HEART RATE PREDICTIONS OF EXERCISE INTENSITY DURING ARM, LEG AND COMBINED ARM/LEG EXERCISE

Transcription

1 J. Human Ergol., 10: , 1981 HEART RATE PREDICTIONS OF EXERCISE INTENSITY DURING ARM, LEG AND COMBINED ARM/LEG EXERCISE Kiyokazu KITAMURA, Keiji YAMAJI, and Roy J. SHEPHARD Laboratory for Exercise Physiology, Toyama University, Gofuku, Toyama, Japan School of Physical and Health Education and Department of Preventive Medicine and Biostatistics, Faculty of Medicine, University of Toronto, 320 Huron Street, Toronto, Ontario, Canada M5S 1A1 Differences in the heart rate/ oxygen consumption relationship were examined for three different forms of cycle ergometry (leg, arm, and combined leg/arm exercise), using as subjects a group of young healthy adults (6 males, 7 females). Maximum oxygen intake showed the expected variation with active muscle mass, discrepancies between the three modes of exercise being larger in female than in male subjects. A small muscle mass was also associated with a lower terminal heart rate, but a higher terminal respiratory minute volume. During submaximal exercise, differences in the heart rate/percent maximum oxygen intake line were sufficiently large to preclude use of a single relationship in prescribing various forms of recreational activity. However, at higher intensities of effort a single (leg work) line could be used if plotted in the format percent maximum heart rate versus percent maximum oxygen intake. Unfortunately, this relationship also varied with exercise mode during light work, and it is thus unsuitable for the prediction of exercise intensity in industrial situations. The well-known linear relationship between heart rate and oxygen intake or relative oxygen intake remains the most popular method of regulating the intensity of endurance training. Nevertheless, many problems have been recognized in exploiting this relationship, whether as a basis for exercise prescription, or in industrial surveys of energy expenditure. The slope of the line is influenced by the age of the subjects (IzuKI et al., 1976; YAMAJI et al., 1978), their sex (ASTRAND and YHMING, 1954; ASTRAND et al., 1964; STENBERG, 1966), ambient oxygen pressure (EKBLOM et al., 1975; FLANDROIS and LACOUR, 1971; HORSTMAN et a!., 1979), the mode of exercise (ASMUSSEN and HEMMINGSEN, 1958; STENBERG, Received for publication February 18,

2 152 K. KITAMURA, K. YAMAJI and R. J. SHPPHARD 1966; SHEPHARD, 1968), training (SALTIN et al., 1976; YAAJI et al., 1978), environmental temperature (SALTIN et al., 1968), administration of drugs or endogenous release of catecholamines (AsTRAND, 1973; HOWLEY et al., 1970), and various biorhythms (YAMAJI et al., 1982). The purpose of the present experiments was to evaluate differences in the heart rate/oxygen intake relationship during arm, leg and combined arm/leg exercise, with a view to developing a technique that could minimize the influence of exercise mode when predicting the intensity of physical activity. METHODS The subjects were healthy students (6 males and 7 females). Some of the group were participating in competitive athletics, and all had previous experience of leg ergometry. They were not familiar with arm ergometry, and for this reason were allowed at least two practice runs with this type of activity. The physical characteristics of the subjects were : age and years, height cm and cm, and weight and kg, for men and women, respectively. All exercise was performed using a mechanically-braked cycle ergometer (Monark/Von Dobeln). The pedal frequency was held to a constant value of 60 rpm. During arm exercise, the ergometer was positioned at chest level, with hand-cranks situated some 75 cm above the floor. The loading was increased at one-minute intervals, until subjective exhaustion was reached; stages of 15 watts were used for arm exercise, and 30 watts for leg exercise. During combined arm/leg exercise, the intensity of the arm component was increased in 15 watt stages until 50 % of the arm maximum oxygen intake was attained. The arm loading was then held constant, and leg work was increased in 30 watt stages until exhaustion was reached. The oxygen intake and the heart rate were recorded each minute of exercise until exhaustion. Expired gas was collected into a Douglas bag via a low-resistance McKerrow-type value box and a short length of smooth-walled tube (internal diameter 33 mm). The volume of gas collected was measured by means of a dry gas meter, while the oxygen and carbon dioxide content were assessed by gas chromatography (KITAMURA et al., 1980). The heart rate was measured from an electrocardiogram (CM5 chest leads). The highest oxygen intake and heart rate attained were accepted as the maximum oxygen intake and the maximum heart rate for a particular mode of exercise. RESULTS Maximal effort tests. The maximum oxygen intakes, heart rates, and respiratory minute volumes attained during the three modes of exercise are shown in Tables 1 and 2. Considering the leg exercise value for a given individual as

