ACYCLE ERGOMETER, AS WELL AS a treadmill, are

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1 1024 Comparison of Cardiovascular Responses Between Upright and Recumbent Cycle Ergometers in Healthy Young Volunteers Performing Low-Intensity Exercise: Assessment of Reliability of the Oxygen Uptake Calculated by Using the ACSM Metabolic Equation Masakazu Saitoh, MS, Atsuhiko Matsunaga, PhD, Kentaro Kamiya, MS, Misao N. Ogura, MS, Junko Sakamoto, MS, Ryusuke Yonezawa, MS, Yusuke Kasahara, MS, Hiroyuki Watanabe, MS, Takashi Masuda, MD, PhD ABSTRACT. Saitoh M, Matsunaga A, Kamiya K, Ogura MN, Sakamoto J, Yonezawa R, Kasahara Y, Watanabe H, Masuda T. Comparison of cardiovascular responses between upright and recumbent cycle ergometers in healthy young volunteers performing low-intensity exercise: assessment of reliability of the oxygen uptake calculated by using the ACSM metabolic equation. Arch Phys Med Rehabil 2005;86: Objectives: To clarify (1) differences in cardiovascular response during low-intensity exercise in the upright versus the recumbent position, and (2) whether the oxygen uptake (V O2 ) calculated by the American College of Sports Medicine (ACSM) metabolic equation reflects the actual V O2 at lowintensity testing. Design: Repeated-measures comparison study. Setting: University research laboratory. Participants: Thirty-one healthy, young volunteers (age, 23 2y). Interventions: Not applicable Main Outcome Measures: Blood pressure, rate pressure product (RPP), V O2, oxygen pulse, carbon dioxide output (V CO2 ), and ventilatory equivalent (V E) were measured during graded exercise testing using upright and recumbent cycle ergometers. The estimated V O2 was calculated by using the ACSM metabolic equation. Results: Systolic blood pressure, RPP, V O2, oxygen pulse, V CO2, and V E at 15 or 30W were significantly higher in the recumbent position than in the upright one (P.05), however, no significant differences were observed at 50 and 70W. The estimated V O2 during exercise was significantly higher than the actual one, at every level of intensity, from 15 to 70W (P.05). Conclusions: Cardiovascular responses should be carefully monitored even during low-intensity exercise using a recumbent cycle ergometer. The V O2 estimated using the ACSM From the Department of Angiology and Cardiology, Graduate School of Medical Sciences (Saitoh, Sakamoto, Yonezawa, Kasahara) and Department of Rehabilitation, School of Allied Health Sciences (Matsunaga, Ogura, Watanabe, Masuda), Kitasato University; and Rehabilitation Center, Kitasato University Hospital (Kamiya), Kanagawa, Japan. Supported in part by a grant-in-aid for scientific research (grant no ) from the Ministry of Education, Science, and Culture in Japan. No commercial party having a direct financial interest in the results of the research supporting this article has or will confer a benefit upon the authors(s) or upon any organization with which the author(s) is/are associated. Reprint requests to Takashi Masuda, MD, PhD, Dept of Rehabilitation, School of Allied Health Sciences, Kitasato University, Kitasato, Sagamihara, Kanagawa, , Japan, tak9999@med.kitasato-u.ac.jp /05/ $30.00/0 doi: /j.apmr metabolic equation did not reflect the actual V O2 during lowintensity exercise at 70W or less. Key Words: Cardiovascular physiology; Ergometry; Exercise; Rehabilitation by American Congress of Rehabilitation Medicine and the American Academy of Physical Medicine and Rehabilitation ACYCLE ERGOMETER, AS WELL AS a treadmill, are among the most popular devices used in clinical exercise testing or programs of cardiac rehabilitation. Training on a treadmill, to simulate natural walking, is the most common form of physiologic stress and is suitable to load work for the assessment of oxygen uptake (V O2 ), as compared with a cycle ergometer. 1 However, the cycle ergometer allows for a non weight-bearing exercise in which the work can be properly varied by minute adjustments in the workload and is a safer device for older persons because accidental falls rarely occur when using a cycle ergometer as compared with a treadmill. 1 The cycle ergometer mainly allows for 2 types of exercise training: one is the ordinary upright type and the other a recumbent one that more recently is used by older persons (fig 1). There are many reports 2-4 on the differences in the cardiovascular responses between upright and recumbent ergometry when high-intensity exercise is performed by healthy volunteers or patients with coronary artery disease (CAD). 