BETWEEN SUBJECTS DIFFERING IN BODY WEIGHT. By

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1 Q. Jl exp. Phy8iol. (1969) 54, HUMAN CARDIOPULMONARY RESPONSES TO EXERCISE: COMPARISONS BETWEEN PROGRESSIVE AND STEADY STATE EXERCISE, BETWEEN ARM AND LEG EXERCISE, AND BETWEEN SUBJECTS DIFFERING IN BODY WEIGHT. By J. E. COTES, D. ALLSOPP and F. SARDI*. From the Pneumoconiosis Research Unit of the Medical Research Council, Llandough Hospital Penarth, Glamorgan. (Received for publication 30th September 1968) The regressions of the oxygen uptake on rate of work, of the ventilation and cardiac frequency on oxygen uptake, and of the ventilation on tidal volume have been obtained over the ranges where they were linear during pedalling and during cranking a cycle ergometer. The regression coefficients for ventilation and cardiac frequency on oxygen uptake are higher for light than for heavy subjects, and for work which is performed with the arms instead of the legs; possible reasons are discussed. The respiratory frequency in relation to tidal volume is also higher for arm than for leg work. In the comparison of progressive and steady state exercise no systematic differences were observed, except for the relationship of the consumption of oxygen to the rate of work; this finding is relevant to the planning of exercise studies on normal subjects. PROGRESSIVE exercise has the advantage over steady state exercise of taking less time to span a range of energy expenditures; so it has been used for assessment of the maximum oxygen uptake [Nagle et al., 1965; Shephard, 1967; Allen et al., 1968]. It has also been used for assessing cardiovascular performance [Miller, 1950]. However, the oxygen uptakes in relation to the rate of work are lower and probably more variable than for steady state exercise. In the present study the validity of progressive exercise for obtaining the relationships of ventilation and cardiac frequency to the uptake of oxygen, and of the ventilation to the tidal volume, are considered for arm and leg exercise in light and heavy subjects. The results show the procedure to be of practical value; they also suggest that the size of the muscles has an important effect upon the physiological response to exercise, even when this is entirely aerobic. SUBJECTS AND METHODS The subjects (Table I) were eight healthy males from the staff of the laboratory. They were chosen as having body weights of approximately 60 kg (light subjects) and 80 kg (heavy subjects); none were particularly athletic nor did they use a bicycle regularly. The subjects were studied during the normal working day usually at the same times and starting not less than 1 hr after the end of the last meal. The exercise was performed on a Lanooy cycle ergometer, either sitting and pedalling with the legs or standing and cranking with the arms. In the former position the height of the saddle was adjusted for each subject; in the latter the height above * Present address: Institute of Pathophysiology, Medical School of Pecs, Hungary 211

2 212 Cotes, Allsopp and Sardi the floor of the axis of rotation was 1F04 m. On days when the subjects undertook progressive exercise, it comprised a single period of 11 or 12 min during which the rate of work was increased in steps at the end of the first, second or third minutes light heavy overall TABLE I mean {e 5 l6 7 l8 Cmean SUBJECTS FOR EXPERIMENT. Age yr mean 30 8 Weight kg ' *2 Height m 1'82 1*78 1*73 1* *88 1*75 1* of exercise at each work load; the average rate of increase of work over the period of exercise was always 10 watts per min, a rate recommended by the European Coal and Steel Community. On days when the subjects undertook steady state exercise, 120 Progressive 1*79 m I I Steady state CU 120. ::F.7.F. [] time (min) Fig. 1. Patterns of exercise adopted for the different sessions. Above: one minute, two minute and three minute progressive exercise. Below: steady state exercise. it comprised four periods each of 6 min duration, in the first experiment at 20, 40, 60 and 80 watts and in the second, 20, 40, 80 and 120 watts (fig. 1). Sufficient time was allowed between the periods of exercise for the cardiac frequency to return to its initial resting value.

