Maximal Exercise Test Results in Subacute Stroke

Article Outline

• Abstract
• Methods
  • Participants
  • Measures
  • Analysis
• Results
  • Feasibility of Exercise Testing Early Poststroke
  • Criteria for V̇o2max in Subacute Stroke
  • Test-Retest Reliability and Practice Effects of Maximal Exercise Testing
• Discussion
  • Feasibility of Exercise Testing
  • Measuring Maximal Aerobic Capacity: Vo2peak or V̇o2max?
  • Test-Retest Reliability and Practice Effects
• Conclusions
• Acknowledgments
• References
• Copyright

Abstract 

Tang A, Sibley KM, Thomas SG, McIlroy WE, Brooks D. Maximal exercise test results in subacute stroke.

Objectives

To establish the feasibility and reliability of graded maximal exercise testing, suitability of standard indexes of maximum oxygen consumption (V̇o₂max), and evidence of trial-to-trial practice effects in subacute stroke.

Design

Descriptive, cross-sectional study.

Setting

Rehabilitation hospital.

Participants

Consecutive sample of 35 participants (mean age, 65.7±2.6y; mean days poststroke, 17.6±2.2d).

Interventions

Not applicable.

Main Outcome Measures

Graded maximal exercise test using semirecumbent cycle ergometry. A subset (n=20) performed repeated tests to determine test-retest reliability and presence of practice effects.

Results

Thirty-one (89%) participants completed the exercise test without symptomatic responses (mean peak level of oxygen consumed [Vo₂peak], 10.7mL·kg⁻¹·min⁻¹; peak work rate, 39W). Twelve (34%), 15 (44%), and 3 (9%) participants achieved oxygen consumption per unit time (V̇o₂) plateau, respiratory exchange ratio, and heart rate criteria, respectively. Although test-retest correlations were high (intraclass correlation coefficient range, .67–.87), higher Vo₂peak (1.0mL·kg⁻¹·min⁻¹, P=.04) and work rate (7.3W, P=.01) were observed with repeated testing, with no associated increase in reaching standard criteria for V̇o₂max.

Conclusions

This work has important implications for developing guidelines for measuring aerobic capacity early after stroke. Although maximal exercise testing using semirecumbent cycle ergometry is feasible, standard V̇o₂max criteria are not consistently appropriate. At least 1 practice trial is recommended before the actual evaluation is performed.

Key Words:  Cerebrovascular accident , Exercise test , Outcome assessment (health care) , Rehabilitation

STROKE IS THE LEADING cause of adult disability in North America.¹ Given poststroke changes in neuromotor control,² increased energy demands associated with physical activity,³ and reductions in aerobic capacity early after stroke⁴ that persist into the chronic phase,⁵ the ability to perform basic everyday activities is compromised in stroke survivors. Although aerobic training is increasingly being recognized as an important component of stroke rehabilitation and testing protocols are being used to evaluate baseline fitness levels and determine the effects of exercise programs, there exist challenges to determining the true maximal aerobic capacity in this population.

A myriad of testing protocols have been developed to evaluate cardiorespiratory fitness in healthy people, the criterion standard being a progressive exercise test using breath-by-breath gas analysis to measure the maximum level of oxygen consumption (V̇o₂max) achieved.⁶ An observed plateau in V̇o₂ despite increases in work rate has been the primary criterion used to confirm that true V̇o₂max has been achieved.⁷ Relevant to the present study are observations that such indicators are not reliably achieved in special populations, including the elderly⁸ and people with coronary artery disease.⁹ Furthermore, with observations of plateau in V̇o₂ ranging from 30% to 95%,¹⁰ there is considerable debate as to whether plateau is a valid indicator of V̇o₂max even in healthy people.¹¹ Therefore, other physiologic responses are also used as secondary criteria for confirming maximum effort, including specific cutoff values of blood lactate levels, respiratory exchange ratio (RER), or percentage of age-predicted maximal heart rate; however, these indicators also remain controversial.⁸

