elderly man, and how is it possible to be sure that any particular subject

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1 THE INFLUENCE OF GRADED EXERCISES ON THE OXYGEN CONSUMPTION, PULMONARY VENTILATION AND HEART RATE OF YOUNG AND ELDERLY MEN. BY J. V. G. A. DURNIN and V. MIKULICIC.' From the Institute of Physiology, University of Glasgow. (Received for publication 29th May 1956) IN many countries the increasing proportion of elderly people is an important social problem. However, although a vast amount is written on this subject from many viewpoints, the industrial, the psychological, the geriatric, there are few reports of physiological studies. We know very little about the physiology, as distinct from the pathology, of the elderly. The lack of physiological information limits the practical applicability of surveys of the employment of elderly persons in industry, such as those of Richardson [1953] and Le Gros Clark and Dunne [1955]. Our scanty physiological knowledge is partly due to the difficulty* of precisely defining the terms used. What constitutes a "healthy'" elderly man, and how is it possible to be sure that any particular subject is in fact healthy? How detailed a medical examination must we have of each subject? What is the proportion of such "healthy" elderly people in the population? Physiological work with the elderly is more complex and requires more organization than similar work with young people. It would be most useful to know to what extent a healthy man of, say, 60 can exert himself physically and with safety. This might seem a comparatively simple problem: however, the results of previous work on the effect of exercise on circulation and on respiration in men of different ages are far from consistent; some results show little or no difference between young and elderly, others show a marked influence of age. The most extensive series of experiments is that of Robinson [1938]. He made several different measurements of cardiac and pulmonary function in boys and in men, ranging in age from 6 to 91 years, during and after both moderate and maximal exercise. The moderate [sic] exercise consisted of walking at 3-5 m.p.h. on an 8-6 per cent gradient, involving an energy expenditure of about 10 kcal/min. This, indeed, is severe exercise, especially for elderly subjects, and is more strenuous than they would ever be likely to undertake in normal life. In spite of this, there seemed to be little difference accountable to age, in oxygen consumption, pulmonary ventilation or heart rate, at any W.H.O. Fellow, Department of Medicine, Zagreb, Yugoslavia. 442

2 Exercise and Age rate up to an age of just over 60 years. Molina and Giorgi [1951], on the other hand, found a variation between young and old during work of moderate and high intensities on the treadmill. Mahadeva, Passmore and Wolff [1953] measured the oxygen consumption of men and women, whose ages ranged from about 14 to 70, during a step test and while walking on the level. These experiments again seemed to indicate that age had no effect. Ryhming [1954], in a small series on a group of 8 men between 55 and 65 doing a step test, found a tendency for the heart rate both during the test and immediately thereafter to be sonmewhat higher than in a younger group. Hellon, Lind and Weiner [1956] studied young and middle-aged men working in a hot environment. They observed the pulse rate, the blood pressure and the body temperature after work. There was a significant difference between the age-groups under these circumstances. Because of such conflicting results, we decided to compare some effects of exercise on the respiration and circulation of a group of young and a group of elderly men. Since the nature of the exercise might influence the results, both groups carried out arm exercises and walked on a treadmill. An attempt was thus made to answer two distinct questions: firstly, was there a difference between young and elderly men caused by exercise in general? Secondly, did the amount of gross body movement during the exercise have a separate effect? METHODS Subjects.-Measurements were made on 24 men in all, 12 in each age-group. The young men were years and the elderly years. The ages, heights, weights and resting heart rates are given in Table I. Both groups were employed normally as general labolrers. TABLE I.-AGE, HEIGHT, WEIGHT AND RESTING HEART RATE OF THE 'SUBJECTS (Weight was taken in ordinary clothes but without sho-3 or janket) Elderly Young 443 Subject Age Ht. Wt. Pulse Subject Age Ht. Wt. Pulse (cm.) (kg.) (per min.) Sbe(cm-) (kg.) (per min.) D. A M. O'C J. C G. MCL A. L C. M C. S J. D R. W J. W D. S M. L J. R V. M F. S J. D J. P J. G J. P S. F A. F H. D J. MCC J. G

