Physiological responses to maximal effort wheelchair and arm crank ...

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GLASER,RUGER M., MICHAELNSAWKA,MARY. F. BRUNE,. AND STEPHEN. W. WILDE. Physiological responses to maximal effort wheeLchair and arm crank ...
Physiological responses to maximal effort wheelchair and arm crank ergometry ROGER M. GLASER, MICHAEL N. SAWKA, MARY F, BRUNE, AND STEPHEN Laboratory of Applied Physiulugy, Department of Physiulugy, School of Medicine, Wright State University, Dayton 45435; and Physiology Research Laboratory, Veterans Administration Medical Center, Dayton, Ohio 45428

GLASER,RUGER

M., MICHAELNSAWKA,MARY F. BRUNE, Physiological responses to maximal effort wheeLchair and arm crank ergometry. J. Appl. Physiol.: Respirat. Envbon, Exercise Physiol. 48(6): 1060-1064, 19&I.The purpose of this investigation was to compare physical work capacity (PWC), peak oxygen uptake (peak J?O~), maximal pulmonary ventilation (VE,,,), maximal heart rate (HR,,,), and maximal blood lactate concentration (LAmax) for wheelchair ergometer (WERG) and arm crank ergometer (ACE) exercise. For this, wheelchair-dependent (rt = 6) and able-bodied (n = 10) subjects completed a progressive intensity, discontinuous test for each mode of exercise. Each test was terminated by physical exhaustion and/or an inability to maintain a flywheel velocity of 180 m min? Relatively high correlation coefficients were found between values obtained during the two modes of ergometry for PWC, peak vo2, ~~~~~~ and HR,,,. WERG exercise was found to elicit a significantly (P < 0.05) lower PWC (by 36%), HR,,, (by 7%), and LA,,, (by 26%) than ACE exercise. Peak vo2 and ~~~~~~ however, were similar for both exercise modes. These data suggest that either exercise mode may be used for fitness testing and training of people who cannot use their legs and that arm cranking may be a superior method to propel wheelchairs. AND

STEPHEN

W. WILDE.

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arm exercise; exercise capacity; propulsion

wheelchair

design; wheelchair

ARM CRANK ERGOMETRY HAS been used to exercise test (3,14,23) and train (18) individuals who cannot use their

legs for locomotion. This mode of ergometry, however, requires use of different musculature and biomechanics than wheelchair operation, which is the primary method of locomotion for this population. The concept of exercise specificity (17) suggeststhat a method of exercise resembling wheelchair activity may be advantageous for the testing and training of these individuals. This has resulted in several recent studies using wheelchair ergometer exercise for cardiorespiratory fitness testing (7, 15, 22) and training (8). To better interpret data from these studies, physiological responsesfor wheelchair ergometry could be compared to those for the well-studied arm crank ergometry. Wicks et al. (22) have compared physiological responses to maximal effort wheelchair ergometer and arm crank ergometer exercise and have found no differences for maximal heart rate (HRmax), maximal pulmonary ventilation (VE&, and peak oxygen uptake (peak %2). However, different protocols were used for 1060

W. WILDE

each mode of ergometry, and power output was not reported for wheelchair ergometer exercise. Therefore, the purpose of the present investigation was to compare physical work capacity (PWC) and cardiorespiratory responses for maximal effort wheelchair ergometer and arm crank ergometer exercise using identical test protocols. METHODS

Subjects. Six wheelchair-dependent (WD) and ten able-bodied (AB) volunteers participated in both wheelchair ergometer and arm crank ergometer exercise so that subjects from each population could serve as their own control. Physical characteristics of the test populations are presented in Table 1. Each subject was informed previous to all testing as to the purpose of the study, their extent of involvement, any known risks, and their right to terminate participation at will without penalty. Each expressed understanding by signing a statement of informed consent. The protocol and procedures used for this study have been approved by the Medical Human Subjects Review Committee of Wright State University. Instrumentation. To compare wheelchair ergometry with arm crank ergometry a combination wheelchair-arm crank ergometer was designed and constructed (see Fig. 1). The wheelchair ergometer (WERG) and arm crank ergometer (ACE) are both basically extensions of the popular Monark bicycle ergometer. Previous papers from this laboratory have described the WERG in detail (9, 11). The arm crank unit was inserted into the seat support of the Monark by a solid steel bar that was secured by a bolt and clamp. This mounting allowed the arm crank to be adjusted to the shoulder height of each subject. A chain and sprockets coupled the arm crank to the flywheel of the Monark bicycle ergometer. Standard gearing of the Monark was retained, so that for each wheelchair wheel and arm crank revolution the flywheel traveled 6 m. An electronic speedometer was observed by the subjects to maintain the required velocity (mm min-‘) of the Monark flywheel. In addition, an electronic odometer (wheel revolution counter) allowed calculation of the precise distance the flywheel traveled over a period of time. Protocol. Before experimental testing subjects completed several practice sessionson the WERG and ACE.

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1. Physical characteristics szlbject populations TABLE

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FIG. I. Combination wheelchair-arm crank ergometer: A is electronic speedometer; B is lengthened pendular arm, and C is expanded braking force scale.

