- Email: [email protected]
Physiological responses to high intensity, constant-load arm exercise in COPD
ARTICLE IN PRESS Respiratory Medicine (2008) 102, 348–353
Physiological responses to high intensity, constant-load arm exercise in COPD Zoe J. McKeougha,, Jennifer A. Alisona, Bradley A. Speersb, Peter T.P. Byeb a
Discipline of Physiotherapy, Faculty of Health Sciences, Sydney University, P.O. Box 170, Lidcombe, NSW 2141, Australia Department of Respiratory Medicine, Royal Prince Alfred Hospital, Missenden Rd, Camperdown, NSW 2050, Australia
b
Received 4 June 2007; accepted 31 October 2007 Available online 11 December 2007
KEYWORDS Chronic obstructive pulmonary disease; Exercise; Dyspnoea; Exercise test
Summary The aim of the study was to compare the metabolic, ventilatory and dyspnoea responses of a single bout of high intensity, constant-load arm exercise to peak arm exercise in people with chronic obstructive pulmonary disease (COPD). Thirty people with COPD (mean age7SD ¼ 6578 years; FEV1% predicted ¼ 56712%) were included. All subjects performed an incremental arm exercise test to peak work capacity on an arm ergometer and, on a separate day, a constant-load arm exercise test at 80% of the peak work rate achieved on the incremental test. Throughout both exercise tests, oxygen consumption (VO2), minute ventilation (VE), dyspnoea and rate of perceived exertion (RPE) were measured each minute. Peak work rate on the incremental test was 33.0710.1 W with a mean duration of 6.672.0 min. The mean duration of the constant-load test of 7.172.9 min was not significantly different to the incremental test (p ¼ 0.3). At end exercise, VE, dyspnoea and RPE for the constant-load test was significantly higher compared to the incremental test (VE: 41.3714.4 L/min and 38.3711.8 L/min; dyspnoea: 5.672.7 and 4.672.1; RPE: 7.172.3 and 6.072.0; all po0.05). Constant-load arm exercise at 80% peak work rate elicits higher ventilatory, dyspnoea and RPE responses at end exercise compared to incremental arm exercise in people with COPD. This finding suggests that an intensity of 80% peak work rate may be too high as an initial training intensity for supported arm exercise in people with COPD. & 2007 Elsevier Ltd. All rights reserved.
Introduction
Corresponding author. Tel.: +61 2 9351 9269;
fax: +61 2 9351 9278. E-mail address: [email protected] (Z.J. McKeough). 0954-6111/$ - see front matter & 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.rmed.2007.10.020
People with chronic obstructive pulmonary disease (COPD) have a reduced arm exercise capacity1 and, as a result, are encouraged to perform arm training in pulmonary rehabilitation. While a number of studies have indicated the effectiveness of arm training to improve supported and
ARTICLE IN PRESS Arm exercise in COPD unsupported arm exercise capacity,2–5 the intensity of arm training has either varied significantly or been inadequately described. In contrast, intensity of leg training is well described with studies indicating that a moderate to high intensity of leg cycle training produces the greatest physiological benefit.6,7 One recent study of supported arm training in subjects with COPD utilised a high intensity arm training protocol (80% peak work rate) but no information was provided on how the subjects responded during a session of this training.8 Furthermore, we are not aware of any other study which has compared the physiological responses of a single bout of high intensity, constant-load, supported, arm exercise with incremental, supported arm exercise to peak work capacity in people with COPD. An understanding of this relationship will be important to determine whether prescription of high intensity supported arm training is feasible at the start of a pulmonary rehabilitation program. The aim of this study was to compare the metabolic, ventilatory and dyspnoea responses of a single bout of high intensity, constant-load, supported arm exercise with those of incremental, supported arm exercise to peak work capacity in subjects with COPD. The hypothesis was that the metabolic, ventilatory and dyspnoea responses at end exercise would be lower in the high intensity, constant-load exercise than the responses at end exercise in incremental arm exercise.
Methods Subjects Thirty subjects, diagnosed with COPD, were recruited from the Department of Respiratory Medicine, Royal Prince Alfred Hospital, Australia. All subjects were stable on entry to the study, had no shoulder problems and had never participated in a pulmonary rehabilitation program. Informed, written consent was obtained from all subjects, and the study was approved by the Sydney South West Area Health Service (Eastern Zone).
Measurements Respiratory function tests Measurements of spirometry (Sensormedics Vmax 20; Sensormedics Corporation, CA) and lung volumes (Sensormedics V6200 Autobox Body Plethysmograph; Sensormedics Corporation, CA) were performed and compared to predicted normal values for spirometry9 and lung volumes.10 Bronchodilators, where prescribed, were given prior to lung function measurements.