3 444 Durnin and Mikulicic Before they acted as subjects, a detailed clinical history was taken from each and they were all given a complete routine medical examination. All were apparently healthy. Exercise.-Four different grades of regulated exercise were done, two on an arm ergometer [Cathcart, Wishart and McCall, 1923] and two on a treadmlill. One of the arm exercises was light in nature, involving an average energy expenditure of just over 4 kcal/min. The first of the treadmill exercises, walking on the level at 3-7 m.p.h., and the second arm exercise were of similar degree and of moderate severity. The second treadmill exercise, walking on the level at 4-3 m.p.h., was slightly heavier. Plan of Experiment.-One elderly man and one young man were studied together. The statistical plan of the experiment was in the form of three 4 x 4 Latin squares, the variables being the subjects, the order in which the different exercises was done, and the four grades of physical work. This arrangement helped to eliminate any effect which might have been caused by environmental conditions and by the order in which the exercises were performed, whereby fatigue might have influenced some particular results. An analysis of variance on a splitplot basis was done on the various data. Before the experiments, each man was accustomed to walking on the treadmill normally at the different speeds. Only a few minutes of practice with the arm ergometer was required. The experiments were begun at least two hours after the previous meal which, in all cases, was a light one. During the period of the exercise, continuous readings were taken of pulmonary ventilation and heart rate and a sample of expired air was collected; immediately after the work, the subjects rested sitting while the blood pressure and the heart rate were recorded for the first 10 nmin. of recovery. Oxvgen consumption and energy expenditure were calculated for the "steady state "-i.e. 3-5 min. were allowed after beginning the exercise before a sample of expired air was taken for analysis. The energy expenditure was calculated by Weir's method [Weir, 1949]. Apparatus.-Pulmonary ventilation was measured by means of Max Planck respirometers [Miller and Franz, 19,52]. These instrumnents were calibrated frequently as described previously [Durnin, 1955]. Expired air was analysed using the Haldane gas analysis apparatus. Continuous heart rates were recorded by a rather radical adaptation of the Miller Pulse Counter [Miuller and Reeh, 1950]. RESULTS The statistical analysis of the Latin squares on a split-plot basis showed, initially, that there was a significant difference between columns but not between rows. The significance of the column mean square indicated that the differences from one pair of men (one old and one young) to another pair are greater than the differences within each pair

4 for the same exercise. Exercise and Age The lack of significance in the rows showed that the order in which the exercise was done had no appreciable effect on the results. That is, there was no carry-over effect from one exercise to a subsequent one. As would be expected, there was a very highly significant difference caused by the different exercises. Subsequent analysis of the sub-units gave a highly significant variation of the two age-groups related to the exercises in general. Accordingly, each exercise was tested separately to find whether there was a significant difference between old and young. Oxygen Consumption and Energy Expenditure.-The mean oxygen consumption, energy expenditure and respiratory quotient for the 12 elderly men and the 12 young men are given in Table II. The mean TABLE II.-MEAN VALUES FOR OXYGEN CONSUMPTION, ENERGY EXPENDITURE AND RESPIRATORY QUOTIENT FOR ELDERLY AND YOUNG SUBJECTS DURING THE FOUR GRADES OF EXERCISE. Oxygen Energy consumption expenditure R.Q. Exercise (1./min.) (keal/min.) Arm ergometer 1 Arm ergometer 2 Treadmill 1 Treadmill values of the oxygen consumption and the energy output of the elderly men were higher than those of the young men. The differences between the two groups, however, while doing each of the arm ergometer exercises were not statistically significant. On the other hand, in each of the two treadmill exercises, the differences between the elderly and the young were highly significant (P < 0-01 for Treadmill 1 and P < for Treadmill 2). The respiratory quotients were somewhat higher in the elderly than in the young during walking on the treadmill. Pulmonary Ventilation, Oxygen Extraction and Ventilation Equivalent for Oxygen.-The values for these are shown in Table III. The TABLE III.-MEAN VALUES FOR PULMONARY VENTILATION, OXYGEN EXTRACTION AND VENTILATION EQUIVALENT FOR OXYGEN FOR ELDERLY AND YOUNG SUBJECTS DURING THE FOUR GRADES OF EXERCISE. Pulmonary Oxygen extraction (percentage ventilation (1./mm. at difference between inspired VEo2 BTPS) and expired air) Arm ergometer Arm ergometer Treadmill Treadmill VOL. XLI, NO I~~~~~~~~~~~~~~~