The subjects were then randomly assigned to complete either a WERG. or ACE exercise test on a future date. The alternate activity was then performed within a 3-day to 2-wk period after the initial test. For both modes of ergometry, a progressive intensity, discontinuous test was used with exercise bouts 4 min in duration interspersed by 7-min rest periods. Recent investigations (16, 19) of maximal effort arm crank exercise have employed 4-min exercise bouts. The present study used 7-min rest periods between exercise bouts representing a compromise between the 5-min (19) and I@min (16) rest periods used in previously reported protocols. The initial power output (PO) for the test was extrapolated from submaximal HR vs. PO data obtained during three warm-up bouts (30, 90, and 150 kpmemin-‘). This initial PO corresponded to 75% of each subject’s predicted age-adjusted maximal heart rate (220 beats/min - age), corrected (-10 beats/min) fur arm exercise. Stenberg et al.

(21) have found that HR,,, averages approximately 11 beats/min lower for arm than for leg exercise. Each subsequent exercise bout was 60 kpmemin-’ greater than the preceding PO level. During each exercise bout subjects attempted to maintain a flywheel velocity of 180 me min-’ (30 wheelchair wheel or arm crank rpm), and braking forces were set to achieve the desired PO. Physiological data were collected during the last minute of each exercise period. Each exercise test was terminated by physical exhaustion and/or an inability to maintain a flywheel velocity of 180 m gmin-‘. Five minutes after completing the exercise test 200 ~1of blood were collected from a free-flowing digit puncture for maximal blood lactate (LAmaX) determination (1, 6, 13). Physiological uariabzes. Oxygen uptake (%%z,10min-’ STPD) and pulmonary ventilation (VE, l*min-’ BTPS) were determined by open-circuit spirometry. Subjects breathed via a two-way breathing valve (Daniels), and expired gases were collected in 150-liter Douglas bags. Expired gases were then analyzed for 02 and CO2 concentrations by an electrochemical 02 analyzer (Applied Electrochemistry S-3A) and an infrared CO2 analyzer (Beckman LB-2), respectively. Analyzers were calibrated before and during testing with room air and reference gases of known concentrations. Minute volumes of expired gases were measured by a dry gasometer (Parkinson-Cowan CD-4) that was previously calibrated against a 120-liter Tissot gasometer. The electrocardiogram was displayed on an oscilloscope and recorded (Electronics for Medicine VR-6) from chest electrodes (CM5 placement). Heart rate was continuously monitored by a cardiotachometer (Gedco CT2) during each exercise test. Blood lactate concentrations were determined by an enzymatic method (12), and automatic pipettes were used for all micropipetting. The absorbance value of each sample obtained by a spectrophotometer (Spectronic 20) was plotted on a standard lactate curve to obtain the corresponding LA concentrations. Statistical an&ysis. Means, standard deviations, standard errors of the means, Pearson product-moment correlation coefficients, and dependent t tests were calculated using a programmable calculator (TI-59 with printer). Statistical significance was tested at the P < 0.05 level. RESULTS

After completion of the warm-up bouts, the subjects completed an average of 2.2 bouts (8.8 min) and 2.7 bouts (10.8 min) on the WERG and ACE, respectively. Figure 2 presents the individual PWC, %z, VE, HR, and LA data obtained for maximal effort WERG exercise plotted against values obtained for maximal effort ACE exercise. In general, PWC, HR,,,, and LA,,, were higher for ACE exercise, whereas peak vo2 and ~~~~~ were scattered around the line of no difference. For each variable both the WD and AB groups exhibited a similar response pattern with respect to the line of no difference for both modes of ergometry. This was demonstrated statistically by the fact that t test results for each individual group were essentially the same as those obtained when both

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FIG, 2, Individual data for A, physical work capacity (PWC); B, peak oxygen uptake (peak J&); C, maximal pulmonary ventilation #Em,,); D, maximal heart rate (HR,,,); and E, maximal blood lactate (LAmaX) values in response to maximal effort arm crank ergometer (ACE) and wheelchair ergometer (WERG) exercise. Each point represents I individual, and 45” line represents no difference between two modes of ergometry. 2

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volume remains fairly constant. However, if lower cardiac output values were achieved for maximal WERG exercise, lower peak VO, values might be expected. I PWC, Peak ire?, VE mirx, HR rnax? 1 LA max, In agreement with the data of Wicks et al. (ZZ), we kpm-min-' 1.min-' l.min-' beats/min mmol~lpl found no difference in peak vo2 values between these two modes of arm ergometry. These findings suggest that ACE WERG ACE WERG,ACE WER&CE WERC: ACE WERG similar muscle masses were employed and that factors Mean 569 364 ! 1.77 1.73 r 71,8 71.5 169 158 8.4 6.2 limiting peak vo2 had similar effects for WERG and ACE &SE k44 k32 tO. 14 t0.14 k5.7 k6.5 t4 kO.6 kO.5 k-4 exercise. Peripheral factors (i.e., muscle perfusion and P NS NS to.01 to.01