Muscular Activity

A short bout of exercise is taken, mild to moderately severe, and the total oxygen used and the total CO. given out, during the exercise and in complete recovery from it, are been given out, in the same time, reckoned at the rest-— ing rate before, or as the average of before and after, the experiment. The differences represent the oxygen and the CO, consumed, and produced, as the result of the exercise. Provided the bout of exercise be not too pro-

hydrate has been oxidized, and the body has returned, without any extra consumption of fat to its original condition. If the exercise be continued for a long time the respiratory quotient of the exercise plus recovery is low: if © it be of an intermediate duration the respiratory quotient also is intermediate: if it be very short the respiratory quotient is unity. An element of muscular exercise, therefore, is conducted simply at the expense of carbohydrate: © while if the exercise be prolonged other metabolic processes —

Among other things the speed of the recovery process depends on the rate at which oxygen can be supplied to the active muscles. This is limited by two factors: first, the total oxygen that can be taken through the lungs into Fig. 12. To SHow Tam SpeEp oF THE Recovery Process In MEN Breataine Gas Mrxtures Ricn (Experiments 1 To 4) anp Poor (EXPERIMENTS 6 AND 7) IN OXYGEN Note that these curves (especially experiments 3 to 7 on a single subject) do not show a more rapid recovery at higher oxygen pressures. Cf. figure 7. (Hill, Long and Lupton, 1924.)

the blood and circulated by the heart; second, the local circulation to the part involved. This factor of oxygen supply is not usually important in a healthy man after exercise is over: once the initial rapid drop in the oxygen intake has occurred the oxygen supply is apparently quite adequate to the needs of the muscles, the circulation rate — falls off, the arterial blood is fairly completely saturated, and no increase in the speed of the recovery process occurs if the subject breathes a gas mixture considerably enriched — with oxygen (fig. 12). In abnormal conditions of course, as in the isolated muscle, the factor of oxygen supply may be of great importance in determining the speed of the recovery process. In the broader sense, however, all oxidation in muscle is recovery oxidation, and during continued exercise the oxygen intake determines the speed of recovery from previous elements of the exercise. Many observations have been made of the oxygen intake of a man undergoing various forms of severe muscular

is 4.2 litres per minute; breathing 50 per cent oxygen, very — nearly 6 litres has been reached, and that by a subject who has never reached more than about 3.8 litres in air. The only possible reason why more oxygen can be taken in, when breathing oxygen, is that the blood is not completely saturated during very severe exercise when breathing air; the greater saturation, however, of the coronary blood, when breathing oxygen, may then result in greater cardiac activity. The magnitude of the oxygen intake is deter- — mined mainly by the capacity of the heart, and I will give later a calculation showing what this number means in heart output. The other factor determining the speed of the recovery process is the local supply of blood to the muscles actually involved. Lindhard showed that in such exercise as holding the body with arms bent, on rings in a gymnasium, the blood supply to the active muscles of — the arm is almost completely cut off. The whole of the oxygen required had to be used after the exertion was over. In running the supply of blood to the active muscles is particularly easy, as they are never rigid and their movements are rapid.

The values of the oxygen intake during severe exercise allow a striking—if approximate—calculation of the output of the heart. Assuming, as was the case in the subject who consumed 5.9 litres of oxygen per minute, an oxygen capacity of 21 cc. per 100 cc. of blood, and an average utilisation coefficient of 75 per cent (a value as high as has even been recorded), then the actual oxygen taken in must have required 37.5 litres of blood per minute to carry it. This amount of blood has been ejected from the heart twice, from the right side once and from the left side once; altogether, therefore, 75 litres of blood—about 17 gallons, about 120 times the heart’s own volume—have been pumped out in every minute. Even assuming a utilisation coefficient of 100 per cent, 56 litres (123 gallons) of blood must have been pumped together from the two sides of the heart. Compare these volumes with the amount of water which a bath tap can pour out in a minute, even when turned full on. In such exercise the heart-rate —recorded with a string galvanometer—is about 180, which means that each side of the heart ejects some 200 cc. per beat. There is no possible flaw in the argument or calculation, otherwise it would be difficult to believe the conclusion. It is little wonder that the heart sometimes cannot stand the strain.

It is possible, by an approximate calculation to determine the oxygen consumption of the heart during such exercise. The calculated output of blood, multiplied by the blood pressure, gives us the work done; assuming a mechanical efficiency of 20 per cent, which is a high value under such conditions, the total energy used by the heart can be calculated. The provision of this energy requires the consumption of oxygen, and it would appear that the

oxygen requirement of the heart ‘agene such exercise a8 that described above is about 300 cc. per minute—about half its own volume. Assuming a utilisation coefficient — of 75 per cent and an oxygen capacity as before, this requires two litres of blood to pass through ~ the coronary vessels of the heart per minute. This volume of oxygen, — actually used by the heart, is almost equal (per gram) ' to that required (but not obtained) by voluntary muscle during very violent exercise. The muscle has to stop — within a minute, owing to oxygen-want; the heart, how- — ever, owing to its better oxygen supply, when the coronary — circulation is efficient, is able to keep up an qutput of this — order for long periods. It would seem possible that a deciding factor in the capacity of a man for severe prolonged exercise may often be the efficiency of his coronary — circulation.

The recovery process depends also on other factors. In a previous lecture I showed how in the isolated muscle it — depends on the hydrogen ion concentration. Deep breathing, therefore, sweeping away the CO, and keeping the ~ body alkaline, may be advantageous to the quickness of — the recovery process. It must depend also upon the presence of oxidative catalysts, such as those recently — described by Hopkins, Meyerhof, Warburg, and others. It is likely that the oxidising faculty of tissues will vary — from individual to individual. It may be, therefore, that — important divergences from’ the normal will be found in persons suffering from various forms of dyspnoea, in respect of their oxidative metabolic power. Possibly athletes, and — people accustomed to heavy work, will develop this side of their metabolic activities. Recent work in Hopkins’ laboratory has shown that haemoglobin has a very distinct catalysing power in the oxidation of unsaturated fats. — The dyspnoea so often associated with anaemia may in —

some cases, be due to the absence not only of an adequate oxygen supply and of adequate blood and tissue buffers, but of an adequate amount of some oxidising catalyst. Recent work by Warburg and his colleagues has shown that many forms of biological oxidation probably occur as surface phenomena, catalysed by iron atoms embedded in the surface; the absence of the iron, or its removal from activity by physical or chemical means, will hinder or prevent oxidation, as also will displacement of the oxidisable bodies, by narcotics or other substances, from the active surfaces where oxidation goes on. Imperfect metabolism of iron, excretion of it, its combination with abnormal metabolites, the displacement of the bodies to be oxidised away from the oxidising surfaces might all lead, therefore, to an imperfect and slow recovery from exertion, to dyspnoea associated with exercise.

All of us can suffer from dyspnoea and all of us can exhaust ourselves very rapidly; the finest athlete in the world may be almost incapable of movement within 50 seconds from the beginning of a race. The same degree, however, of exhaustion may be produced by a much lower level of exercise, no more rapidly but just as effectively, in a person of lower oxidative faculty or with poorer buffers in his tissue. When I was lecturing recently in Holland on this subject it was remarked, after one of my lectures, that it was typical of an Englishman, when he had found an interesting bit of physiology, immediately to want to apply it to sport. Perhaps some of you will sympathise with the motive, even if the charge be true. There is a better one, however; athletes and healthy men give us the cleanest experiments. If one took a patient from the hospital and made him work till he could barely move, one could never be sure (a) that he had really driven himself to his limit—it requires an athlete to know how to

exhaust himself; (6) that one would not kill him; and (c) what the cause of his stopping was. With young athletic out,” moderately certain of not killing them, and practically certain that their stoppage is due to oxygen-want and to lactic acid in their muscles. Quantitatively the phenomena of exhaustion may be widely different, qualita-_ tively they are the same, in your athlete, in your normal man, in your dyspnoeic patient. You can only observe your patient, but you can experiment with your athlete; you can ‘‘try out” on him the facts and theories which you have reached with frogs. There I must leave it, and be grateful if the young athletes in their turn can suggest further experiments on frogs.

The work which I have described to you today is largely due to the devotion and enterprise of my friend and colleague Hartley Lupton. Lupton, alas, at the early age of not live to see the published account of his investigations, but I hope that they will remain associated with his name. He wrote me a fortnight before his death saying how he would have loved to be in this place, to hear me discuss — this work with you. Never did he admit that he would |

His work will survive him, and will result, I am happy to’ believe, some day in the alleviation of human suffering, — insofar as it leads to a better understanding of the processes of the living healthy body: it has its implication in medicine, — as well as in physiology: it will prove a sufficient monu-— our countries, to speak to you. I am very sensible of — that honour. I have many reasons indeed to be grateful . to you and to your countrymen. I have the happiest —

memories of friendship and codperation with Americans, in the laboratories at Cambridge, Manchester and London, and in other places and circumstances during the war. University College also, from which I come, owes much, very much, to the generosity of the Rockefeller Foundation. And to all this you have added the singular kindness with which you have received me, and the patience and forbearance with which you have heard me. Perhaps some of you may, some day, add to that kindness by coming to work with me in England.

A. V. Hint anp Lupton: Muscular Exercise, Lactic Acid, and the Supply and Utilisation of Oxygen. Quarterly J. of Medicine, 16, p. 135, 1923. Lone: Lactic Acid in the Blood of a Resting Man. J. Physiol., 58, p. 455, Furvusawa: Muscular Activity and Carbohydrate Metabolism in the Normal Individual. Proc. Roy. Soc., 98 B, p. 65, 1925. Krogu anv Linpuarp: Relative value of Fat and Carbohydrate as Sources of Muscular Energy. Biochem. J., 14, p. 290, 1920.

Barr anp Himwicu: Comparison of Arterial and Venous Blood Following Vigorous Exercise. J. Biol. Chem., 55, p. 525, 1923. Absorption (apparent) of heat, Accumulator, analogy to muscle, 42 Adam, N. K., 79 Adaptation of energy to work, 48 “All or none”’ principle, 48, 49 Analysis of myothermic records, Athlete, lactic acid formation in, 87 experiments on, 109 Athletic records, 98 Azuma, 47, 49, 50 Caffein, 45, 75 Calibration, 33 . Carbohydrate as fuel of muscle, ‘Carbon dioxide, 55, 56, 57, 68 in exercise and recovery (man), Chronaxie, 73 Circulation and oxygen, 66 Contraction, heat in, 63 Contracture and heat-production, Coronary blood flow and cardiac activity, 106, 108 Curare, 73 Cystein, autoxidation of, 68 Cyanide, 69

Damping of vibrations by excited _ muscle, 17 Delayed production of heat, 37, 38, Downing, magnet system, 40 Duration of stimulus and heat, 43 Dyspnoea, 109 “Efficiency” of maintaining contraction, 44 ‘Efficiency’? of recovery, 67, 88, Elastic body, muscle as, 3, 41 Electric charge on surfaces in muscle, 80, 81 motor, analogy, 48 theory of contraction, 80, 81 Electroplated thermopiles, 30 Embden, 58, 61 Energy in anaerobic contraction, Equivalent mass, 9

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