349 replaced with handles). For both tests, subjects were seated and the arm crank height was adjusted so that the fulcrum of the pedals was at the level of the gleno-humeral joint. During the incremental test, workloads were increased by 5 W every minute until the subjects indicated that they could not continue. The work rate for the constant-load test was set at 80% of the peak work rate attained during the incremental test. During both exercise tests, the subjects exercised at 50–60 rpm and breathed through a calibrated mass flow sensor with expired gas sampled on a breath-by-breath basis (Vmax 29 Cardiopulmonary Exercise Testing Instrument; Sensormedics Corporation, California, USA) so that oxygen consumption (VO2), carbon dioxide production (VCO2), minute ventilation (VE), tidal volume (VT) and breathing frequency (Fb) could be determined. Maximal voluntary ventilation (MVV) was determined by multiplying the FEV1 by 3511 so that VE/MVV could be determined. End-expiratory lung volume (EELV) was also measured during both tests by instructing the subject to perform inspiratory capacity manoeuvres at rest and in the final 3 s of each minute of exercise. At least three breaths prior to the manoeuvres were monitored to ensure stability of each subject’s end expiratory lung volume. This methodology has been described previously during leg exercise and supported arm exercise,12 and has been shown to be reliable and reproducible in COPD subjects.13,14 Heart rate (HR) and pulse oxygen saturation (SpO2%) were obtained with a forehead probe attached to a pulse oximeter (N200: Nellcor, Hayward CA). Subjects scored their dyspnoea and rate of perceived exertion (RPE) on a modified Borg scale reading 0 (‘‘nothing at all’’) to 10 (‘‘maximal’’).15,16 Subjects were also asked to comment on whether exercise was terminated due to dyspnoea, arm fatigue or a combination of both.
Statistical analysis The StatView statistical package was used for analysis (Version 4.57 1992–1996, Abacus Concepts Inc., California). Statistical guidelines were provided by Altman.17 All data are presented as mean7SD. The mean difference with the 95% confidence interval (CI) is included where appropriate. The measurements taken during both exercise tests were compared using a paired t-test. Significance was set at po0.05.
Results Mean anthropometric data and lung function results for the 30 COPD subjects are presented in Table 1.
Responses at the end of exercise Exercise tests All subjects performed a symptom-limited, incremental, supported arm exercise test to peak work capacity and, on a separate day, performed a symptom-limited, constant-load, supported arm exercise test which represented a single-bout of endurance arm exercise training. The arm exercise tests utilised an electrically braked bicycle ergometer (SeimensElma; Solina, Sweden), modified for arm work (i.e. the gear system was mounted on an adjustable table and pedals were
The metabolic and ventilatory responses in the COPD subjects can be found in Table 2. There was no significant difference in the duration of the incremental test and the constant-load test. The work rate performed during the constant-load test averaged 6 W less than that performed during the incremental test. Despite this, there was a significantly higher VE, VE/MVV, VT, dyspnoea and RPE for the constant-load test compared to the incremental test at end
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exercise. The predominant symptom reported by subjects as the reason for stopping exercise during both the incremental test and constant-load test is given in Figure 1. Of the 15 subjects who reported arm fatigue as the reason for terminating incremental arm exercise, nine of these subjects also reported arm fatigue as the reason for terminating the constant-load test while the remaining six subjects complained of both arm fatigue and dyspnoea at the end of the constant-load test.
Table 1 data.
Baseline anthropometric and lung function
Baseline (mean7SD) Age (yr) BMI (kg/m2) FEV1 (L) % pred FVC (L) % pred TLC (L) % pred FRC (L) % pred RV (L) % pred
6578 26.375.4 1.570.4 56712 3.070.7 78713 6.771.3 117717 4.471.2 134729 3.771.1 170748
Definition of abbreviations: BMI:body mass index, FEV1: forced expiratory volume in one second, FVC:forced vital capacity, TLC:total lung capacity, FRC:functional residual capacity, RV:residual volume, yr:year, kg/m2:kilograms per metre, L:litre, % pred:percentage of predicted.
Responses throughout exercise The metabolic and ventilatory responses during the incremental test and constant-load test in a representative subject with COPD are shown in Figures 2 and 3, respectively. This subject’s responses corresponded to the pattern of exercise response seen by the group. There was a linear increase in both VO2 and VE with increasing work rate while the relationship of both VO2 and VE to time during constant work rate exercise tended to be curvilinear. VO2 started to plateau towards the end of the constant-load test. There was a curvilinear relationship of dyspnoea and RPE to work rate and dyspnoea and RPE to time. This pattern indicated that larger increases in dyspnoea and RPE occurred towards the end of exercise for a given change in work rate or time.
Both n = 11
Arm Fatigue n = 15
Dyspnea n=4
Both n = 13
Arm Fatigue n = 15
Dyspnea n=2
Figure 1 The number of subjects terminating arm exercise due to either arm fatigue, dyspnoea or both arm fatigue and dyspnoea in the (A) incremental arm exercise test and the (B) constant-load arm exercise test.
Table 2 End-exercise responses to incremental and constant-load arm exercise (including the mean difference between the parameters measured).