3 HEART RATE PREDICTIONS 153 Table 1. Criteria for attainment of maximal oxygen intake (Vo2max) in males.1 00%, the maximum oxygen intake during combined arm/leg effort average 118 for males (range %) and 112% for females (range %). The corresponding arm exercise values were 70 % (45-85 %) for males, and 61 % (48-75 %) for females. The maximal heart rates and maximal respiratory minute volumes were also greater for combined exercise, and less for arm exercise than for leg exercise. Statistical analysis (Table 3) showed that these various differences were significant at levels of probability ranging from 0.05 to Sub-maximal heart rate responses. Individual subjects all showed significant linear relationships between heart rate and oxygen intake for a given mode of exercise (Fig. 1). As anticipated, the lines differed according to the exercise mode (Fig. 2). At any given percentage of the maximum oxygen intake as determined for a given type of activity, the heart rate was higher for combined exercise than for leg exercise; the latter was in turn higher than the corresponding arm exercise reading. The relationship between the relative heart rate (percent of maximum for a given exercise mode) and the relative oxygen intake was also highly significant (p<0.001) in both sexes (Fig. 3). At light work loads (20% of the relative maximum oxygen intake), the relative heart rate lines diverged substantially from each other (51 to 60% of heart rate maximum) for the three types of exercise, but at 80 % of the relative maximum oxygen intake, the various regressions con-

4 154 K. KITAMURA, K. YAMAJI and R. J. SHEPHARD Table 2. Criteria for attainment of maximal oxygen intake (Vo2max) in females. Table 3. Statistical analyses of differences. A, arm exercise; L, leg exercise; L+A, combined leg and arm exercise. p values are calculated on interindividual differences. * p<0.05; ** p<0.01; * p< verged to % of the corresponding maximal heart rate (Fig. 3). DISCUSSION Maximum oxygen intake and exercise mode Unfortunately, traditional methods of assessing maximum oxygen intake readings cannot be applied to arm work. A substantial proportion of subjects

5 HEART RATE PREDICTIONS Fig. 1. The relationship between heart rate and oxygen intake in subject K.Y. Fig. 2. Heart rate at submaximal exercise in relation to relative V o2max (% Vo2max). fails to demonstrate an oxygen plateau, and because of the small active muscle mass neither the respiratory gas exchange ratio nor blood lactate determinations reach the levels anticipated during maximum leg work. Nevertheless, given that all tests were carried to voluntary exhaustion, there is no reason to suppose that there were systematic differences of motivation between the three modes of exercise. We may thus accept the relative values for the three types of activity with reasonable confidence.

6 156 K. KITAMURA, K. YAMAJI and R. J. SHEPHARD Fig. 3. The relationship between relative maximal heart rate (% HRmax) and relative maximal oxygen intake (% Vo2max). Table 4. Comparisons of Vo2max attained during arm, leg and arm/leg exercise. * The Vo 2max during arm and combined arm/leg exercise are shown as a percent of Vo2max during leg exercise. Results for the males are much as described by other authors (BERGH et al., 1976; SECHER et al., 1974; SIMMoNs and SHEPHARD, 1971); relative to the leg ergometer values, maximum oxygen intakes were 30 % lower for arm exercise alone, and 18 % higher for combined exercise (Table 4). Possibly because of a limited arm muscle mass, the average arm value for the women is even lower (61 of leg), and the addition of arm work makes a smaller (12%) contribution to the consumption of oxygen induced by leg work. An interesting feature of the present experiments is the clear demonstration of differences in maximum heart rate and respiratory minute volume for the three patterns of work. Again, there is a sex difference. In the male subjects, the maximal heart rate is 6 % lower for arm work, and 3 % higher for combined