3 Cardio-pulmonary Responses to Exercise 213 Ventilation was measured using a dry gas meter [Parkinson and Cowan] fitted with an optical integrator and counter which was read and reset each minute [Reynolds, 1968); the gas meter was positioned on the inspiratory side of the valve box and mouthpiece and was supplied with compressed air through a low pressure demand system. On inspiration the suction required for a flow rate of /min was 195 cm H20 and on expiration at the same flow rate the back pressure was 3-7 cm H20. Expiration was to atmosphere via a gas mixing chamber (capacity 4 1.) and an exit pipe from which a sample of mixed expired gas was drawn continuously through the gas analysers; these were a Servomex OA 137 paramagnetic analyser for oxygen and a Hartmann and Braun URAS 3 infra red analyser for CO2. The accuracy of analysis was that expected using these methods [Cotes and Woolmer, 1962]. Respiratory frequency was recorded on one channel of a Mingograf recorder using a thermistor mounted in the valve box; another channel of the recorder was used to monitor the cardiac frequency from electrodes applied to the chest. The cardiac frequency was also displayed on a heart rate integrator (Devices) which was used to monitor the frequency during recovery between periods of steady state exercise. Measurements were made for 5 min at rest and throughout each period of exercise. The analysis was confined to data collected for progressive exercise during the last minute at each work level, and for the steady state exercise during the last two minutes. The subjects were studied on 12, or in two cases 11 days; the first was a practice for which no results were recorded, and was followed by progressive exercise with the legs (4 days) when the rate of work was increased each minute, steady state exercise with the legs (1 day) and 1 min progressive and steady state exercise with the arms (2 and 1 davs respectively). These studies comprised the first experiment; it was undertaken in the Spring when the average temperature in the laboratory was 21 C. In the second experiment (mean laboratory temperature 240 C) the performance of the subjects was studied during 2 min and 3 min progressive exercise and steady state exercise with the legs; the order of exercise was random for each subject. The oxygen uptakes were calculated from the raw data by the standard method [Cotes, 1968] and a preliminary graphical analysis was carried out. For this purpose graphs were constructed for each exercise session on each subject of the relationships of the oxygen uptake to the rate of -ork, the ventilation and the cardiac frequency to the oxygen uptake and the ventilation to the tidal volume. For individual subjects the graphs were used to establish by eye the ranges over which these several relationships were linear. A regression equation was then calculated for each relationship over its linear range; this was based on the total data, except in the light subjects both during arm work and, in the second experiment, during leg work for the relationships of ventilation to oxygen uptake and to tidal volume. The coefficients and constant terms for all the relationships were later submitted to an analysis of variance. RESULTS Repetition of exercise. - In the first experiment the four replicate periods of progressive exercise with the legs yielded essentially similar results in the light subjects; in the heavy subjects the heart rate showed a decrease and the ventilation an increase over the first three days. The third and fourth days gave similar results and the mean data for these two days were used for the analysis. The two replicate periods of progressive exercise with the arms were completed by six subjects, in whom no material differences between the first and second days were observed. The data for the second VOL. LIV, NiO

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5 Cardio-pulmonary Responses to Exercise 215 day in these subjects and the first day in the other two subjects were used for the analysis. In the second experiment no systematic differences were 2.0 arm work _w loo ~ eg work progressive --- steady state I rate of work (watts) Fig. 2. Relationship of oxygen uptake (V02) to rate of work with the arms and legs for one minute progressive and steady state exercise. I 2.0 c I F arm work / /S - leg work '-A-, heavy - lighlt I rate of work (watts) Fig. 3. Relationship of oxygen uptake (V02) to rate of work during one minute progressive exercise for heavy and light subjects. observed over the three days, and the results, where they duplicated relationships which were also obtained in the first experiment, turned out to be similar. Thus the results reported below are independent of the order and of the

6 216 Cotes, Allsopp and Sardi a.,.- 'U.0 U Vo2 (l/ min) Fig. 4. Relationship of cardiac frequency (CF) to oxygen uptake (V02) during arm and leg work for progressive and steady state exercise. The data are those for the heavy subjects (cf. fig. 5). c 160 arm work / oa U).0 U V) 80 _ leg work hea vy light i 1.0 V 2 (1/min) I 2.Q Fig. 5. Relationship of cardiac frequency (CF) to oxygen uptake (V02) during arm and leg work for heavy and light subjects.