Work rate (W) (% of incremental) Duration (min) VO2 (L/min) VO2 (ml/kg/min) VCO2 (L/min) VE (L/min) VE/MVV VT (L) Fb (brths/min) SpO2 (%) HR (bpm) Dyspnoea RPE Change in EELV (L)
Incremental (mean7SD)
Constant-load (mean7SD)
Mean diff (95% CI)
33.0710.1
26.879.1 (80.975.6) 7.172.9 0.8370.2 11.173.0 0.9470.3 41.3714.4 80719 1.1870.3 3578 9673 109723 5.672.7 7.172.3 0.570.3
6 (5 to 7)
6.672.0 0.8270.2 11.073.0 0.9170.3 38.3711.8 73717 1.1270.3 3578 9873 109718 4.672.1 6.072.0 0.570.3
0.5 (0.5 to 1.5) 0.01 (0.3 to 0.5) 0.1 (0.3 to 0.6) 0.03 (0.02 to 0.1) 3 (0.9 to 5) 7 (3 to 11) 0.1 (0.001 to 0.1) 0.4 (0.8 to 1.6) 1.2 (2.3 to 0.01) 0.7 (6 to 8) 1 (0.1 to 2) 1 (0.5 to 2) 0.04 (0.1 to 0.04)
Definition of abbreviations: VO2:oxygen consumption, VCO2:carbon dioxide production, VE:minute ventilation, VE/MVV:ratio of minute ventilation to maximal voluntary ventilation, VT:tidal volume, Fb:breathing frequency, SpO2:pulse oxygen saturation, HR:heart rate, RPE:rate of perceived exertion, EELV:end-expiratory lung volume, min:minute, L/min:litres per minute, ml/kg/min:millilitres per kilogram per minute, L:litres, brths/min:breaths per minute, %:percentage, bpm:beats per minute. Significant difference between tests (po0.05).
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Figure 2 The physiological responses during the incremental arm exercise test in one representative subject (Subject 25) with COPD. (A) VO2, (B) VE, (C) dyspnoea and (D) RPE. (Abbreviations: VO2:oxygen consumption, VE:minute ventilation, RPE:rate of perceived exertion).
Discussion This study is the first to compare the physiological responses of a single bout of constant-load, supported arm exercise at an intensity of 80% peak work rate compared to incremental, supported arm exercise to peak work rate in people with COPD. The main findings were that the ventilatory, dyspnoea and arm fatigue responses at end exercise during the constant-load arm exercise were significantly higher than those at the end of the incremental arm exercise. In addition, more people with COPD indicated that arm fatigue or a combination of arm fatigue and dyspnoea limited exercise during both types of tests rather than dyspnoea alone. These results have implications for the initial prescription of arm training intensity for people with COPD. This study highlighted that the major limitation to arm exercise in this group of subjects with COPD was at the peripheral muscle level rather than due to ventilatory factors. The evidence for this comes from the fact that, at a similar VO2 for incremental and constant-load arm exercise, there was adequate breathing reserve (i.e. VE/MVVo80%) and more subjects terminated both forms of arm exercise because of arm fatigue rather than dyspnoea. As arm exercise is performed by a relatively small muscle mass compared to leg exercise, the peak ventilatory requirements of arm exercise in healthy subjects are low compared to leg exercise.18 Thus, in COPD subjects with only moderate lung impairment (FEV1 ¼ 56% predicted), the ventilation
required for arm exercise will not be high compared to the maximum ventilatory capacity such that arm fatigue could occur prior to ventilatory factors limiting exercise. Muscle fatigue has also been shown to be a factor limiting constant work rate leg exercise in COPD subjects. One study examined quadriceps muscle fatigue using twitch force measures following constant work rate leg exercise and demonstrated the existence of quadriceps muscle fatigue in 50% of the COPD subjects.19 Some studies have interpreted constant-load exercise tests based on critical power-duration considerations.20,21 While the measurement of critical power was beyond the scope of this paper, these studies are useful in understanding why the COPD subjects in the present study were unable to tolerate a work rate of 80% peak arm work rate. Critical power refers to the highest work rate, which can be sustained without exhaustion. Critical power for leg exercise in COPD subjects occurs at a lower absolute work rate than in healthy subjects but when represented as a percentage of peak work rate, it has been shown to be approximately 82% in COPD subjects and 68% in healthy subjects.21 These results indicate that COPD subjects can sustain higher relative leg work rates for training than healthy subjects.22 The fact that subjects in the present study were unable to sustain arm exercise at 80% peak work rate without exhaustion suggests that, for the arms of subjects with COPD, critical power (as a percentage of peak work rate) would be less than 80%. As the arm muscles in COPD subjects
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Figure 3 The physiological responses during the constant-load arm exercise test at 30 W in one representative subject (Subject 25) with COPD. (A) VO2, (B) VE (C) dyspnoea and (D) RPE. (Abbreviations: VO2:oxygen consumption, VE:minute ventilation, RPE:rate of perceived exertion).