7 HEART RATE PREDICTIONS 157 work, while in the women the discrepancies amount to -14 % and +3 %. Corresponding figures for the maximum respiratory minute volume are -26 % and +29 % (male) and -36 % and x-18 % (female). The ventilatory differences presumably reflect the active muscle mass (S0L and SINNING, 1980), and thus the blood lactate concentration in the three types of work, but the heart rate readings suggest that arm exercise is halted before the heart has reached its maximum potential performance. Various authors (reviewed by SHEPHARD, 1977) have suggested that the dependence of maximum oxygen intake upon the exercise mode invalidates this criterion of endurance performance. Even leg exercise is unable to elicit the combined arm/leg reading if a cycle ergometer is used for testing. However, this is a criticism of ergometer design rather than maximum oxygen intake as a concept. If exercise is performed on a treadmill rather than a cycle ergometer, little additional oxygen transport is induced by simultaneous arm exercise (TAILOR et al., 1955; STENEERG et al., 1967; PIRNAY et al., 1971; HOCKEY, 1980). The usual cycle ergometer is propelled almost exclusively upon the quadriceps muscle. Improved designs increase the effective muscle mass by devices such as toe straps or allowing the subject to stand on the pedals (KELLY et al., 1980). The discrepancy between cycle ergometer and treadmill readings is then greatly reduced. While maximum oxygen intake remains a viable concept, the present data calls into question the view that oxygen transport is always limited centrally, by the pumping ability of the heart (ASTRAND and SALTIN,1961; CLAUSEN, et a1.,1973 ; REYBROUCK et al., 1975; SHEPHARD, 1977). The mass of active muscle also seems to be implicated in the result that is obtained, at least to the extent that some critical volume is reached (PAR-OR and ZWIREN, 1975; GLESER et al., 1974; SECHER et al.,1974). The limitation of effort does not seem to be imposed directly by the availability of tissue enzymes, since during training maximum oxygen intake and enzyme activity levels increase at widely disparate rates. However, it is conceivable that when a small group of muscles is activated, a combination of effort at a high percentage of maximum voluntary force (KAY and SHEPHARD, 1969) and a small vascular bed facilitates an intramuscular accumulation of lactate, with an early inhibition of glycolysis (phosphorylase/fructokinase) and consequent exhaustion. An alternative hypothesis may be that attempts to perfuse the active muscles generate an excessive rise of systemic blood pressure, with restriction of cardiac stroke volume, and reflex limitation of maximum heart rate. Finally, the small muscle bed may provide an inadequate venous return to sustain the potential cardiac performance. Plainly further experimentation, including determinations of intramuscular lactate concentration, will be needed to distinguish between these several possibilities. Heart rate in sub-maximal exercise The higher heart rate occurring during arm work has been noted by many