5 446 Durnin and Mikulicic pulmonary ventilation of the elderly was higher in all four degrees of work than that of the young men. However, again the difference in the two arm exercises was not significant, whereas the elderly gave significantlyvgreater values on the treadmill (P < for T1, P < for T2). The results for oxygen extraction-i.e. the difference in the percentages of oxygen in the inspired and in the expired air-show the opposite tendency, although once more this difference is only significant in the treadmill studies (P < for T1, P < for T2). The ventilation equivalent for oxygen, calculated as the total pulmonary ventilation in 1./min. (BTPS) x 0 1, divided by the total oxygen consumption in 1./min., also showed similar differences between old and young. (No significant variation in the arm exercises: P < 0.01 for Treadmill 1, P < for Treadmill 2.) Both the oxygen extraction and the ventilatory efficiency increased steadily in all cases as the degree of heaviness of the work increased, but the extent of this was more marked in the walking than in the arm exercises. This is probably due mainly to the relatively fixed position of the thorax during the arm exercises which would diminish respiratory efficiency. However, even with the heaviest exercise, the VEo2 of the elderly men show that the respiratory efficiency was still quite high. Heart Rates.-Figs. 1 and 2 give the mean heart rates of the elderly and young men for each of the four grades of exercise, and Table IV shows the statistical significance of the differences between the two groups of men. In order to find at which point any difference between elderly and young might arise, either during the exercise or in the period of recovery, the heart rates were compared at four separate intervals in each form of exercise. It was thought that differences might be more likely to occur either during the period of adaptation to exercise, or immediately following this period. Accordingly, the heart rates during the first 3 min. were analysed, both for young and old, and compared. The subsequent 5 min. were next analysed; if the heart rates of the elderly men increased steadily at a greater pace than the young men, then a statistical comparison of this second period should have shown a significant difference. During recovery from the exercise, the immediate fall in pulse rate during the first 2 min. is an obvious period where possible differences might become apparent, so a statistical analysis was done here for young and old. The 3rd to the 10th min. of recovery were next analysed to determine whether the elderly might show a more gradual return to normal rates than the young. Although resting heart rates were obtained, it was decided to use the gross rate for the statistical analysis. Table IV shows that, in similar manner to the other measurements, there is no significant difference with the arm ergometer exercises between elderly and young in any of the four different periods analysed. (The difference between the pulse rates of the elderly and of the young

6 _- ARM ERGOMETER *--*OLD A-A YOUNNG :~~. ARM OLD ERGOMETER A... YOUNG ii00 ui LU 90 ui I sc I, 0, // ZI I -all EXERCISE Time in minutes RECOVERY I I I FIG. 1.-Mean heart rates of the group of elderly and of the group of young men during the arm exercises and for the first 10 min. after exercise. _-@ OLD TREADMILL I A-A YOUNG O"*^0 OLD TREADMILL 2 A...A YOUNG cc,i Time in minutes FIG. 2.-Mean heart rates of the group of elderly and of the group of young men during the walking exercises and for the first 10 min. after exercise.

7 448 Durnin and Mikulicic TABLE IV.-RESULTS OF THE STATISTIcAL TREATMENT OF THE DIFFERENCES IN THE HEART RATES OF THE ELDERLY AND YOUNG MEN DURING AND AFTER THE FOUR GRADES OF EXERCISE. (NS =not significant; * = significant) During exercise During recovery Exercise,, Min. 1-3 Min. 4-8 Min. 1-2 Min Arm ergometer 1. NS NS NS NS Arm ergometer 2. NS NS NS NS Treadmill 1.. (P < 0.05)* NS NS NS Treadmill 2.. (P < 0 05)* NS NS (P < 0-05)* men during recovery is considerable, but is not statistically significant. The possible reasons for this are discussed later.) However, with the treadmill there is a difference for the first 3 min. of exercise (P < 0 05 for T1 and T2) and also for the 3rd to the 10th min. of recovery in the second degree on the treadmill (P < 0.05). The initial increase of pulse rate of the elderly in the first treadmill exercise means that this increase is reflected also in the rates during recovery. Thus, after exercise, although the rates differ markedly from each other, the slopes of the lines do not vary significantly. In the second treadmill exercise, along with the divergence caused by the more marked increase by the old in the first 3 min. of exercise, there is as well a difference in the degree of slowing of the heart rates of the elderly and young men during the 3rd to the 10th min. after work. Blood Pressure.-The systolic and diastolic arterial pressures were measured immediately on cessation of the exercise and thereafter at minute intervals, until they had returned to a fairly constant level. In Table V, the systolic and diastolic blood pressures are shown for the TABLE V.-MEAN VALUES FOR BLOOD PRESSURE AFTER EXERCISE Exercise 1st min. 5th min. Ie Arm ergometer /85 120/75 125/85 115/80 Arm ergometer /85 125/85 130/90 110/75 Treadmill /80 120/75 120/90 110/75 Treadmill /85 130/75 130/85 110/75 1st and for the 5th min. after exercise. These times were deliberately chosen in the hope that the results in the first minute after cessation of the exercise would reflect the influence of the exercise; results five minutes after cessation of the exercise ought to reveal differences in rates of recovery. There was not a large difference between the age-groups, except in the initial levels of the systolic blood pressures, which were somewhat higher in the old-as might be expected.