Traditional testing protocols used for healthy populations may require modification for people with stroke. Historically, maximal exercise testing has not been regarded as feasible in the “high-risk” stroke population, and the ability to perform such a test is thought to be limited by the severity of neuromotor impairment, the reduction in functional muscle mass, the decreased oxidative capacity of the paretic muscles,³ and the presence of comorbid health conditions.¹² Studies that have evaluated aerobic programs in stroke have used the American College of Sports Medicine (ACSM) criteria for test termination,¹³ either in their entirety¹⁴, ¹⁵ or specific components only.², ¹⁶, ¹⁷, ¹⁸, ¹⁹ Indeed, the criteria used for establishing maximum aerobic capacity are inconsistent in the current stroke literature, with RER cutoff values ranging from greater than 1.0²⁰ to 1.15,², ¹⁶, ²¹, ²² heart rate as a plateau¹⁶ or reaching age-predicted maximal heart rate,¹⁵ or oxygen consumption per unit time (V̇o₂) change less than 1.5mL·kg⁻¹·min⁻¹ in the final minute of exercise.¹⁶ Given these issues with measuring maximal aerobic effort after stroke, the highest, or peak, level of oxygen consumed (Vo₂peak) is commonly used to describe aerobic capacity instead. Peak Vo₂ may or may not be representative of V̇o₂max,³ and it is unclear by how much they differ.

The evaluation of aerobic capacity after stroke remains an important matter in creating exercise programs and to evaluate change associated with training. To date, there have been only a few studies that have investigated the feasibility²² and measurement properties¹⁶ of exercise testing in the chronic phase after stroke and the feasibility of graded exercise testing in the early poststroke period.²³ In addition, there is a need to determine if there are differences on repeated testing to evaluate the presence of practice effects in this population.

The primary objectives of this study were (1) to establish the feasibility of graded maximal exercise testing with people in the early (subacute) poststroke period, (2) to examine the ability to meet traditional criteria for maximal capacity, and (3) to establish the test-retest reliability and evidence of intertrial practice effects. We hypothesized that early after stroke, patients who have cleared the appropriate medical screening would be able to perform maximal exercise testing using a ramp protocol on a semirecumbent cycle ergometer without adverse effects. We anticipated that study participants would not be able to achieve maximal aerobic effort as defined by traditional criteria for V̇o₂max (ie, plateau in V̇o₂, RER >1.0, or achievement of 85% of age-predicted maximum heart rate), making Vo₂peak a more appropriate descriptor of aerobic capacity in this population. We also hypothesized that there would be evidence of a practice effect in which participants would show an improvement in measures of aerobic capacity with repeated maximal exercise testing.

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Methods 

The study procedures were followed in accordance with institutional guidelines and were approved by the local university and hospital research ethics committees. Informed written consent was obtained from all study participants. This study was part of a larger ongoing trial examining the effect of aerobic exercise in the subacute stroke population.

Participants 

Forty-four patients in the subacute stage after stroke (medically stable and <3mo poststroke) were recruited from a rehabilitation facility and were screened. Inclusion criteria were ability to provide informed consent, ability to understand the evaluation procedures, and a Chedoke-McMaster Stroke Assessment (CMSA) leg impairment score greater than 2 (where active voluntary movement is present without facilitation²⁴). Seven patients were excluded because they exhibited contraindications outlined by the ACSM,¹³ musculoskeletal impairments, or pain. A total of 37 participants were enrolled into the study.

Participant characteristics noted included age, sex, lesion type and location, time poststroke, degree of neurologic deficit (motor, sensory, aphasia, apraxia, neglect) using the National Institutes of Health Stroke Scale (NIHSS)²⁵ and functional ability using the FIM instrument.²⁶ Level of leg motor impairment was assessed using the CMSA, where a score of 1 indicates flaccid paralysis, 3 describes a limb where spasticity and weakness are marked, and 7—the maximum score—indicates normal limb function including complex movement patterns with appropriate muscle timing and coordination.²⁴

Measures 

On entry into the study, all participants completed a graded maximal exercise test using a semirecumbent cycle ergometer.^a A subset of participants (n=20) performed 2 maximal exercise tests, separated by 1 to 4 days. The same equipment and research personnel (physical therapists, kinesiologists) were used for both tests to ensure consistency of testing conditions. The ramp protocol included a 2-minute warm-up at 10W at a target cadence of 50rpm, followed by progressive 5-W increases in work rate every minute. We designed this protocol specifically for the study, considering issues with strength and fatigability poststroke and anticipating a total test time of 8 to 10 minutes. A metabolic cart^b measured respiratory gas exchange with calculated averages at 30-second intervals per American Thoracic Society/American College of Chest Physicians (ATS/ACCP) guidelines to minimize breath-to-breath variability while determining peak ventilation values.⁷ For this high-risk population, blood pressure was taken from the nonparetic arm using an automated system,^c heart rate was measured with a heart rate monitor,^d and a 5-lead electrocardiogram^e was monitored for abnormalities. Handlebar supports were available on the cycle ergometer and were used as needed; participants were instructed to relax the arm during blood pressure measurement. The physician associated with this study was present when additional medical supervision was deemed necessary. The foot on each participant’s hemiparetic side was secured to the pedal as needed. The test was conducted and terminated according to ACSM¹³ criteria or terminated if a participant was unable to maintain the required pedaling rate despite cueing. Peak Vo₂ and peak heart rate were determined as the highest values reached during the exercise test. Ventilatory threshold (VeT), defined as the point where ventilation increases at a greater rate than V̇o₂,²⁷ was determined graphically from the respiratory gas exchange measures obtained during the ramp function test using the method described in ATS/ACCP guidelines.⁷