have been shown to be well preserved,23 it could be argued that a relatively higher peak work rate for the arms could be achieved such that the critical power for arms now represents a lower fraction of the peak work rate (i.e. a response pattern for the arm muscles in COPD subjects similar to the critical power response seen in the leg muscles of healthy subjects). The only other studies which have examined both incremental arm exercise and endurance arm exercise at a constant work rate in people with COPD have used a moderate intensity for the constant work rate (i.e. p50% peak work rate).4,24 No statistical comparison of the responses was made between the two types of exercise in these studies. Despite this, on further review of the data, the physiological responses were higher at the end of the incremental exercise than at the end of the constant-load exercise. Working at a higher percent of peak work rate (i.e. 80% peak work rate) during constant-load exercise, as in our study, is likely to be above the critical power compared to working at a moderate percent of peak work capacity. This could explain the higher ventilation during constant-load exercise compared to incremental exercise (Figure 3B). Although more subjects stopped arm exercise because of symptoms of arm fatigue, dyspnoea scores were still high at end exercise for both forms of arm exercise. Our group has previously shown high dyspnoea scores at the end of incremental arm exercise which were not significantly different to those of leg exercise.12 The mechanism for the increase in dyspnoea scores during exercise has been studied previously with acute dynamic hyperinflation play-
ing a major role.13 The present study measured the EELV at end exercise during incremental and constant-load arm exercise and showed an increase in mean EELV of 0.5 L for both types of arm exercise. It is likely that this degree of dynamic hyperinflation was a contributing factor to the dyspnoea scores reported in the current study. The clinical implications of this study are significant. It is clear from the results that an initial high intensity arm training program for the length of time prescribed for aerobic benefits (i.e. approx.15 min) would not be possible as subjects were only able to exercise for a mean of 7 min.5 If attempted, subjects are unlikely to comply with training due to the high levels of perceived exertion and dyspnoea which would be experienced. Future research should examine whether high intensity interval training for the arms, in which bouts of high intensity exercise are interspersed with periods of rest or low intensity exercise, could be better tolerated. This study was limited to evaluating the physiological responses to supported arm exercise. As unsupported arm exercise is recognised as more representative of functional daily arm tasks than supported arm exercise for people with COPD, further studies are required to evaluate the ability of people with COPD to perform high intensity unsupported arm training. In conclusion, the results of the current study indicate significantly greater ventilatory, dyspnoea and arm fatigue responses at the end of exercise during high intensity, constant-load arm exercise compared to incremental arm exercise in people with COPD. This suggests that supported
ARTICLE IN PRESS Arm exercise in COPD arm training at an intensity of 80% peak work rate may be too high as an initial exercise prescription for people with COPD.
Funding This study was supported by the Australian Respiratory Council. This funding source was not involved in any aspect of study design or interpretation.
Conflict of interest The authors wish to declare no competing interests with respect to this work.
Acknowledgements The authors would like to thank Lissa Spencer for assistance in subject recruitment and the staff of the Respiratory Medicine Department at Royal Prince Alfred Hospital for the use of the lung function and exercise laboratory.
References 1. Celli BR, Rassulo J, Make BJ. Dyssynchronous breathing during arm but not leg exercise in patients with chronic airflow obstruction. N Engl J Med 1986;314:1485–90. 2. Ries AL, Ellis B, Hawkins RW. Upper extremity exercise training in chronic obstructive pulmonary disease. Chest 1988;93:688–92. 3. Couser JI, Martinez FJ, Celli BR. Pulmonary rehabilitation that includes arm exercise reduces metabolic and ventilatory requirements for simple arm elevation. Chest 1993;103:37–41. 4. Lake FR, Henderson K, Briffa T, Openshaw J, Musk AW. Upperlimb and lower-limb exercise training in patients with chronic airflow limitation. Chest 1990;97:1077–82. 5. Martinez FJ, Vogel PD, Dupont DN, Stanopoulos I, Gray A, Beamis JF. Supported arm exercise versus unsupported arm exercise in the rehabilitation of patients with severe chronic airflow obstruction. Chest 1993;103:1397–402. 6. Casaburi R, Vatessio A, Iolif F, Zanaboni S, Donner CF, Wasserman K. Reductions in exercise lactic acidosis and ventilation as a result of exercise training in patients with obstructive lung disease. Am Rev Respir Dis 1991;143:9–18. 7. Maltais F, LeBlanc P, Jobin J, et al. Intensity of training and physiologic adaptation in patients with chronic obstructive pulmonary disease. Am J Respir Crit Care Med 1997;155: 555–61. 8. Gigliotti F, Coli C, Bianchi R, et al. Arm exercise and hyperinflation in patients with COPD. Chest 2005;128:1225–32.
353 9. Crapo RO, Morris AH, Gardner RM. Reference spirometric values using techniques and equipment that meet ATS recommendations. Am Rev Respir Dis 1981;123:659–64. 10. Goldman HI, Becklake MR. Respiratory function tests. Normal values at median altitudes and the prediction of normal results. Am Rev Tuberc 1959;79:457–67. 11. Clark TJH, Freedman S, Campbell EJM, Winn RR. The ventilatory capacity of patients with chronic airways obstruction. Clin Sci 1969;36:307–16. 12. McKeough ZJ, Alison JA, Bye PT. Arm exercise capacity and dyspnea ratings in subjects with chronic obstructive pulmonary disease. J Cardiopulm Rehabil 2003;23:218–25. 13. O’Donnell DE, Webb K. Exertional breathlessness in patients with chronic airflow limitation: the role of lung hyperinflation. Am Rev Respir Dis 1993;148:1351–7. 14. Yan S, Kaminski D, Sliwinski P. Reliability of inspiratory capacity for estimating end-expiratory lung volume changes during exercise in patients with chronic obstructive pulmonary disease. Am J Respir Crit Care Med 1997;156:55–9. 15. Borg G. Perceived exertion as an indicator of somatic stress. Scand J Rehabil Med 1970;2:92–8. 16. Burdon JG, Juniper EF, Killian KJ, Hargreave FE, Campbell EJ. The perception of breathlessness in asthma. Am Rev Respir Dis 1982;126:825–8. 17. Altman D. Practical statistics for medical research. London: Chapman & Hall; 1991. 18. Alison JA, Regnis JA, Donnelly PM, Adams RD, Sullivan CE, Bye PTP. End-expiratory lung volume during arm and leg exercise in normal subjects and patients with cystic fibrosis. Am J Respir Crit Care Med 1998;158:1450–8. 19. Saey D, Debigare R, LeBlanc P, et al. Contractile leg fatigue after cycle exercise: a factor limiting exercise in patients with chronic obstructive pulmonary disease. Am J Respir Crit Care Med 2003;168:425–30. 20. Casaburi R. Factors determining constant work rate exercise tolerance in COPD and their role in dictating the minimal clinically important difference in response to interventions. J Chronic Obstructive Pulm Dis 2005;2:131–6. 21. Neder JA, Jones PW, Nery LE, Whipp BJ. Determinants of the exercise endurance capacity in patients with chronic obstructive pulmonary disease: the power–duration relationship. Am J Respir Crit Care Med 2000;162:497–504. 22. Punzal PA, Ries AL, Kaplan RM, Prewitt LM. Maximum intensity exercise training in patients with chronic obstructive pulmonary disease. Chest 1991;100:618–23. 23. Gea JG, Pasto M, Carmona MA, Orozco-Levi M, Palomeque J, Broquetas J. Metabolic characteristics of the deltoid muscle in patients with chronic obstructive pulmonary disease. Eur Respir J 2001;17:939–45. 24. Franssen FME, Wouters EFM, Baarends EM, Akkermans MA, Schols AMWJ. Arm mechanical efficiency and arm exercise capacity are relatively preserved in chronic obstructive pulmonary disease. Med Sci Sports Exercise 2002;34:1570–6.
Physiological responses to high intensity, constant-load arm exercise in COPD Zoe J. McKeougha,, Jennifer A. Alisona, Bradley A. Speersb, Peter T.P. Byeb a
Discipline of Physiotherapy, Faculty of Health Sciences, Sydney University, P.O. Box 170, Lidcombe, NSW 2141, Australia Department of Respiratory Medicine, Royal Prince Alfred Hospital, Missenden Rd, Camperdown, NSW 2050, Australia
b
Received 4 June 2007; accepted 31 October 2007 Available online 11 December 2007
KEYWORDS Chronic obstructive pulmonary disease; Exercise; Dyspnoea; Exercise test
Summary The aim of the study was to compare the metabolic, ventilatory and dyspnoea responses of a single bout of high intensity, constant-load arm exercise to peak arm exercise in people with chronic obstructive pulmonary disease (COPD). Thirty people with COPD (mean age7SD ¼ 6578 years; FEV1% predicted ¼ 56712%) were included. All subjects performed an incremental arm exercise test to peak work capacity on an arm ergometer and, on a separate day, a constant-load arm exercise test at 80% of the peak work rate achieved on the incremental test. Throughout both exercise tests, oxygen consumption (VO2), minute ventilation (VE), dyspnoea and rate of perceived exertion (RPE) were measured each minute. Peak work rate on the incremental test was 33.0710.1 W with a mean duration of 6.672.0 min. The mean duration of the constant-load test of 7.172.9 min was not significantly different to the incremental test (p ¼ 0.3). At end exercise, VE, dyspnoea and RPE for the constant-load test was significantly higher compared to the incremental test (VE: 41.3714.4 L/min and 38.3711.8 L/min; dyspnoea: 5.672.7 and 4.672.1; RPE: 7.172.3 and 6.072.0; all po0.05). Constant-load arm exercise at 80% peak work rate elicits higher ventilatory, dyspnoea and RPE responses at end exercise compared to incremental arm exercise in people with COPD. This finding suggests that an intensity of 80% peak work rate may be too high as an initial training intensity for supported arm exercise in people with COPD. & 2007 Elsevier Ltd. All rights reserved.