8 Exercise and Age 449 DiscusSION The treadmill studies showed quite a clear falling-off in circulatory and pulmonary function in the elderly men; the degree of this deterioration became more marked as the severity of the work increased. The extent of this diminution in function, however, is much less than that of the increased work done. In other words, the percentage decrease of oxygen extraction and ventilatory efficiency are not nearly so marked as the percentage increase of pulmonary ventilation and oxygen consumption. Had the oxygen consumption of the elderly been the same as that of the young for the same work, the increased pulmonary ventilation would have indicated of necessity a decreased oxygen extraction and, therefore, a lower ventilatory efficiency. In fact, even with this lower respiratory efficiency the total oxygen consumption for equal work was markedly greater in the elderly. How the oxygen useage for an identical physical task should be increased in the elderly is perhaps not obvious, on a priori grounds, and will be discussed later. The exact implications of the effects on heart rate are more difficult to assess. There has never been unanimity of opinion among physiologists about the usefulness of the heart rate as an index of physical fitness or as a measure of the physical load of exercise on the body. There are four ways by which pulse rates may be used to indicate physical strain on the body. In many exercise tests the rate of recovery of the pulse, during the first few minutes after work, is used as a measure of fitness. In others, the increase in the pulse rate during work is compared to the resting level. Yet again, the correlation between the pulse rates during and after work provides an index of the severity of the work. A fourth index utilizes the total pulse count during the exercise and the pulse recovery sum, both values being expressed as net figures, the resting pulse rate being deducted. However, in spite of all the data which has been accumulated on pulse rates at rest, and during and after exercise, it is still not possible to say with certainty what is the exact relationship in an individual between these variables; some apparently well-controlled experiments appear to show little relationship between resting pulse and the recovery time, resting pulse and the increase of exercise (e.g. Elbel and Holmer, 1949], and the pulse rates during and immediately after exercise [Elbel and Holmer, 1949; Ryhming, 1954]. Since we were only interested in comparing the results of one group to those of another, the exact method of using the pulse rates was not of major importance, as long as this method remained identical for each group. The comparison of regression lines of gross heart rates, during the four periods described for each exercise, allowed the direct effect of the exercise to be studied. The initial resting pulse rate and the actual values recorded during and after exercise were thus less important

9 450 Durnin and Mikulicic than the rapidity with which the heart rates increased during work and fell after work, and the way in which the new levels gradually changed; this change might have been due in the one case to fatigue or in the other to a slower recuperative process. In both arm ergometer exercises, the speed at which the heart rates of both elderly and young subjects adapted to exercise was much the same. Both arm exercises showed, however, that the decreased pulse rate reached 2 or 3 min. after exercise stopped was a little higher in the elderly than in the young, although the variance within the age-groups was greater than the variance between the groups: consequently, this difference was not significant at the 5 per cent level. For instance, the coefficient of variation for the second arm ergometer exercise during recovery was 12 per cent for the old and 14 per cent for the young men. Thus, although the heart rates after exercise appear quite different, it is not possible to say from the results whether the difference is a true one. With the treadmill exercises, the load on the circulation of the elderly subjects was obviously greater than on the young, and the initial pulse rise in the first 3 min. was higher. Thereafter, rates did not differ significantly in their further increase, although, had the exercise continued for a sufficiently long period, it is likely that a difference would have appeared with the faster degree of walking. During recovery after walking at 3.7 m.p.h., the heart rates of the elderly were again higher than those of the young men, although for the reasons already given the difference was not significant. The recovery from the 3rd to the 10th min., however, after walking at 4.3 m.p.h., demonstrated significantly slower circulatory recuperation in the elderly. The present experiments indicate that there is a difference between elderly and young in the energy cost of moderate exercise on the treadmill. Two possible factors may contribute to this difference. First, although a careful routine medical examination was made of all the subjects, there may have been minor arthritic, arterial, cardiac or pulmonary damage in the elderly. All these may have influenced our results and may have contributed partly to the varied results obtained by other authors. Elderly subjects for experiments on physical working capacity should certainly have a much stricter medical examination beforehand, including an ECG, and X-ray examination of joints and chest. This, of course, complicates the selection of subjects, but would seem to be the only way to ensure the study of a healthy group of old persons. On the other hand, such a healthy group may not be representative of elderly persons in general. A second factor in the present investigation which might have affected the increased metabolic cost of the treadmill exercises in the elderly was the heavier mean weight of this group. The mean body weight of the young men was 64 kg. and that of the old 68 kg. However, this increase was caused very largely by one excessively heavy man,