2-4 It is generally recognized that heart rate and V O2 decrease more during submaximal exercise in the recumbent position than in the upright position. The reasoning is that, in the recumbent position, keeping the leg up augments venous return, increases stroke volume, and mobilizes the lower mass of the muscles during pedaling, as compared with the upright cycle ergometer. 3-6 When a cardiac rehabilitation program advances from walking on the floor to exercising on cycle ergometers, a lowintensity workload is prescribed at first for patients with acute myocardial infarction (AMI). In our study, 10 to 15W was the lowest and reliable workload in cycle ergometers and is equivalent to a workload of a 300-m walk, as assessed by using the metabolic equation recommended by the American College of Sports Medicine (ACSM) for cycle ergometry and walking. 1 However, we have observed and previously reported that when the patients exercised using a cycle ergometer for the first time after AMI, 40% of them show an excessive increase of systolic blood pressure (SBP) during the exercise, even at a low intensity ( 15W). We have noted that cardiovascular responses should be carefully monitored in the same way as it is during a 300-m walk on the floor in phase I cardiac rehabilitation. 7,8 In addition, there are only a few detailed reports investigating

2 CARDIOVASCULAR RESPONSES IN BICYCLE EXERCISE, Saitoh 1025 Fig 1. (A) Upright cycle ergometer and (B) recumbent cycle ergometer. cardiovascular responses during low-intensity exercise using a cycle ergometer, both in patients with CAD and in healthy, young volunteers On the other hand, the ACSM metabolic equation, which is widely used to prescribe a standard exercise training, estimates V O2 during exercise using a cycle ergometer and is reported to reflect precisely the actual V O2 measured at submaximal aerobic exercise at a load of more than 50W. 1 The ACSM metabolic equation is also applied when the workload is less than 50W, because it is convenient to assess the V O2 in patients who cannot perform the submaximal exercise test because of cardiopulmonary, neurologic, or orthopedic limitation. 1 However, it has not been established whether the ACSM metabolic equation is applicable to estimate the V O2 in patients prescribed low-intensity exercise using a cycle ergometer. The purpose of our study was to clarify (1) whether the cardiovascular responses are influenced by the position during exercise in healthy, young volunteers performing low-intensity exercise using upright and recumbent cycle ergometers and (2) whether the estimated V O2 calculated by the ACSM metabolic equation reflects the actual V O2 measured during low-intensity exercise. METHODS Participants Thirty-one healthy, young volunteers, aged 21 to 28 years (15 men, 16 women; mean age, 23 2y; mean body weight, kg), participated in our study. The study protocol was approved by the Ethics Committee of Kitasato University, and informed consent was obtained from each subject after detailed explanation of the protocol. All volunteered to participate and none received monetary compensation. Procedure All subjects performed the exercise test using an upright cycle ergometer a and a recumbent ergometer b in a thermoneutral (24 26 C) laboratory (see fig 1). Two days after undergoing the exercise test with 1 type of cycle ergometer, they performed the test with the other type of ergometer. To avoid the influence of test order, all subjects were randomly divided into 2 groups and then the order of testing of the upright or recumbent cycle ergometer was assigned to each group. The height of the seat was adjusted to each subject in both ergometers, so that a slight bending of the knee was kept in the maximal extension of the leg, before the feet were fitted for the pedals of the ergometer with a toe-clip. The backrest of the recumbent cycle ergometer was inclined at an angle of 110 to serve as support for the upper body. Study Protocol The graded exercise test consisted of 5 stages: rest and 3-minute workloads of 15, 30, 50, and 70W. The exercise workload was increased step by step from 15 to 70W in order, after sitting at rest for 5 minutes (fig 2). In both the upright and recumbent cycle ergometers, the pedaling frequency was main- Fig 2. The exercise protocol.

3 1026 CARDIOVASCULAR RESPONSES IN BICYCLE EXERCISE, Saitoh V E among the 5 stages and between the upright and recumbent position. Similarly, a 2-way ANOVA for repeated-measures (3 means vs 5 stages) was used in V O2 among the 5 stages and between the actual and estimated V O2. If an F ratio was significant, the Tukey multiple range test was applied to find the significant differences between the actual and estimated V O2. All values are expressed as the mean standard deviation (SD) and a P value less than.05 was considered statistically significant. The descriptive analyses were performed by using SPSS, 11.0J software, f for Windows. Fig 3. Change in heart rate during exercise in the upright and recumbent position. Values are mean 1 SD. Legend: Œ, heart rate in the upright position;, heart rate in the recumbent position. Abbreviation: HR, heart rate. tained constant at 50rpm during the exercise test. Heart rate and electrocardiographic activity were continuously monitored by using an electrocardiography monitoring system, c and SBP and diastolic blood pressure (DBP) were measured every 1 minute using an automatic manometer with the cuff method. d The V O2, carbon dioxide output (V CO2 ), and ventilatory equivalent (V E) were measured breath by breath by using a gas analyzer e throughout the test. The values of heart rate (HR), blood pressure, V O2,V CO2, and V E obtained 3 and 4 minutes after sitting at rest were averaged as the baseline values and those obtained 3 minutes after the beginning of each workload were indicated as representative values for that workload. By using these values, we calculated the rate pressure product (rate pressure product [RPP] HR SBP) as myocardial V O2 11 and the oxygen pulse (oxygen pulse V O2 /HR) as stroke volume. 12,13 The ACSM Metabolic Equation The V O2 estimated by using the ACSM metabolic equation consists of 3 parts in the case of exercise in a cycle ergometer: the V O2 used at the resting position on the seat and for unloaded cycling, and the V O2 that increases in proportion to the external workload. The V O2 in the resting position and unloaded cycling at 50 to 60rpm is estimated to be approximately 3.5mL kg 1 min 1, respectively. Therefore, the estimated V O2 at rest was 3.5mL kg 1 min 1 in our study. The external workload was calculated as a work rate (kpm/min) that consisted of 3 components: pedaling frequency (in rpm), the distance of cycling in a revolution of the flywheel (in meters), and the resistance set on the flywheel (in kpm). The ACSM metabolic equation is: Estimated V o 2 (ml kg 1 min 1 ) 1.8(mL kg 1 m 1 ) work rate (kpm min) body weight (kg) 7.0 (1) The estimated V O2 calculated by using the ACSM metabolic equation was compared with the actual V O2 measured by using a gas analyzer in both the upright and recumbent positions. Statistical Analysis A 2-way analysis of variance (ANOVA) for repeated-measures (2 means vs 5 stages) was used to analyze the differences in heart rate, SBP, DBP, RPP, V O2, oxygen pulse, V CO2, and RESULTS The heart rate at each workload is shown in figure 3. The heart rate increased gradually regardless of the position, in proportion to the workload. However, there were no significant differences in heart rate at any workload between the upright and recumbent position. The SBP and DBP at each workload are shown in figure 4. Although SBP at rest, 50 and 70W showed no significant differences between the upright and recumbent position, those at 15 and 30W were significantly higher in the recumbent position (both P.05). There were no significant differences in DBP at any workload between the upright and recumbent position. The RPP at each workload is shown in figure 5. Although RPP at rest, 50 and 70W showed no significant differences between the upright and recumbent position, those at 15 or 30W was significantly higher in the recumbent position (both P.05). Figure 6 shows the actual V O2 measured during exercise in the upright and recumbent cycle ergometers and the estimated V O2 calculated by using the ACSM metabolic equation. Although the actual V O2 at rest, 50W, and 70W showed no significant differences between the recumbent and upright position, those at 15 and 30W were significantly higher in the recumbent position (both P.05). The estimated V O2 was significantly higher at every workload than the actual V O2 measured during the exercise either in the upright or recumbent cycle ergometer (all P.05). The oxygen pulse at each workload is shown in figure 7. Although the oxygen pulse at rest, 50W, and 70W showed no significant differences between the upright and recumbent po- Fig 4. Change in SBP and DBP during exercise in the upright and recumbent position. Values are mean 1 SD. Legend: Œ, blood pressure in the upright position;, blood pressure in the recumbent position. *P<.05 between upright and recumbent position.