8 158 K. KITAMURA, K. YAMAJI and R. J. SHEPHARD previous investigators (for example ASMUSSEN and HEMMINGSEN, 1958; BEVEGARD et al., 1966; BOBBERT, 1960). Plainly, if the heart rate/percent maximum oxygen intake line is to be used in assessing the intensity of effort developed in sport, recreation, or industrial tasks, it is important that the calibration line is based on an equivalent mass of active muscle. For the runner, leg exercise on the cycle ergometer can be used, but the treadmill is preferable. n the other hand, activities such as kayaking need a calibration line based upon arm cranking, while cross-country skiing may demand a line based upon combined arm and leg exercise. This is not a serious problem when advising an athlete of international calibre who is interested in only one form of exercise, but it is a source of difficulty when advising the recreational performer who enjoys performing several types of activity at different seasons of the year. The use of a single (leg work) calibration line can lead to a substantial over-estimation of exercise intensity in arm work, and a corresponding under-estimate in combined exercise. Predictions become even less realistic unless account is taken of such variables as age, cigarette smoking, isometric activity, and high environmental temperatures. It is obviously impracticable to base exercise prescription upon a whole series of task-specific calibration lines. One possible solution suggested by the present research is to use the line relating percent of maximum heart rate to percent of maximum oxygen intake. Environmental errors will remain, but nevertheless, the heart rate estimate of exercise intensity will then have an acceptable range of error. It should be emphasized that this conclusion applies only to the upper end of the calibration line, as encountered in vigorous voluntary exercise. The relative heart rate does not help the task of the ergonomist who wishes to estimate more moderate intensities of industrial work (SHEPHARD, 1968). Nor is the new approach suitable for exercise prescription in the cardiac patient; in such individuals, the critical factor is the cardiac work-load, and this is indicated most clearly by the absolute heart rate or the heart rate/blood pressure product (JGRGENSEN, 1970). REFERENCES ASMUSSEN, E., and HEMMINGSEN, I. (1958) Determination of maximum working capacity at different ages in work with the legs and arms. Scand. J. Clin. Lab. Invest., 10: ASTRAND, P.-O. (1973) Physiology of exercise and physical conditioning in normals. Schweiz. Med. Wochenschr.,103: A5TRAND, P.-O., CUDDY, T. E., SALTIN, B., and STENBERG, J. (1964) Cardiac output during submaximal and maximal work. J. App!. Physiol.,19: AsTRAND, P.-O. and RYHMING, I. (1954) A nomogram for calculation of aerobic capacity from pulse rate during submaximal work. J. Appl. Physiol., 7: ASTRAND, P.-O. and SALTIN, B. (1961). Maximal oxygen and heart rate in various types of muscular activity. J. Appl. Physiol.,16: BAR-OR, O. and ZWIREN, L. D. (1975) Maximal oxygen consumption test during arm exercisereliability and validity. J. Appl. Physiol., 38:

9 HEART RATE PREDICTIONS 159 BERGH, U., KANSTRUP, I. L., and EKBLOM, B. (1976) Maximal oxygen uptake during exercise with various conbinations of arm and leg work. J. Appl. Physiol., 41: BEVEGARD, S., FREYSCHUSS, U., and STRANDELL, T. (1966) Circulatory adaptation to arm and leg exercise in supine and sitting position. J. Appl. Physiol., 21: BOBBERT, A. C. (1960) Physiological comparisons of three types of ergometry. J. Appl. Physiol.,15: CLAUSEN, J. P., KLAUSEN, K., RASMUSSEN, B., and TRAP-JENSEN, J. (1973) Central and peripheral circulatory changes after training of the arms or legs. Am. J. Physiol., 225: EKBLOM, B., HUOT, R., STEIN, E. M., and THORSTENSSON, A. T. (1975). Effect of changes in arterial oxygen content on circulation and physical performance. J. Appl. Physiol., 39: FLANDROIS, R. and LACOUR, J. R. (1971) The prediction of maximal oxygen intake in acute moderate hypoxia. Int. Z. Angew. Physiol., 29: GLESER, M. A., HORSTMAN, D. H. and MELLO, R. P. (1974) The effect on Vo2max of adding arm work to maximal leg work. Med. Sci. Sports, 6: HOCKEY, R. V. (1980) Comparison of max V02 involving the treadmill and the bicycle ergometrr with and without adjustable ski-poles. Med. Sci. Sports, 12:115. HORSTMAN, D. H., WEISKOPF, R., and ROBINsoN, S. (1979) The nature of the perception of effort at sea level and high altitude. Med. Sci. Sports, 11: HOWLEY, E. T., SKINNER, J. S., MENDEZ, J., and BUSKIRK, E. R. (1970) Effect of different intensities of exercise on catecholamine excretion. Med. Sci. Sports, 24: JORGENSEN, C. R. (1970) Coronary blood flow and myocardial oxygen consumption in man. In Physiology of Fitness and Exercise, ed. by ALEXANDER, J. F., SERPASS, R. C., and TIPTON, C. M., Athletic Institute, Chicago, pp KAY, C. and SHEPHARD, R. J. (1969) On muscle strength and the threshold of anaerobic work. Int. Z. Angew. Physiol., 27: KELLY, J. M., SERFASS, R. C., and STULL, U. A. (1980) Elicitation of maximum oxygen uptake from standing bicycle ergometry. Res. Quart., 51: KITAMURA, K., FUKUDA, A., YAMAJI, K., and ARISAWA, K. (1980) A practical application of measuring oxygen by the gas-chromatography. Jpn. J. Phys. Educ., 25: OIZUKI, T., YAMAJI, K., and ARISAWA, K. (1976) Predictions of exercise intensity using HR/ Vo2max during running and walking. J. Health Phys. Educ. Rec., 26: PENDERGAST, D., CERRETHELLI, P., and RENNIO, D. W. (1979) Aerobic and glycolytic metabolism in arm exercise. A. Appl. Physiol., 47: PIRNAY, F., DEROANNE, R., MARECHAL, R., DUJARDIN, J. and PETIT, J. M. (1971) Consommation maximum d'oxygen daps differents types d'exercise musculaire. Arch. Int. Physiol. Biochim., 79: REYBROUCK, T., HEIGENHAUSER, G. F., and FAULKNER, J. A. (1975) Limitations of maximum oxygen uptake in arm, leg and combined arm-leg ergometry. J. Appl. Physio!., 38: SALTIN, B., BLOMQVIST, B., MITCHEL, J. H., JOHNSON, R. L., WILDENTHAL, K., and CHAPMAN, C. B. (1968) Response to submaximal and maximal exercise after bed rest and training. Circulation, 38 (Suppl. 7): 19-20, 40-41, SALTIN, B., NAZAR, K., COSTILL, D. L., STEIN, E., JANSSON, E., ESSEN, B., and GOLLNICK, P. D. (1976) The nature of the training response; peripheral and central adaptations to onelegged exercise. Acta Physiol. Scand., 96: SECHER, N. H., LARSEN, N. R., BINKHORST, R. A., and PETERSEN, F. B. (1974) Maximal oxygen uptake during arm cranking and combined arm plus leg exercise. J. Appl. Physiol., 36: SHEPHARD, R. J. (1968) Practical indices of metabolic activity; An experimental comparison of pulse rate and ventilation. Int. Z. Angew. Physiol., 25:

10 160 K. KITAMURA, K. YAMAJI and R. J. SHEPHARD SHEPHARD, R. J. (1977) Endurance Fitness, 2nd ed., University of Toronto Press, Toronto. SIMMONS, R., and SHEPHARD, R. J. (1971) Measurement of cardiac output in maximum exercise. Application of an acetylene rebreathing method to arm and leg exercise. Int. Z. Angew. Physiol., 29: SOL, N., and SINNING, W. (1980) Physiological responses arm and leg work adjusted for active muscle volume. Med. Sci. Sports, 12: 116. STENBERG, J. (1966) The significance of the central circulation for the aerobic work capacity under various conditions in young healthy persons. Acta Physiol. Scand., 68, Suppl STENBERG, 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: TAYLOR, H. L., BUSKIRK, E. R., and HENSCHEL, A. (1955) Maximal oxygen intake as an objective measure of cardio-respiratory performance. J. Appl. Physiol., 8 : YAMAJI, K., MIYASHITA, M., and SHEPHARD, R. J. (1978) Relationship between heart rate and relative oxygen intake in male subjects aged 10 to 27 years. J. Human.Ergol., 7: YAMAJI, K., SAKAMOTO, H., NAKAGUCHI, M., KITAMURA, K., and SHEPHARD, R. J. (1981) Biological rhythms of PWC170 and maximal oxygen intake. J. Human.Ergol., 10: