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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

      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.

      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 (V̇o2) calculated by the American College of Sports Medicine (ACSM) metabolic equation reflects the actual V̇o2 at low-intensity 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), V̇o2, oxygen pulse, carbon dioxide output (V̇co2), and ventilatory equivalent (V̇e) were measured during graded exercise testing using upright and recumbent cycle ergometers. The estimated V̇o2 was calculated by using the ACSM metabolic equation.

      Results

      Systolic blood pressure, RPP, V̇o2, oxygen pulse, V̇co2, and V̇e 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 V̇o2 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 V̇o2 estimated using the ACSM metabolic equation did not reflect the actual V̇o2 during low-intensity exercise at 70W or less.

      Key words

      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 (V̇o2), as compared with a cycle ergometer.
      American College of Sports Medicine
      ACSM’s guidelines for exercise testing and prescription.
      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.
      American College of Sports Medicine
      ACSM’s guidelines for exercise testing and prescription.
      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
      • Bonzheim S.C.
      • Franklin B.
      • DeWitt C.
      • et al.
      Physiologic response to recumbent versus upright cycle ergometry, implications for exercise prescription in patients with coronary arteries disease.
      • Walsh-Riddle M.
      • Blumenthal J.
      Cardiovascular responses during upright and semirecumbent cycle ergometry testing.
      • Quinn T.
      • Smith S.
      • Vroman N.
      • Kertzer R.
      • Olney W.
      Physical responses of cardiac patients to supine, recumbent, and upright cycle ergometry.
      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).
      • Bonzheim S.C.
      • Franklin B.
      • DeWitt C.
      • et al.
      Physiologic response to recumbent versus upright cycle ergometry, implications for exercise prescription in patients with coronary arteries disease.
      • Walsh-Riddle M.
      • Blumenthal J.
      Cardiovascular responses during upright and semirecumbent cycle ergometry testing.
      • Quinn T.
      • Smith S.
      • Vroman N.
      • Kertzer R.
      • Olney W.
      Physical responses of cardiac patients to supine, recumbent, and upright cycle ergometry.
      It is generally recognized that heart rate and V̇o2 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.
      • Walsh-Riddle M.
      • Blumenthal J.
      Cardiovascular responses during upright and semirecumbent cycle ergometry testing.
      • Quinn T.
      • Smith S.
      • Vroman N.
      • Kertzer R.
      • Olney W.
      Physical responses of cardiac patients to supine, recumbent, and upright cycle ergometry.
      • Mcardle W.
      • Katch F.
      • Katch Y. editors
      Exercise physiology. System of energy delivery and utilization functional capacity of the cardiovascular system.
      • Takahashi T.
      • Tanabe K.
      • Nakayama M.
      • et al.
      [Cardiopulmonary response during supine and sitting bicycle exercise].
      Figure thumbnail gr1
      Fig 1(A) Upright cycle ergometer and (B) recumbent cycle ergometer.
      When a cardiac rehabilitation program advances from walking on the floor to exercising on cycle ergometers, a low-intensity 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.
      American College of Sports Medicine
      ACSM’s guidelines for exercise testing and prescription.
      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.
      • Matsunaga A.
      • Masuda T.
      • Ogura N.M.
      • 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].
      • 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.
      In addition, there are only a few detailed reports investigating cardiovascular responses during low-intensity exercise using a cycle ergometer, both in patients with CAD and in healthy, young volunteers.
      • Matsunaga A.
      • Masuda T.
      • Ogura N.M.
      • 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].
      • 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.
      • 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).
      • 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.
      On the other hand, the ACSM metabolic equation, which is widely used to prescribe a standard exercise training, estimates V̇o2 during exercise using a cycle ergometer and is reported to reflect precisely the actual V̇o2 measured at submaximal aerobic exercise at a load of more than 50W.
      American College of Sports Medicine
      ACSM’s guidelines for exercise testing and prescription.
      The ACSM metabolic equation is also applied when the workload is less than 50W, because it is convenient to assess the V̇o2 in patients who cannot perform the submaximal exercise test because of cardiopulmonary, neurologic, or orthopedic limitation.
      American College of Sports Medicine
      ACSM’s guidelines for exercise testing and prescription.
      However, it has not been established whether the ACSM metabolic equation is applicable to estimate the V̇o2 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 V̇o2 calculated by the ACSM metabolic equation reflects the actual V̇o2 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, 60.8±8.0kg), 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
      AeroBike 75XL ME; Combi, 111-0041 Tokyo, Japan.
      and a recumbent ergometer
      Cordless Bike V60R; Senoh Corp, 140-0004 Tokyo, Japan.
      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 maintained constant at 50rpm during the exercise test. Heart rate and electrocardiographic activity were continuously monitored by using an electrocardiography monitoring system,
      Bioview E; NEC San-ei Instruments, 1-25-12, Akebono-cho, Tachikawa-shi, Tokyo 190-8537, Japan.
      and SBP and diastolic blood pressure (DBP) were measured every 1 minute using an automatic manometer with the cuff method.
      STBP-780; Colin Medical Instruments, 5850 Farinon Dr, San Antonio, TX 78249.
      The V̇o2, carbon dioxide output (V̇co2), and ventilatory equivalent (V̇e) were measured breath by breath by using a gas analyzer
      AT-1100; Anima, 182-0034 Tokyo, Japan.
      throughout the test. The values of heart rate (HR), blood pressure, V̇o2, V̇co2, and V̇e 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 V̇o2
      • Ellestad M.
      Cardiovascular and pulmonary responses to exercise.
      and the oxygen pulse (oxygen pulse=V̇o2/HR) as stroke volume.
      • Whipp B.
      • Higgenbotham M.
      • Cobb F.
      Estimating exercise stroke volume from asymptomatic oxygen pulse in humans.
      • Wasserman K.
      • Hansen J.
      • Sue D.
      • Whipp B.
      • Casaburi R.
      Exercise testing and interpretation.

      The ACSM metabolic equation

      The V̇o2 estimated by using the ACSM metabolic equation consists of 3 parts in the case of exercise in a cycle ergometer: the V̇o2 used at the resting position on the seat and for unloaded cycling, and the V̇o2 that increases in proportion to the external workload. The V̇o2 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 V̇o2 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˙o2(mL·kg1·min1)=1.8(mL·kg1·m1)×work rate (kpm/min)/body weight (kg)+7.0
      (1)


      The estimated V̇o2 calculated by using the ACSM metabolic equation was compared with the actual V̇o2 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, V̇o2, oxygen pulse, V̇co2, and V̇e 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 V̇o2 among the 5 stages and between the actual and estimated V̇o2. If an F ratio was significant, the Tukey multiple range test was applied to find the significant differences between the actual and estimated V̇o2. 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,
      SPSS Inc, 233 S Wacker Dr, 11th Fl, Chicago, IL 60606.
      for Windows.

      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.
      Figure thumbnail gr3
      Fig 3Change in heart rate during exercise in the upright and recumbent position. Values are mean ±1 SD. Legend: ○, heart rate in the upright position; □, heart rate in the recumbent position. Abbreviation: HR, heart rate.
      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.
      Figure thumbnail gr4
      Fig 4Change in SBP and DBP during exercise in the upright and recumbent position. Values are mean ±1 SD. Legend: ○, blood pressure in the upright position; □, blood pressure in the recumbent position. *P<.05 between 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 thumbnail gr5
      Fig 5Change in RPP during the exercise in the upright and recumbent position. Values are mean ±1 SD. Legend: ○, RPP in the upright position; □, RPP in the recumbent position. *P<.05 between upright and recumbent position.
      Figure 6 shows the actual V̇o2 measured during exercise in the upright and recumbent cycle ergometers and the estimated V̇o2 calculated by using the ACSM metabolic equation. Although the actual V̇o2 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 V̇o2 was significantly higher at every workload than the actual V̇o2 measured during the exercise either in the upright or recumbent cycle ergometer (all P<.05).
      Figure thumbnail gr6
      Fig 6Change in V̇o2 during exercise in the upright and recumbent position. Values are mean ±1 SD. Legend: ○, V̇o2 in the upright position; □, V̇o2 in the recumbent position; Δ, estimated V̇o2 calculated by using the ACSM metabolic equation. *P<.05 between upright and recumbent position. †P<.05 between the V̇o2 measured in the upright position and the estimated V̇o2. ‡P<.05 between the V̇o2 measured in the recumbent position and the estimated V̇o2.
      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 position, those at 15 and 30W were significantly higher in the recumbent position (both P<.05).
      Figure thumbnail gr7
      Fig 7Change in oxygen pulse during exercise in the upright and recumbent position. Values are mean ±1 SD. Legend: ○, oxygen pulse in the upright position; □, oxygen pulse in the recumbent position. Abbreviation: O2 pulse, oxygen pulse. *P<.05 between upright and recumbent position.
      The V̇co2 at each workload is shown in figure 8. Although there were no significant differences in the V̇co2 at rest, 50W, and 70W between the 2 positions, the V̇co2 at 15 or 30W was significantly higher in the recumbent position than in the upright one (both P<.05).
      Figure thumbnail gr8
      Fig 8Change in V̇co2 during exercise in the upright and recumbent position. Values are mean ±1 SD. Legend: ○, V̇co2 in the upright position; □, V̇co2 in the recumbent position. *P<.05 between upright and recumbent position.
      The V̇e at each workload is shown in figure 9. Although there were no significant differences in the V̇e at rest, 30W, 50W, and 70W between the 2 positions, the V̇e at 15W was significantly higher in the recumbent position than in the upright one (P<.05).
      Figure thumbnail gr9
      Fig 9Change in V̇e during exercise in the upright and recumbent position. Values are mean ±1 SD. Legend: ○, V̇e in the upright position; □, V̇e in the recumbent position. *P<.05 between upright and recumbent position.