4 CARDIOVASCULAR RESPONSES IN BICYCLE EXERCISE, Saitoh 1027 Fig 5. Change in RPP during the exercise in the upright and recumbent position. Values are mean 1 SD. Legend: Œ, RPP in the upright position;, RPP in the recumbent position. *P<.05 between upright and recumbent position. Fig 7. Change in oxygen pulse during exercise in the upright and recumbent position. Values are mean 1 SD. Legend: Œ, oxygen pulse in the upright position;, oxygen pulse in the recumbent position. Abbreviation: O 2 pulse, oxygen pulse. *P<.05 between upright and recumbent position. sition, those at 15 and 30W were significantly higher in the recumbent position (both P.05). The V CO2 at each workload is shown in figure 8. Although there were no significant differences in the V CO2 at rest, 50W, and 70W between the 2 positions, the V CO2 at 15 or 30W was significantly higher in the recumbent position than in the upright one (both P.05). The V E at each workload is shown in figure 9. Although there were no significant differences in the V E at rest, 30W, 50W, and 70W between the 2 positions, the V E at 15W was significantly higher in the recumbent position than in the upright one (P.05). DISCUSSION There are many reports documenting the difference in cardiovascular responses between the upright and recumbent position in healthy volunteers or patients with CAD who perform exercise at submaximal intensity or higher using a cycle ergometer. 2-4,14,15 Consequently, it has been pointed out that heart rate, RPP, and V O2 are lower and oxygen pulse is higher in the recumbent position than in the upright one during exercise at submaximal intensity. 2-4,14 These changes mainly derive from differences in venous return and the mobilized muscle mass of the trunk and extremities between the upright and recumbent position. The augmented venous return in the recumbent position contributes to an increase of stroke volume, resulting in the suppression of heart rate elevation, whereas the oxygen demand is the same as in the upright position. 3,4 The muscles of the hamstrings and quadriceps are principally used for pedaling during exercise in a recumbent cycle ergometer because the muscles of the trunk and upper extremities are limited to support the body. On the contrary, the muscles of the trunk and upper extremities bear the pedaling during exercise in an upright cycle ergometer, as well as the hamstrings and quadriceps. 3 Therefore, the V O2 was lower during exercise in the recumbent cycle ergometer at the same workload. However, we failed to show significant differences in heart rate, blood pressure, RPP, V O2, or oxygen pulse between the upright and recumbent position during exercise at submaximal Fig 6. Change in V O2 during exercise in the upright and recumbent position. Values are mean 1 SD. Legend: Œ, V O2 in the upright position;, V O2 in the recumbent position;, estimated V O2 calculated by using the ACSM metabolic equation. *P<.05 between upright and recumbent position. P<.05 between the V O2 measured in the upright position and the estimated V O2. P<.05 between the V O2 measured in the recumbent position and the estimated V O2. Fig 8. Change in V CO2 during exercise in the upright and recumbent position. Values are mean 1 SD. Legend: Œ, V CO2 in the upright position;, V CO2 in the recumbent position. *P<.05 between upright and recumbent position.

5 1028 CARDIOVASCULAR RESPONSES IN BICYCLE EXERCISE, Saitoh Fig 9. Change in V E during exercise in the upright and recumbent position. Values are mean 1 SD. Legend: Œ, V E in the upright position;, V E in the recumbent position. *P<.05 between upright and recumbent position. intensity in the present study. Because the backrest of the recumbent cycle ergometer we used was at an angle of 110, the venous return was probably less and more muscles were mobilized in the trunk and extremities as compared with other types of recumbent ergometers used in previous reports. 3,4 Furthermore, workloads of 50 and 70W seemed to be too light for healthy, young volunteers to use most muscles of the trunk and upper extremities in pedaling on an upright cycle ergometer. With regard to blood pressure, it is recognized that the elevation of blood pressure is strongly influenced by isometric handgripping to stabilize the body during exercise at submaximal intensity or higher when using a recumbent cycle ergometer. 14 Because we instructed all subjects not to hold seat grips strongly during the exercise, our study showed no significant differences in SBP and DBP between the upright and recumbent position at workloads of 50 and 70W. On the other hand, this study investigated the cardiovascular responses during low-intensity exercise, because there are only a few reports concerning the influence of the position when the exercise is performed at intensities of 15 and 30W. 7-10,16 Although no significant difference in heart rate was observed between the 2 positions, SBP, RPP, V O2, oxygen pulse, V CO2, and V E increased significantly in the recumbent position during exercise at 15 or 30W as compared with those during exercise in the upright position. When using a recumbent cycle ergometer, abdomen and hip muscles are mobilized to raise the legs up against the gravity and to assist pedaling even during lowintensity exercise. However, the weight of legs contributes to reduce the work of cycling in an upright cycle ergometer. It was supposed that greater V O2 was required in the recumbent position during exercise at an intensity of less than 30W, because most of the V O2 during low-intensity exercise originated from the active movement of legs. 11 The isometric contraction of abdominal muscles to raise the legs elevated blood pressure along with the increase of abdominal muscle pressure during low-intensity exercise using a recumbent cycle ergometer, as compared with an upright one. Furthermore, our study showed the striking changes in oxygen pulse and RPP, which indicate stroke volume and myocardial V O2, respectively; they were significantly higher in the recumbent position than the upright during low-intensity exercise, despite no significant difference in heart rate between the 2 positions. Our study also revealed that V CO2 and V E increased with the elevation of V O2, confirming the results of previous studies that showed they generally changed in parallel with V O2 during exercise below the anaerobic threshold. 16 It is well known that the recumbent cycle ergometer, which has a backrest to hold the body, is an excellent training equipment for patients physically impaired from muscle weakness, and orthopedic or neurologic problems, 17 and it is often used for patients with AMI whose heart rate, blood pressure, and electrocardiographic activity have to be fully monitored in phase I cardiac rehabilitation. 6 However, our study showed that a recumbent position induced more cardiovascular stress than an upright position during exercise, not at submaximal intensity or higher, but at low intensity. It is supposed that the cardiovascular stress observed at low-intensity exercise disturbs the hemodynamic stability more easily in aged patients than in young, healthy volunteers. Therefore, one should carefully monitor the cardiovascular responses in elderly and less fit patients, particularly those who have CAD, arrhythmia, and heart failure, even if they perform low-intensity exercise in a recumbent cycle ergometer. There are many patients who cannot carry out the submaximal exercise test in a clinical setting because of their cardiopulmonary, neurologic, or orthopedic limitations. The ACSM metabolic equation is used to estimate the V O2 to prescribe the training program for them, even if the workload is less than 50W. Assessing the suitability of the ACSM metabolic equation, our study showed that the estimated V O2 did not reflect the actual V O2 measured during exercise at 70W or less. The workload of the training program becomes relatively low and seems not to be enough even for patients with CAD, when it is prescribed according to the V O2 calculated by the ACSM metabolic equation, which is overestimated in comparison with the actual one. Limitation of the Study In our study, we did not measure cardiac output and arteriovenous oxygen difference invasively in the systemic circulation. When the change of V O2 was discussed on the difference of position during the exercise, not only the cardiac output and arteriovenous oxygen difference but also the blood flow and oxygen consumption in the muscle tissue should be accurately measured to clarify the difference in muscle activity used between upright and recumbent cycle ergometers. In addition, it is known that a disequilibrium of blood flow occurs and oxygen availability decreases in the muscles used for physical activity, when patients resume exercise training after prolonged bedrest. 18,19 The results of our study may differ from those obtained in patients with CAD who performed exercise according to the same study protocol. Because exercise training ameliorates the disequilibrium of blood flow to the muscles in patients with deconditioning, 20,21 the change of blood flow corresponding to the activity of muscles should be assessed in the future by using quantitative methods such as plethysmography or magnetic resonance imaging to compare cardiovascular responses between the upright and recumbent position. CONCLUSIONS Cardiovascular responses should be carefully monitored even during low-intensity exercise using a recumbent cycle ergometer, though it was a useful and safe device for the elderly or less-fit patients. The estimated V O2 using the ACSM metabolic equation did not reflect the actual V O2 during lowintensity exercise at 70W or less.