Introduction
Corresponding author. Tel.: +61 2 9351 9269;
fax: +61 2 9351 9278. E-mail address: [email protected] (Z.J. McKeough). 0954-6111/$ - see front matter & 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.rmed.2007.10.020
People with chronic obstructive pulmonary disease (COPD) have a reduced arm exercise capacity1 and, as a result, are encouraged to perform arm training in pulmonary rehabilitation. While a number of studies have indicated the effectiveness of arm training to improve supported and
ARTICLE IN PRESS Arm exercise in COPD unsupported arm exercise capacity,2–5 the intensity of arm training has either varied significantly or been inadequately described. In contrast, intensity of leg training is well described with studies indicating that a moderate to high intensity of leg cycle training produces the greatest physiological benefit.6,7 One recent study of supported arm training in subjects with COPD utilised a high intensity arm training protocol (80% peak work rate) but no information was provided on how the subjects responded during a session of this training.8 Furthermore, we are not aware of any other study which has compared the physiological responses of a single bout of high intensity, constant-load, supported, arm exercise with incremental, supported arm exercise to peak work capacity in people with COPD. An understanding of this relationship will be important to determine whether prescription of high intensity supported arm training is feasible at the start of a pulmonary rehabilitation program. The aim of this study was to compare the metabolic, ventilatory and dyspnoea responses of a single bout of high intensity, constant-load, supported arm exercise with those of incremental, supported arm exercise to peak work capacity in subjects with COPD. The hypothesis was that the metabolic, ventilatory and dyspnoea responses at end exercise would be lower in the high intensity, constant-load exercise than the responses at end exercise in incremental arm exercise.
Methods Subjects Thirty subjects, diagnosed with COPD, were recruited from the Department of Respiratory Medicine, Royal Prince Alfred Hospital, Australia. All subjects were stable on entry to the study, had no shoulder problems and had never participated in a pulmonary rehabilitation program. Informed, written consent was obtained from all subjects, and the study was approved by the Sydney South West Area Health Service (Eastern Zone).
Measurements Respiratory function tests Measurements of spirometry (Sensormedics Vmax 20; Sensormedics Corporation, CA) and lung volumes (Sensormedics V6200 Autobox Body Plethysmograph; Sensormedics Corporation, CA) were performed and compared to predicted normal values for spirometry9 and lung volumes.10 Bronchodilators, where prescribed, were given prior to lung function measurements.
349 replaced with handles). For both tests, subjects were seated and the arm crank height was adjusted so that the fulcrum of the pedals was at the level of the gleno-humeral joint. During the incremental test, workloads were increased by 5 W every minute until the subjects indicated that they could not continue. The work rate for the constant-load test was set at 80% of the peak work rate attained during the incremental test. During both exercise tests, the subjects exercised at 50–60 rpm and breathed through a calibrated mass flow sensor with expired gas sampled on a breath-by-breath basis (Vmax 29 Cardiopulmonary Exercise Testing Instrument; Sensormedics Corporation, California, USA) so that oxygen consumption (VO2), carbon dioxide production (VCO2), minute ventilation (VE), tidal volume (VT) and breathing frequency (Fb) could be determined. Maximal voluntary ventilation (MVV) was determined by multiplying the FEV1 by 3511 so that VE/MVV could be determined. End-expiratory lung volume (EELV) was also measured during both tests by instructing the subject to perform inspiratory capacity manoeuvres at rest and in the final 3 s of each minute of exercise. At least three breaths prior to the manoeuvres were monitored to ensure stability of each subject’s end expiratory lung volume. This methodology has been described previously during leg exercise and supported arm exercise,12 and has been shown to be reliable and reproducible in COPD subjects.13,14 Heart rate (HR) and pulse oxygen saturation (SpO2%) were obtained with a forehead probe attached to a pulse oximeter (N200: Nellcor, Hayward CA). Subjects scored their dyspnoea and rate of perceived exertion (RPE) on a modified Borg scale reading 0 (‘‘nothing at all’’) to 10 (‘‘maximal’’).15,16 Subjects were also asked to comment on whether exercise was terminated due to dyspnoea, arm fatigue or a combination of both.
Statistical analysis The StatView statistical package was used for analysis (Version 4.57 1992–1996, Abacus Concepts Inc., California). Statistical guidelines were provided by Altman.17 All data are presented as mean7SD. The mean difference with the 95% confidence interval (CI) is included where appropriate. The measurements taken during both exercise tests were compared using a paired t-test. Significance was set at po0.05.
Results Mean anthropometric data and lung function results for the 30 COPD subjects are presented in Table 1.
Responses at the end of exercise Exercise tests All subjects performed a symptom-limited, incremental, supported arm exercise test to peak work capacity and, on a separate day, performed a symptom-limited, constant-load, supported arm exercise test which represented a single-bout of endurance arm exercise training. The arm exercise tests utilised an electrically braked bicycle ergometer (SeimensElma; Solina, Sweden), modified for arm work (i.e. the gear system was mounted on an adjustable table and pedals were
The metabolic and ventilatory responses in the COPD subjects can be found in Table 2. There was no significant difference in the duration of the incremental test and the constant-load test. The work rate performed during the constant-load test averaged 6 W less than that performed during the incremental test. Despite this, there was a significantly higher VE, VE/MVV, VT, dyspnoea and RPE for the constant-load test compared to the incremental test at end
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exercise. The predominant symptom reported by subjects as the reason for stopping exercise during both the incremental test and constant-load test is given in Figure 1. Of the 15 subjects who reported arm fatigue as the reason for terminating incremental arm exercise, nine of these subjects also reported arm fatigue as the reason for terminating the constant-load test while the remaining six subjects complained of both arm fatigue and dyspnoea at the end of the constant-load test.
Table 1 data.
Baseline anthropometric and lung function
Baseline (mean7SD) Age (yr) BMI (kg/m2) FEV1 (L) % pred FVC (L) % pred TLC (L) % pred FRC (L) % pred RV (L) % pred
6578 26.375.4 1.570.4 56712 3.070.7 78713 6.771.3 117717 4.471.2 134729 3.771.1 170748
Definition of abbreviations: BMI:body mass index, FEV1: forced expiratory volume in one second, FVC:forced vital capacity, TLC:total lung capacity, FRC:functional residual capacity, RV:residual volume, yr:year, kg/m2:kilograms per metre, L:litre, % pred:percentage of predicted.
Responses throughout exercise The metabolic and ventilatory responses during the incremental test and constant-load test in a representative subject with COPD are shown in Figures 2 and 3, respectively. This subject’s responses corresponded to the pattern of exercise response seen by the group. There was a linear increase in both VO2 and VE with increasing work rate while the relationship of both VO2 and VE to time during constant work rate exercise tended to be curvilinear. VO2 started to plateau towards the end of the constant-load test. There was a curvilinear relationship of dyspnoea and RPE to work rate and dyspnoea and RPE to time. This pattern indicated that larger increases in dyspnoea and RPE occurred towards the end of exercise for a given change in work rate or time.
Both n = 11
Arm Fatigue n = 15
Dyspnea n=4
Both n = 13
Arm Fatigue n = 15
Dyspnea n=2
Figure 1 The number of subjects terminating arm exercise due to either arm fatigue, dyspnoea or both arm fatigue and dyspnoea in the (A) incremental arm exercise test and the (B) constant-load arm exercise test.
Table 2 End-exercise responses to incremental and constant-load arm exercise (including the mean difference between the parameters measured).
Work rate (W) (% of incremental) Duration (min) VO2 (L/min) VO2 (ml/kg/min) VCO2 (L/min) VE (L/min) VE/MVV VT (L) Fb (brths/min) SpO2 (%) HR (bpm) Dyspnoea RPE Change in EELV (L)
Incremental (mean7SD)
Constant-load (mean7SD)
Mean diff (95% CI)
33.0710.1
26.879.1 (80.975.6) 7.172.9 0.8370.2 11.173.0 0.9470.3 41.3714.4 80719 1.1870.3 3578 9673 109723 5.672.7 7.172.3 0.570.3
6 (5 to 7)
6.672.0 0.8270.2 11.073.0 0.9170.3 38.3711.8 73717 1.1270.3 3578 9873 109718 4.672.1 6.072.0 0.570.3
0.5 (0.5 to 1.5) 0.01 (0.3 to 0.5) 0.1 (0.3 to 0.6) 0.03 (0.02 to 0.1) 3 (0.9 to 5) 7 (3 to 11) 0.1 (0.001 to 0.1) 0.4 (0.8 to 1.6) 1.2 (2.3 to 0.01) 0.7 (6 to 8) 1 (0.1 to 2) 1 (0.5 to 2) 0.04 (0.1 to 0.04)
Definition of abbreviations: VO2:oxygen consumption, VCO2:carbon dioxide production, VE:minute ventilation, VE/MVV:ratio of minute ventilation to maximal voluntary ventilation, VT:tidal volume, Fb:breathing frequency, SpO2:pulse oxygen saturation, HR:heart rate, RPE:rate of perceived exertion, EELV:end-expiratory lung volume, min:minute, L/min:litres per minute, ml/kg/min:millilitres per kilogram per minute, L:litres, brths/min:breaths per minute, %:percentage, bpm:beats per minute. Significant difference between tests (po0.05).
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Figure 2 The physiological responses during the incremental arm exercise test in one representative subject (Subject 25) with COPD. (A) VO2, (B) VE, (C) dyspnoea and (D) RPE. (Abbreviations: VO2:oxygen consumption, VE:minute ventilation, RPE:rate of perceived exertion).