7 Cardio-pulmonary Responses to Exercise 217 experiment in which the measurements were made. They are summarized in Table II. Regression of oxygen uptake on rate of work. - The oxygen uptakes for work with the arms were higher than for work with the legs; during steady state exercise they were higher than during the 1 min progressive exercise for both types of work (p <0 01, fig. 2). Compared with the steady state, 45/ / arm work / / / g./5 leg work ~25 l heavy - _ light to2 (1/min) Fig. 6. Relationship of ventilation (VE) to oxygen uptake (VO2) during arm and leg work for progressive and steady state exercise. The data are those for the heavy subjects (cf. fig. 7). the oxygen uptakes during the 2 min progressive exercise with the legs for all subjects and during the 3 min progressive exercise for the light subjects were also lower. In addition, the slopes of the regression relationships were significantly steeper for steady state than for progressive exercise (mean values for 2 min and 3 min progressive and for steady state exercise respectively , and /min per watt, p<0.05). The oxygen uptakes were, on average, higher in the heavy than in the light subjects for work with both the arms and the legs (fig. 3), but these differences were significant only at the 10 per cent level of probability. Regression of cardiac frequency on consumption of oxygen. - The cardiac frequency for work with the arms was materially higher than for work with the legs. But for both types of work there was no difference between the 1 min progressive and the steady state exercise (fig. 4); for work with the legs this was also the case for 2 min and 3 min progressive exercise. Comparing the heavy and light subjects, the slope of the relationship was significantly steeper in the latter (p <0 01, fig. 5). l

8 218 Cotes, Allsopp and Sardi Regression of ventilation minute volume on consumption of oxygen. - The ventilation minute volume for work with the arms was materially higher than 45 arm work c I._ w 25 work progressive steady state Vo2 (I/ min) I Fig. 7. Relationship of ventilation (VE) to oxygen uptake (CV2) during arm and leg work for heavy and light subjects. 451 arm work c 25 leg work VT (1) Fig. 8. Relationship of ventilation (VE) to tidal volume (VT) during arm and leg work. for work with the legs. But for both types of work there was no difference between the 1 min progressive and the steady state exercise (fig. 6); for work with the legs this was also the case for the 2 min and 3 min progressive 9

9 Cardio-pulmonary Responses to Exercise 219 exercise. The slopes of the relationships were, on average, steeper for the light subjects (mean slopes for arm and leg work together respectively 22-0 and 25* 1, fig. 7); the regression coefficient for this slope on weight (-015 per kg) was significant only at the 10 per cent level of probability. Regression of ventilation on tidal volume. - The slope of the relationship was significantly steeper for work with the arms than for work with the legs (p <0 01, fig. 8); between progressive and steady state exercise and between heavy and light subjects no significant differences were observed. DISCUSSION The present results are similar to those reported by others for all the relationships for which details have been obtained from the literature; thus they are typical of their kind. They extend our understanding of the physiology of exercise with respect to the time of adjustment to an increase in the rate of work, the response to work with the arms as compared to that with the legs and the interactions between these responses and the body weights of the subjects. Progressive exercise. - The time for adjustment of oxygen uptake to an increase in work done with the legs in the present study is somewhat in excess of 3 min; this is consistent with the other observations [e.g. Shephard, 1967]. In addition, the regression coefficient for oxygen uptake on the rate of work with the legs is steeper for steady state than for progressive exercise; thus the time for adjustment increases with the severity of the exercise. This finding for moderate exercise differs from that for strenuous exercise where the time is materially less [Astrand and Saltin, 1961]. The difference may reflect the absence in moderate exercise of anaerobic metabolism contributing to vasodilatation in the vicinity of the active muscles. However, if this is the whole explanation the time for adaptation to the highest work levels included in the present study should be less for work with the arms than with the legs and for light than for heavy subjects; the present data do not support these corollaries, possibly because the range of work levels is too small. The regressions of ventilation and cardiac frequency on oxygen uptake during progressive and during steady state exercise have often been assumed to be identical. But the verification is of recent origin [Brouwers, 1967; Allen et al., 1968]; it is fully supported by the present findings. Thus it was to be expected that the regression of ventilation on tidal volume should be similar for the two procedures, and this turned out to be the case. The observations are of considerable practical use in permitting the rapid establishment of the regression relationships in individuals; they are also consistent with recent studies on the rate of adaptation to breathing carbon dioxide [Read and Leigh, 1967]. However, the apparent identity is to some extent an artefact due to the smoothing out of small incremental differences, and cannot be assumed to obtain for shorter time periods, or in the presence of disorders of function of the heart or lungs. Work with the arms and work with the legs. - The regression coefficient