6 CARDIOVASCULAR RESPONSES IN BICYCLE EXERCISE, Saitoh 1029 References 1. American College of Sports Medicine. ACSM s guidelines for exercise testing and prescription. 6th ed. Philadelphia: Williams & Wilkins; Bonzheim SC, Franklin B, DeWitt C, et al. Physiologic response to recumbent versus upright cycle ergometry, implications for exercise prescription in patients with coronary arteries disease. Am J Cardiol 1992;69: Walsh-Riddle M, Blumenthal J. Cardiovascular responses during upright and semirecumbent cycle ergometry testing. Med Sci Sport Exerc 1989;21: Quinn T, Smith S, Vroman N, Kertzer R, Olney W. Physical responses of cardiac patients to supine, recumbent, and upright cycle ergometry. Arch Phys Med Rehabil 1995;76: Mcardle W, Katch F, Katch Y, editors. Exercise physiology. System of energy delivery and utilization: functional capacity of the cardiovascular system. 4th ed. Philadelphia: Williams & Wilkins; p Takahashi T, Tanabe K, Nakayama M, et al. [Cardiopulmonary response during supine and sitting bicycle exercise] [Japanese]. Jpn J Phys Fitness Med 1995;44: Matsunaga A, Masuda T, Ogura NM, et al. [Adaptation to a cycle ergometer exercise of patients with acute myocardial infarction undergoing phase I cardiac rehabilitation. Cardiovascular responses and autonomic nervous activities during low-intensity exercise] [Japanese]. J Jpn Assoc Cardiac Rehabil 2002;7: Matsunaga A, Masuda T, Ogura N, et al. Adaptation process to a low-intensity exercise with cycle ergometer by patients with acute myocardial infarction undergoing phase I cardiac rehabilitation. Circ J 2004;68: Taniguchi K, Itoh H, Yajima T, Doi M, Niwa A, Marumo F. Predischarge early exercise therapy in patients with acute myocardial infarction on the basis of anaerobic threshold (AT). Jpn Circ J 1990;54: Weissman C, Askanazi J, Rosenbaum S, Hyman A, Emili J, Kinney J. The effects of posture on the metabolic and ventilatory response to low level steady state exercise. Clin Sci 1986;71: Ellestad M. Cardiovascular and pulmonary responses to exercise. In: Ellestad M, Selvester R, Mishkin F, James F, editors. Stress testing. 5th ed. New York: Oxford Univ Pr; p Whipp B, Higgenbotham M, Cobb F. Estimating exercise stroke volume from asymptomatic oxygen pulse in humans. J Appl Physiol 1996;81: Wasserman K, Hansen J, Sue D, Whipp B, Casaburi R, editors. Exercise testing and interpretation. Philadelphia: Lea & Febiger; Cotsamire D, Sullivan M, Bashore T, Leier C. Position as a variable for cardiovascular responses during exercise. Clin Cardiol 1987;10: Proctor D, Sining W, Quinn T, et al. Submaximal responses to upright, recumbent and supine bicycle ergometer exercise [abstract]. Med Sci Sport Exerc 1990;22:S Takahashi T, Yamada S, Tanabe K, Izawa K, Itoh H, Murayama M. Cardiopulmonary responses at various angles of cycle backrest inclination. J Jpn Phys Ther Assoc 1999;2: American College of Sports Medicine. ACSM resource manual for the guidelines for exercise testing and prescription. 4th ed. Philadelphia: Williams & Wilkins; Greenleaf J. Energy and thermal regulation during bed rest and spaceflight. J Appl Physiol 1989;67: Bonde P, Suzuki Y, Kawakubo K, Gunji A. Effect of 20 days bed rest upon peripheral capillary filtration rate, venous compliance and blood flow in arms and legs. Acta Physiol Scand 1994; 616(Suppl): Drexler H, Depenbusch J, Truog A, Zelis R, Flaim S. Effects of diltiazem on cardiac function and regional blood flow at rest and during exercise in a conscious rat preparation of chronic heart failure. Circulation 1985;71: Drexler H. Reduced exercise tolerance in chronic heart failure and its relationship to neurohumoral factors. Eur Heart J 1991; 12(Suppl C):21-8 Suppliers a. AeroBike 75XL ME; Combi, Tokyo, Japan. b. Cordless Bike V60R; Senoh Corp, Tokyo, Japan. c. Bioview E; NEC San-ei Instruments, , Akebono-cho, Tachikawa-shi, Tokyo , Japan. d. STBP-780; Colin Medical Instruments, 5850 Farinon Dr, San Antonio, TX e. AT-1100; Anima, Tokyo, Japan. f. SPSS Inc, 233 S Wacker Dr, 11th Fl, Chicago, IL