      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.
      • Bonzheim S.C.
      • Franklin B.
      • DeWitt C.
      • et al.
      Physiologic response to recumbent versus upright cycle ergometry, implications for exercise prescription in patients with coronary arteries disease.
      • Walsh-Riddle M.
      • Blumenthal J.
      Cardiovascular responses during upright and semirecumbent cycle ergometry testing.
      • Quinn T.
      • Smith S.
      • Vroman N.
      • Kertzer R.
      • Olney W.
      Physical responses of cardiac patients to supine, recumbent, and upright cycle ergometry.
      • Cotsamire D.
      • Sullivan M.
      • Bashore T.
      • Leier C.
      Position as a variable for cardiovascular responses during exercise.
      • Proctor D.
      • Sining W.
      • Quinn T.
      • et al.
      Submaximal responses to upright, recumbent and supine bicycle ergometer exercise [abstract].
      Consequently, it has been pointed out that heart rate, RPP, and V̇o2 are lower and oxygen pulse is higher in the recumbent position than in the upright one during exercise at submaximal intensity.
      • Bonzheim S.C.
      • Franklin B.
      • DeWitt C.
      • et al.
      Physiologic response to recumbent versus upright cycle ergometry, implications for exercise prescription in patients with coronary arteries disease.
      • Walsh-Riddle M.
      • Blumenthal J.
      Cardiovascular responses during upright and semirecumbent cycle ergometry testing.
      • Quinn T.
      • Smith S.
      • Vroman N.
      • Kertzer R.
      • Olney W.
      Physical responses of cardiac patients to supine, recumbent, and upright cycle ergometry.
      • Cotsamire D.
      • Sullivan M.
      • Bashore T.
      • Leier C.
      Position as a variable for cardiovascular responses during exercise.
      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.
      • Walsh-Riddle M.
      • Blumenthal J.
      Cardiovascular responses during upright and semirecumbent cycle ergometry testing.
      • Quinn T.
      • Smith S.
      • Vroman N.
      • Kertzer R.
      • Olney W.
      Physical responses of cardiac patients to supine, recumbent, and upright cycle ergometry.
      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.
      • Walsh-Riddle M.
      • Blumenthal J.
      Cardiovascular responses during upright and semirecumbent cycle ergometry testing.
      Therefore, the V̇o2 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, V̇o2, or oxygen pulse between the upright and recumbent position during exercise at submaximal 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.
      • Walsh-Riddle M.
      • Blumenthal J.
      Cardiovascular responses during upright and semirecumbent cycle ergometry testing.
      • Quinn T.
      • Smith S.
      • Vroman N.
      • Kertzer R.
      • Olney W.
      Physical responses of cardiac patients to supine, recumbent, and upright cycle ergometry.
      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.
      • Cotsamire D.
      • Sullivan M.
      • Bashore T.
      • Leier C.
      Position as a variable for cardiovascular responses during exercise.
      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.
      • Matsunaga A.
      • Masuda T.
      • Ogura N.M.
      • 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].
      • 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.
      • 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).
      • 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.
      • Takahashi T.
      • Yamada S.
      • Tanabe K.
      • Izawa K.
      • Itoh H.
      • Murayama M.
      Cardiopulmonary responses at various angles of cycle backrest inclination.
      Although no significant difference in heart rate was observed between the 2 positions, SBP, RPP, V̇o2, oxygen pulse, V̇co2, and V̇e 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 low-intensity exercise. However, the weight of legs contributes to reduce the work of cycling in an upright cycle ergometer. It was supposed that greater V̇o2 was required in the recumbent position during exercise at an intensity of less than 30W, because most of the V̇o2 during low-intensity exercise originated from the active movement of legs.
      • Ellestad M.
      Cardiovascular and pulmonary responses to exercise.
      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 V̇o2, 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 V̇co2 and V̇e increased with the elevation of V̇o2, confirming the results of previous studies that showed they generally changed in parallel with V̇o2 during exercise below the anaerobic threshold.
      • Takahashi T.
      • Yamada S.
      • Tanabe K.
      • Izawa K.
      • Itoh H.
      • Murayama M.
      Cardiopulmonary responses at various angles of cycle backrest inclination.
      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,
      American College of Sports Medicine. ACSM resource manual for the guidelines for exercise testing and prescription.
      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.
      • Takahashi T.
      • Tanabe K.
      • Nakayama M.
      • et al.
      [Cardiopulmonary response during supine and sitting bicycle exercise].
      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 V̇o2 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 V̇o2 did not reflect the actual V̇o2 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 V̇o2 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 V̇o2 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.
      • Greenleaf J.
      Energy and thermal regulation during bed rest and spaceflight.
      • 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.
      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,
      • 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.
      • Drexler H.
      Reduced exercise tolerance in chronic heart failure and its relationship to neurohumoral factors.
      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 V̇o2 using the ACSM metabolic equation did not reflect the actual V̇o2 during low-intensity exercise at 70W or less.
      Suppliers
      aAeroBike 75XL ME; Combi, 111-0041 Tokyo, Japan.
      bCordless Bike V60R; Senoh Corp, 140-0004 Tokyo, Japan.
      cBioview E; NEC San-ei Instruments, 1-25-12, Akebono-cho, Tachikawa-shi, Tokyo 190-8537, Japan.
      dSTBP-780; Colin Medical Instruments, 5850 Farinon Dr, San Antonio, TX 78249.
      eAT-1100; Anima, 182-0034 Tokyo, Japan.
      fSPSS Inc, 233 S Wacker Dr, 11th Fl, Chicago, IL 60606.

      References

        • American College of Sports Medicine
        ACSM’s guidelines for exercise testing and prescription.
        6th ed. Williams & Wilkins, Philadelphia2000
        • Bonzheim S.C.
        • 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: 40-44
        • Walsh-Riddle M.
        • Blumenthal J.
        Cardiovascular responses during upright and semirecumbent cycle ergometry testing.
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