10 220 Cotes, Allsopp and Sardi of oxygen uptake on rate of work with the arms for steady state exercise is very similar to that which may be calculated from the data of Bevegard [1966] and Sternberg [1967] and their colleagues. The constant term is larger by about /min, possibly due to our subjects performing the exercise standing rather than sitting. The relationship (Table II) may be of use for prediction of oxygen uptake (VO2) from the rate of work (W) during hand cranking, in the following form:- Vo0 (1./min) = W (Watts) (SD 0.14) This relationship neglects the role of body weight which is not significant (p <0 10) with the present small numbers of subjects but, by analogy with exercise using the legs, is likely to become so when more data are available for analysis [Cotes, 1969]. The higher values for ventilation and cardiac frequency in relation to consumption of oxygen during exercise with the arms than with the legs is in line with other observations [Asmussen and Nielsen, 1946]; the cause remains uncertain. It is unlikely to be lactacidwemia since the data relate to relatively mild exercise. The difference is probably due to other attributes of muscle size, which are considered below in relation to the effects of body weight. The values for cardiac frequency in relation to oxygen uptake in the present study are intermediate between those of the authors whose data for oxygen uptake are referred to above. The differences reflect the respective stroke volume and capacity for exercise of the subjects and are not of interest in their own right. The values for ventilation at low work levels are similar for the three sets of data; at higher work levels the present values are lower, possibly as a result of exclusion of the highest ventilations in some subjects where these lay above the critical point of Owles [1930, see Methods]. Thus the present data refer to aerobic work such as may be undertaken in industry. Since this entails exercise with the arms and back at least as often as with the legs, the absolute values may be of practical use for assessing the specification for a respirator, or the exposure to a polluted atmosphere. For this purpose the relationship of ventilation to oxygen uptake during arm work (Table II) may be used in the following form: VE (1./min) =28 0 Vo2 (1./min) - 18 (SD 4.4) where VE is ventilation minute volume at BTPS and Vo2 the consumption of oxygen at STPD. The finding that the regression of ventilation minute volume on tidal volume [Hey et al., 1966] is steeper for work with the arms than with the legs, is confirmed in the other data quoted [Bevegard, personal communication]. It may reflect a degree of fixation of the chest to enable the pectoral and other muscles to contribute to movement of the arms, and needs to be taken into account when considering the neuromuscular control of respiration. In our experience this consequence of arm work appears to exert a disproportionate effect in the case of patients with disordered function of the heart and lungs; it greatly aggravates their breathlessness.

