21 a.The roof is high, so that there, was no occasion to stoop, and the floor; ~hile dry for the m.ost part, was, at' the time of the tests,' wet and. slippery in places. On the whole the condition of' the incline ~jght be taken as a fair average of that of a mine roadway of heavy grade. Owing to'the difficulties encountered in fitting up, each day, a temporary laboratory on the side of the roadway, I had to be satisfied with a fewdeterminations for' each man; usually values were obtained at five rates of speed, both whenbreathing,air and when breathing oxygen.

It was intended to put the results, especially as to oxygen consutnption, in the most useful form for ~esigners and users of mine rescue apparatus; ther,efore the subject carried such an apparatus both d'iIring the climbing tests' ahd during the walking and running trials on the flat which are referred to below. The 'total weight borne on each occasion was about forty-three pounds. The values thus apply to fully equipped infantrymen. The procedure during these experiments was the following:

Breathing Normal Air.-T.pe subject carried a Douglas bagon his back ,and an exhalation 'bag,~ fitted with a relief valve, on his chest~ . He breathed through a mouthpiece, his nose' being clipped. Inhalation and

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exhalat!on valve~ were so placed that he drew air from, the Douglas. bag· and expired into the exhalation bag .. Before sta:l"ting, the Douglasbag was inflated. with a mea.sured volume:, of air by aid of a largedouhleacting bellows. The man was then -set. to walk up the incline (which was. marked.off in chains and poles) at the desired !-,ate; The three-way tap of the Douglas bag being "off," he inspired, at first, from the' atmosphere. When it was judged that his respiration had adjusted itself to the degree of exertion, the three-way-tap was turned" on" and he began to breathe, '0

from the measured'vohime in the Douglas bag. The length of the spell of work, from the moment of turning on the tap to the moment of turning it off again, was takeriby a stop-watch. After the spell samples for, analysis were'withdrawn, over mercury, from the exhala'tion bag, and the volume remaining in the Douglas bag' was metered. '

J3reathing Oxygen.~Before any observations were made on oxygen, the man was required: to use the mine rescue apparatus which he was carrying for a sufficient time to remove the bulk of the free nitrogeIi dissolved in the blood and tis~ues. During this preliminary' period'- the nitrogen percentage in the air' of the closed~circuit of the apparatus was' kept low by frequently' washing out through the relief valve with, excess oxygen. After that operation the subject. was not allowed to breathe ordinary air until the whole of the' oxygen 'series of tests was completed. During rests, and during the first parts of a cl~mb, while the respiration was accelerating, he used the rescue apparatus. The routine was the same as that described above, the Douglas bag, however, being' filled with' a measured volume of. oxygen, and the subject, on 'the wovd oJ command, changing rapidly from the rescue apparatus mouthpiece to that of the respiration apparatus, or vice versa. ,

The walking and running tests were made on a smooth, level concrete track at the mine rescue station, Edinburgh. .

. The results of two such tests are set forth in figs'. 12 and 13. Fig. 14 i's constructed from information relating to "C. G.D." and obtained from a paper ~y Haldane and Douglas [9J; it is included for the sake of comparison. In condition Ca), indicated on the graph by· full lines, this. subject was breathing ,normal air and, walking ;on the laboratory fioot, while in condition (b), indicated by chain dots, he was breathing air and walking in a level grass field.· He did not carry a load; therefore, the consumption of oxygen and production of carbon dioxide are relatively less than those of the other SUbjects. Though the figures actually obtained in Haldane and Douglas' experiments were used in drawing the graphs, twenty-five per. cent h,as been added to" C. G. D.:s" oxygen consumptions in the following table to make them more comparable with those of the other men, who were carrying forty-three pounds each. . .

Tables IIl, IV and V, derived from the smooth curves, . state oxygen consumptions(expressed, ~n litres per minute of ,dry gas at N.T.P.) of, men walking and Tunnipg on the flat and climbing the Burdiehouse incline: '




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TABLR HI.-OXYGEN CONSUMPTION. WALKING AND RUNNING ON THE' FLAT CARRYING wEiGHT

OF 43 LB.

, Sllbject

I II

In XIiI.-XVI

Average

\

Miles per hour ,--,---' -' -----, ------' --"------'--------,-----,

Standing ; 1 2- '8 4: 5

Br: ~ ~ ~ ~,

Br, Br. Br. Br. Br,' Br, Br. Br, Br, Br, Br, air 0, air 0, air 0, air .0, air 0, air 0.

0'71" 0'68" 0'77 0'91 0'85 1'14 0'95 1'40 2"12, 2'22 3'00 2'80 0'47 0'53 0'59 0'59 0'80 0'74 1'15 1'06 1'68 ' 1'59 2'20 ,2'10 0'25 0'41 0'64 0'47 0'90 0'70 1·17 0,'96 1'62 ,1'78 2'30 2'80 O'3t 0'28 0'60 0'63 0'88 1'00 1'20 1'38 1'60 1'75 2'90 2'70 0'55 0'57 0'70 O'S4 0'92 1,22 1'31 1'65 2'09 2'11 3'40 270

--0'40 '0'45 0:65 0'69 O'S7 0'96, 1'16 1'29 'l'S2 l'S9 2'80 2'60

C.G.D.(a) 0'40 ' O'60t 0'67+

1'47 '1'99

2'65 3·17 , (b) 0'40

" Unusu~lly high: omitted' in' averaging, t Interpolated from the graph. '

TABLE IV,-OXYGEN, CONSUMPTION, ~CLiMBiNG MINE INCLlNE or 21'\ CARRYIN(l.,48 LB,

Work done'in foot,ponnds per minute " ,--____________ , A ____ ~ ___ ,------------,

,Standing, 3,000 6,000' ' 9,000 .. --'--- ,-"-----..,---J--. .---'"-,

Subjec~ Breathiug 'Breathing Breathing Breathing Breathing Breathing Breathing Breathing air oxygen air oxygen air oxygen air oxygen

I II

'Ill XIII XVI

Average

0'62 0'57 i 'OS, 1·37 2'02 2'17 3'10 3'00 0'42 0'40 1'14' 1·19 2'20 2'55 3'40 0'35 0'41 1'14 1'09 2'19 2'05 0·47 0'45 1'40 1·24 2'56 2'37 0'45 0'47 1'24 1'24 2'02 2'02

0'46 0'46 1'20 2'21

3'10 2'80

3'00

2'60 2'85

3·00

TABLE V.-OXYGEN CONSUMPTION, CLIMBING MINE INCLINE OF '21°, CARRYING 43 LB,

Speed in mH,flB per hour; slope measurement

Subject

I II

HI XIII XVI

A.ve~age

,-----'-------------"----,--' ,-' --'------' --. Standing 0 '5 1'0, ,', 1 '5

..----'--~ ~ ;:--:-... Breathing Breathing Breathing Breathing Breathing Breathing Breathing

air oxygen air oxygen air oxygf'n air

0'62 0'57 1'10 1'40 2'lS2'25 0'42'0'40 1'10 ' 1'14 2'15 2'50 0'3,5 0'41 125 1'19 2'45 2'30 0'47 0'45' 1'50 1·31 ' 2'70 2 '46 0'45 ' 0'47 1'26 , +:26 2:04 2'04

0'46 1'24 1·26 , 2'30' 2'31

,

3'20

3'20 2'SO

Breathing oxygen' 3'10 3'40

3·CO

Most economical rate of walking.-;-Like a steamboat or an airship,' a man has a most economical :speed at which he goes farthest per litre of oxyg~n or pe; pound of fuel or' food consumed. Tbe data obtained yjelded the' following information: "C, G, D.'s"~ mO'st economical speed wllile breathing air and walking without burden on the laboratory floor, was four miles per hour, at which rate he moved ninety-nine yards per litre,

- of 'O~ygen --consumed. Walking without burden'on grass,' tbe same subject's most economical speed was_ three '~iles pet hour, when a litre carried him eigbtyo'two,yardEJ. With all the other subjects of Table III-




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294 'Physical Exertion, 'Fit1wss 'and Breathing

loaded"as each of them was, with forty-three pounds-the most economical speed proved to be three miles per hour when breathing air, while', when breathing oxygen and similarly loaded, that rate was th,ree miles per hour

',for I, II and Ill, and four miles per hour for ,XIII, and XVI.' It is , apparent- that increased,difficultyof waikirig,whether,a:~e to the mall carrying a weight or to lack of smoothness of the path, reduces the most e~onomical speed. ' ,

The writer, expresses his oblig{1tion and gratitude to Dr. J. S; Haldane for the encouraging interest he took in these experiments and for his equally invigorating criticism. Mention must -also be made of the, loyal assistance given by Miss Eliiabeth Gilchrist, M.A .. , B.Sc., 'and Mr. David Penman, B.S6., in conducting the experiments;, of the painstaking work of the Physical Test Station staff. and of, the very willing help given by a great many mine officials, miners, soldiers, and othersin the course of tests which were often of an arduous nature.

SUMM:ARY. '

(1) Physical work is found by experience to be easier to unfit men _ when' oxygenated air is breathed than, when normal air is breathed, but

no such difference is to be observed with fit men. , (2) When ,exertion' of steadily increasing magnitude is undertaken,

the expired-C02-percentage first rises and then falls. The load at 'which that percentage is 3. maximum is called the It crest 10ad."It is shown that the crest load demarcates between normal loads and' overloads. The demarcation, ,line is not const~nt, and the ~ircumstances 'causing movement of that line are ,discussed.

(3) If curves be drawn showing work done (abscissffi) and ,\exb!j.led~ CO2-percentage (ordinates), \ (a) when the subject breathes air, and (b), when he breathes oxygen,th~' curves are found to coincide,' up to the crest'where.the man is very fit and to diverge widely when he is u~fit, since the CO2-percentage becomes much lower in the unfit· when only ord,inary air is breathed. A method' of measuring fitness is described; it is' based.upon the experimental fact that"fitness is inversely as 'the divergence of these curves.

(4) On an overload, even the fittest man derives benefit from breathing enriched air. ' ~

(5) The nature 'bf the adaptation produced by physical,training and by certain vocations i~ compared with: that found to' result from living at a high, aJtitude. The bearing of' the results upon the, oxygen Recretion ' question is considered and reasons are givenfo'r the acceptance of the

~ secretion hypothesis. . ,. (6) The benefit of b:r;eathing enriched air when doing physical work

is limited to air containing about 60 per cent ,oxygen. Enrichment ,above that' proportion has. no effect a~ringexertion, even on very unfit persons. I

. (7) 'rabIes are inserted setting ,forth the oxygen consumptions of

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Henry Brl,ggs 295 ,

numerous 'subjects while' working the 'ergometer, while walking and running on the fiat, and while climbing a mine incline of 21° slope, and the most economical rates of walking are show~ for several sUbjects. . , .

, ApPENDIX. DESCRIPTION OF SUBJECTS SELECTED FOR ILLUSTRA'rION.

S~bject' I (fig. 3).-Miner .(repairer) working in steep seams, weight, 154 pounds, fitness eighty-three per cent; the position of the" peak load " (7,,500 to 8,000 feet pounds per 'minute) is higher than the average, indi-cating a man of good stamina. " .

'Subject II (fig. -4).-Sedentary person; weight, 136 'pounds; fitne!,s forty-six' per cent; finds work much easier when breathing oxygen; oxygen-~ant apparent at relati",ely low rates of exertion. '

Subject III· (fig. 5).-Instructor at a mine rescue station; weight, 165 pounds;, fitness eighty per cent.. .

Subject IV (fig. 6).-Mine undermanager; weight, 168 pounds; engaged' in a mine working flat seams; fitness, sixty-four percent.; oxygen·want becomes serious under 6,000 foot-pounds per minute. .

Subject VI (fig. 7).-Arm'y 'recruit; previously a bank clerk; weight, 142 pounds; fitness, forty-two per ·cent. _ - .

Subject VIII (fig. 8).-Regular soldier; weight, 168 pounds; instructor in physical drill; heavy weight lifter; athletic type; fitness, 100 per cent. Judging from his general behaviour while ·doing work,.(quite apart from tl;te results obtained) he is the fittest man of the series. Breathing oxygen is not the least benefit untit the crest load IS exceeded; then it gives a gradually increasing assistance. '. ,

Subject IX (fig. 9).-Minefireman or deputy, working i,n a {lat~seam coIlim;y; weight, 168 P9unds ;, fitness, sixty-nipe per cent. . .

Subject XIII (fig. 10).-First-class. footballer; runner, jumper an_d , all-round athlete; army instructor in physical drill; weight, 158 pounds.'

Records were, obFained of 'the subject in three conditions: (1) In g?od health; fitness, seventy'per cent (the ergometer results labelled (A) were

. obtained on that occasion)'; (2) in goodbealth and after intensive training at Aldershot; fitness, 100 per cent; and (3) in poor bealth; fitness fiftyfive. per . cent. The ergometer tests marked (B) ,and the Climbing and walking tests were carried, out with the man in the. last condition. The low rate of breathing, smalllpng-veI?tilation, great depth of breathing and abnormally high C()2-p~rcentage level are remarkable features.

Subject XV (fig. ll).-Assistant instructor at a mine rescue sj;ation ; weight, 147 pounds; fitness, sixty-three per cent .

. Subject XVI (figs., 12, 13). - Research assistant, sedentary habit'); weight, 154 pounds .. . C. G. D., fig. 14.




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[1] MARTIN •. JOURNAL OF THE ROYAL ARMY MEDICAL CORPS, 48; Proc. Physiol. Soc., p. xv, 1914;;' . [2] DOUGLAS. JOURNAL OF THE ROYAL ARMY MEDICAL'CORPS, 42; Proc. Physiol. Soc., p. xvii, 1911. [3J HALDANE and PRIESTLEY.· JOURNAL OF THE ROYAL ARMY MEDICAL CORPS, 32, p. 225, 1905. [4] HALDANE. "Methods of Air Analysis," second edition, 1918. [5] First Report of Committee. on Mine Rescue Apparatus, p. 61, 1918. . [6] HALDANE, MEAKINS, and PRIESTLEY. JOURNAL OF THE ROYAL ARMY MEDICA,L CORPS, 52,

p. 433, 1919. [7] DOUGLAS and-HALDANE. JOURNAL OF THE ROYAL ARMY MEDICAL CORPS, 44, p. 305, 1912;,

DOUGLAS, HALDANE, HENDERBON, and SCHNEIDER, Phil. Trans., 203 (B), p. 185,1913. [8] Quoted by BENEDICT and CATHCAR'l'. .. Muscular Work," Carnegie Institute, Washington

p. 33, 1913. . [9] DOUGLAS and HALDANE. JOURNAL OF THE ROYAL ARMY' MEDICAL CORPS, 45, p. 235, 1912.

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278 - bmj military health · '278 physical exertion, fitness and breathing.l by henry briggs,...

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