10 Exercise and Age 451 and the average of the remaining eleven elderly men was very little more than that of the young (see Table I). In any case, even for the full group of elderly men, if the energy expenditure is calculated on a "per kg. of weight" basis, the statistical significance of the results remains exactly as before. Whereas the second arm exercise and the first treadmill exercise made an almost similar demand for energy expenditure on the young, for the elderly the walking demanded a much greater expenditure of energy than did the arm exercise. The severity of the physical task was apparently not the sole determining factor. At present the reasons for this are speculative, but they may be of some practical importance. Elderly people may be able to carry out quite efficiently movements of restricted muscle groups, such as the arm and shoulder muscles, even though these movements involve a considerable expenditure of energy. On the other hand, the more complicated activity of walking, which requires the use of large muscle masses, the movement of many joints and continuous readjustment of posture, may perhaps be less perfectly regulated in the elderly than in the young. SUMMARY 1. The effects of exercise were compared on two groups of healthy men, the one aged years and the other aged There were 12 men in each group. 2. Four grades of exercise were used, two on an arm ergometer and two on a treadmill. The first arm exercise was light in nature, involving an average energy expenditure of just over 4 kcal/min. The second arm exercise and the first treadmill exercise, walking on the level at 3.7 m.p.h., were of moderate severity. The second degree on the treadmill, walking on the level at 4-3 m.p.h., was more strenuous. 3. Oxygen consumption, pulmonary ventilation and heart rates were recorded during the exercises, and the heart rate and blood pressure were followed during the first 10 min. after the work. 4. There was no significant difference in these measurements, nor in oxygen extraction or ventilation equivalent for oxygen between the groups with both arm exercises. However, the lighter exercise on the treadmill, which for the young men made a similar metabolic demand to the second arm exercise, gave significantly different values for the elderly. The older men used more energy, had a lower respiratory efficiency and higher pulse rates for the walking than the young men. The heavier treadmill exercise further increased these differences between young and old. The elderly men thus seemed to be able to do even quite hard exercise very efficiently if they were stationary, whereas the movements of walking caused a marked lowering in their efficiency. 5. The detailed results are discussed and compared with some finding of other authors.

11 452 Durnin and Mikulicic ACKNOWLEDGMENTS We are indebted to Dr. R. A. Robb and to Dr. S. D. Silvey, of the Department of Statistics of Glasgow University, for assistance with the planning of this experiment and with the statistical calculations. We are also grateful to Professor R. C. Garry for advice, and to Mr. Harris of the Electronics Division of the Natural Philosophy Department for help with the electronic pulse counter. The expenses were borne very largely by a grant from the Medical Research Council. REFERENCES CATHCART, E. P., WISHART, G. M. and MCCALL, J. (1923). "An ergometer adaptable for either hand- or foot-movements", J. Physiol. 58, CLARK, F. LE G. and DUNNE, AGNES C. (1955). Ageing in Industry. London: Nuffield Foundation. DURNIN, J. V. G. A. (1955). "The oxvgen consumption, energy expenditure and efficiency of climbing with loads at low altitudes", J. Physiol. 128, ELBEL, E. R. and HOLMER, R. M. (1949). "The relationship between pre-exercise pulse rate and recovery following exercise", Res. quart. 20, HELLON, R. F., LIND, A. R. and WEINER, J. S. (1956). "The physiological reactions of men of two age-groups to a hot environment", J. Physiol. 133, MAHADEVA, K., PASSMORE, R. and WOOLF, B. (1953). "Individual variations in the metabolic cost of standardized exercises: the effects of food, age, sex and race", J. Physiol. 121, MOLINA, C. and GIORGI, E. (1951). "Il metabolismo respiratorio dei soggetti anziani durante l'esercizio muscolare", Med. lavoro. 42, MtLLER, E. A. and FRANZ, H. (1952). "Energieverbrauchsmessungen bei beruflicher Arbeit mit einer verbesserten Respirations-Gasuhr", Arbeitsphysiologie, 14, MtLLER, E. A. and REEH, J. J. (1950). "Die fortlaufende Registrierung der Pulsfrequenz bei beruflicher Arbeit", Arbeitsphysiologie, 14, RICHARDSON, I. M. (1953). " Age and work: a study of 489 men in heavy industrv", Brit. J. industr. Med. 10, ROBINSON, S. (1938). "Experimental studies of physical fitness in relation to age", Arbeitsphysiologie, 10, RYHMING, IRMA (1954). "A modified Harvard step test for the evaluation of physical fitness", Arbeitsphysiologie, 15, WEIR, J. B. DE V. (1949). "New methods for calculating metabolic rate, with special reference to protein metabolism", J. Physiol. 109, 1-9.