11 Cardio-pulmonary responses to Exercise 221 Differences between heavy and light subjects: possible relation to muscle size. - The finding that oxygen uptake during progressive exercise with the legs and during exercise with the arms is probably greater in heavy than in light subjects is consistent with the results of previous studies for steady state exercise with the legs [Cotes, 1969]. It appears to reflect the different amounts of work done in moving the limbs and trunk. It was noted in the earlier investigations that the effect was not associated with corresponding differences for ventilation; instead, the ventilation for a constant rate of external work was independent of the body weights of the subjects, despite differences in their uptake of oxygen on this account. The finding carried the implication that the slope of the regression of ventilation on oxygen uptake was itself negatively correlated with body weight, but the effect was probably a small one. This is borne out by the results of the present study. Three possible mechanisms may be responsible. First, lactacidaemia due to anaerobic metabolism in the smaller muscles: this may be excluded for the reason given above. Second, the increased weight of the chest wall in the heavier subjects may cause a mechanical reduction in ventilation, as is observed, but to a greater extent, in obese patients. However, no effect of body weight on the relationship of the ventilation to the tidal volume was observed in the present study. Third, the differences in ventilation in relation to the uptake of oxygen may reflect an inverse correlation between the neurogenic drive to respiration [Dejours, 1964] and the size of the muscles performing the exercise. This has been demonstrated for the pressor response to exercise which is probably of reflex origin [Lind, McNicol and Donald, 1966]; it is possible but not proven that a similar mechanism obtains for ventilation. ACKNOWLEDGEMENTS We are greatly indebted to Mr. G. Berry for statistical advice. Dr. F. Sardi is also indebted to the Wellcome Trust for a research fellowship and to the Medical Research Council for laboratory facilities. The photographs were prepared by Messrs. R. Evans and R. T. Harris. REFERENCES ALiLEN, C., BANADE, M., DAVIES, C. T. M., Di PRAMPERO, P. E., HEDMAN, R., MERRIMAN, J., MYHRE, K., SHEPHARD, R. J., and SIMMONS, R. (1968). 'Physiological responses to step, bicycle ergometer, and treadmill exercise', J. Physiol. (Lond.), 196,131P-132P. AsM-usSEN, E., and NIELSEN, M. (1946). 'Studies on regulation of respiration in heavy work', Acta. physiol. scand., 12, ASTRAND, P. -O., and SALTIN, B. (1961) 'Oxygen uptake during the first minutes of lheavy muscular exercise', J. appl. Physiol., 16, BEVEGARD, S., FREYSCHRTSS, U., and STRANDELL, T. (1966). 'Circulatory adaptation to arm and leg exercise in supine and sitting position.' J. appi. Physiol., 21, BROUWERS, J. (1967). 'Comparison entre les consomnmations d'oxygene correspondant a des frequences cardiaques de 170, 160 et 150 par minute, mesurees au cycloergometre et au tapis roulant. Reproductibilite des mesures', Rev. Inst. Hyg. Mines, 22,

12 222 Cotes, Allsopp and Sardi COTES, J. E. (1968). 'Lung Function.' 2nd Edition. Blackwell Scientific Publications Oxford. COTES, J. E. (1969). 'Relationship of oxygen consumption, ventilation and cardiac frequency to body weight during standardized submaximal exercise in normal subjects', Ergonomics, 12. [In press.] COTEs, J. E., and WOOLMER, R. F. (1962). 'A comparison between twenty-seven laboratories of the results of analysis of an expired gas sample.' J. Physiol. (Lond.), 163, 36P-37P. DEJOURS, P. (1964). 'Control of respiration in muscular exercise.' In Fenn W. 0. and Rahn H. (ed). Handbook of Physiology, Section 3. Respiration, 1, pp Washington D.C., American Physiological Society. HEY, E. N., LLOYD, B. B., CUNNINGHAM, D. J. C., JUKES, M. G. M., and BOLTON, D. P. G. (1966). 'Effects of various respiratory stimuli on the depth and frequency of breathing in man', Resp. Physiol., 1, LIND, A. R., McNIcoL, G. W., and DONALD, K. W. (1966). 'Circulatory adjustments to sustained (static) muscular activity.' In Physical Activity in Health and Disease. Urniversitetsforlaget, Oslo. MULLER, E. A. (1950). 'Ein Leistungs-Pulsindex als Mass det Leistungsfahigkeit', Arbeitsphysiologie, 14, NAGLE, F. J., BLAKE, B., and NAUGHTON, J. P. (1965). 'Gradational step tests for assessing work capacity', J. appl. Physiol., 20, OwLEs, W. H. (1930). 'Alterations in the lactic acid content of the blood as a result of light exercise and associated changes in the CO2 -combining power of the blood and in the alveolar CO2 pressure', J. Physiol. (Lond.), 69, 214. READ, D. J. C., and LEIGH, J. (1967). 'Blood-brain tissue Pco2 relationships and ventilation during rebreathing', J. appl. Physiol., 23, REYNOLDS, J. A. (1968). 'Recording gas meter for measiring pulmonary ventilation', J. Physiol. (Lond.), 194, 52P-54P. SHEPHARD, R. J. (1967). 'The prediction of "maximal" oxygen consumption using a new progressive step test', Ergonomics, 10, STERNBERG, J., ASTRAND, P.-O., EKBLOM, B., ROYCE, J., and SALTIN, B. (1967). 'Hemodynamic response to work with different muscle groups, sitting and supine', J. appl. Physiol., 22,