Discussion This study is the first to compare the physiological responses of a single bout of constant-load, supported arm exercise at an intensity of 80% peak work rate compared to incremental, supported arm exercise to peak work rate in people with COPD. The main findings were that the ventilatory, dyspnoea and arm fatigue responses at end exercise during the constant-load arm exercise were significantly higher than those at the end of the incremental arm exercise. In addition, more people with COPD indicated that arm fatigue or a combination of arm fatigue and dyspnoea limited exercise during both types of tests rather than dyspnoea alone. These results have implications for the initial prescription of arm training intensity for people with COPD. This study highlighted that the major limitation to arm exercise in this group of subjects with COPD was at the peripheral muscle level rather than due to ventilatory factors. The evidence for this comes from the fact that, at a similar VO2 for incremental and constant-load arm exercise, there was adequate breathing reserve (i.e. VE/MVVo80%) and more subjects terminated both forms of arm exercise because of arm fatigue rather than dyspnoea. As arm exercise is performed by a relatively small muscle mass compared to leg exercise, the peak ventilatory requirements of arm exercise in healthy subjects are low compared to leg exercise.18 Thus, in COPD subjects with only moderate lung impairment (FEV1 ¼ 56% predicted), the ventilation
required for arm exercise will not be high compared to the maximum ventilatory capacity such that arm fatigue could occur prior to ventilatory factors limiting exercise. Muscle fatigue has also been shown to be a factor limiting constant work rate leg exercise in COPD subjects. One study examined quadriceps muscle fatigue using twitch force measures following constant work rate leg exercise and demonstrated the existence of quadriceps muscle fatigue in 50% of the COPD subjects.19 Some studies have interpreted constant-load exercise tests based on critical power-duration considerations.20,21 While the measurement of critical power was beyond the scope of this paper, these studies are useful in understanding why the COPD subjects in the present study were unable to tolerate a work rate of 80% peak arm work rate. Critical power refers to the highest work rate, which can be sustained without exhaustion. Critical power for leg exercise in COPD subjects occurs at a lower absolute work rate than in healthy subjects but when represented as a percentage of peak work rate, it has been shown to be approximately 82% in COPD subjects and 68% in healthy subjects.21 These results indicate that COPD subjects can sustain higher relative leg work rates for training than healthy subjects.22 The fact that subjects in the present study were unable to sustain arm exercise at 80% peak work rate without exhaustion suggests that, for the arms of subjects with COPD, critical power (as a percentage of peak work rate) would be less than 80%. As the arm muscles in COPD subjects
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Figure 3 The physiological responses during the constant-load arm exercise test at 30 W in one representative subject (Subject 25) with COPD. (A) VO2, (B) VE (C) dyspnoea and (D) RPE. (Abbreviations: VO2:oxygen consumption, VE:minute ventilation, RPE:rate of perceived exertion).
have been shown to be well preserved,23 it could be argued that a relatively higher peak work rate for the arms could be achieved such that the critical power for arms now represents a lower fraction of the peak work rate (i.e. a response pattern for the arm muscles in COPD subjects similar to the critical power response seen in the leg muscles of healthy subjects). The only other studies which have examined both incremental arm exercise and endurance arm exercise at a constant work rate in people with COPD have used a moderate intensity for the constant work rate (i.e. p50% peak work rate).4,24 No statistical comparison of the responses was made between the two types of exercise in these studies. Despite this, on further review of the data, the physiological responses were higher at the end of the incremental exercise than at the end of the constant-load exercise. Working at a higher percent of peak work rate (i.e. 80% peak work rate) during constant-load exercise, as in our study, is likely to be above the critical power compared to working at a moderate percent of peak work capacity. This could explain the higher ventilation during constant-load exercise compared to incremental exercise (Figure 3B). Although more subjects stopped arm exercise because of symptoms of arm fatigue, dyspnoea scores were still high at end exercise for both forms of arm exercise. Our group has previously shown high dyspnoea scores at the end of incremental arm exercise which were not significantly different to those of leg exercise.12 The mechanism for the increase in dyspnoea scores during exercise has been studied previously with acute dynamic hyperinflation play-
ing a major role.13 The present study measured the EELV at end exercise during incremental and constant-load arm exercise and showed an increase in mean EELV of 0.5 L for both types of arm exercise. It is likely that this degree of dynamic hyperinflation was a contributing factor to the dyspnoea scores reported in the current study. The clinical implications of this study are significant. It is clear from the results that an initial high intensity arm training program for the length of time prescribed for aerobic benefits (i.e. approx.15 min) would not be possible as subjects were only able to exercise for a mean of 7 min.5 If attempted, subjects are unlikely to comply with training due to the high levels of perceived exertion and dyspnoea which would be experienced. Future research should examine whether high intensity interval training for the arms, in which bouts of high intensity exercise are interspersed with periods of rest or low intensity exercise, could be better tolerated. This study was limited to evaluating the physiological responses to supported arm exercise. As unsupported arm exercise is recognised as more representative of functional daily arm tasks than supported arm exercise for people with COPD, further studies are required to evaluate the ability of people with COPD to perform high intensity unsupported arm training. In conclusion, the results of the current study indicate significantly greater ventilatory, dyspnoea and arm fatigue responses at the end of exercise during high intensity, constant-load arm exercise compared to incremental arm exercise in people with COPD. This suggests that supported
ARTICLE IN PRESS Arm exercise in COPD arm training at an intensity of 80% peak work rate may be too high as an initial exercise prescription for people with COPD.
Funding This study was supported by the Australian Respiratory Council. This funding source was not involved in any aspect of study design or interpretation.
Conflict of interest The authors wish to declare no competing interests with respect to this work.
Acknowledgements The authors would like to thank Lissa Spencer for assistance in subject recruitment and the staff of the Respiratory Medicine Department at Royal Prince Alfred Hospital for the use of the lung function and exercise laboratory.
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