Analysis 

From the ramp function test, 3 criteria were used to evaluate participants’ ability to reach maximum aerobic capacity (ie, V̇o₂max): (1) plateau in V̇o₂ at the end of the exercise test based on the ACSM formula used to determine oxygen cost at each work rate, individually defined for each participant¹³; (2) RER greater than 1.0, and (3) peak heart rate within 10 beats per minute of the age-predicted maximal heart rate.²⁸ Because predicted maximal heart rate can decrease by 25% to 30%²⁹ for participants on β-blocker medications, the formula was adjusted accordingly to 70% (208 – [0.7 × age]).

Descriptive statistics were performed on all measures. The frequency and percentage of participants who achieved the criteria for V̇o₂max were determined from the maximal exercise test. For the subset of participants who completed 2 exercise tests, intraclass correlation coefficients (ICCs) were calculated to determine test-retest reliability, and paired t tests were used to determine significant differences between trials with respect to Vo₂peak, RER at the end of the exercise test, peak heart rate and work rate, and VeT. No adjustments were made to the critical P values. SigmaStat^f was used for statistical analysis.

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Results 

Feasibility of Exercise Testing Early Poststroke 

Of the 37 participants enrolled in the study, 2 showed abnormalities in blood pressure or electrocardiographic readings at the start of the exercise tests despite medical screening and were unable to continue the test. These abnormalities resolved after stopping the test, and these participants were subsequently withdrawn from the study. Thus, 35 participants performed the graded maximal exercise test. Participant characteristics are presented in table 1. Thirteen (37%) participants did not require any aids for ambulation, 5 (14%) used a cane, 11 (31%) used a walker, and 6 (17%) were nonambulatory. Results from the maximal exercise tests are presented in table 2.

Table 1. Participant Characteristics (n=35)

Characteristics	Values
Men/women	19/16
Type of stroke: ischemic/hemorrhagic/unknown	25/8/2
Hemiparetic side: right/left/bilateral	16/17/2
Age (y)	65.7±2.6(19−90)
Time poststroke (d)	17.6±2.2(6−62)
Medications: β-blockers/ACE inhibitors/both/none	5/16/2/12
Comorbidities
Hypertension	23
Cholesteremia	10
Diabetes mellitus	4
Coronary artery disease	7
Chronic obstructive pulmonary disease	3
History of smoking	9
NIHSS score⁎	4.3±0.4(1−9)
CMSA leg score	4.7±0.2(3−6)
FIM instrument score	87.5±2.7(57−114)

NOTE. Values are n or mean ± standard error (SE) (range) unless noted otherwise.

Abbreviation: ACE inhibitors, angiotensin-converting enzyme inhibitors.

Table 2. Results From the First Trials of the Maximal Exercise Tests (n=34)

Thirty-one (89%) participants completed the graded maximal exercise test without incident. Of these, reasons for stopping the graded maximal exercise test included participant choice without specified detail (n=10); breathing effort (n=2); generalized fatigue (n=1); or nonaerobic issues such as leg fatigue (nonparetic leg, n=8; hemiparetic leg, n=1), drop in pedaling rate (n=5), leg pain or discomfort due to premorbid conditions (eg, gout, knee pain) (n=2), mask and/or nosepiece discomfort (n=1), or when a participant’s foot was not adequately secured to the pedal (n=1). Four (11%) tests were stopped by the examiners when abnormal blood pressure responses were observed, per ACSM guidelines¹², ¹³: hypertensive responses (systolic blood pressure >210mmHg or diastolic blood pressure >115mmHg) when exercising at high work rate (n=2) or a drop in blood pressure of greater than 10mmHg despite an increase in work rate (n=2). These participants were closely monitored after test termination. There were no other symptoms or electrocardiographic abnormalities observed or adverse effects during or after these tests.

Criteria for V̇o₂max in Subacute Stroke 

The number of participants who achieved criteria for V̇o₂max, along with reasons for test termination, are presented in table 3. One participant was not included in this analysis because of equipment issues that prevented measurement of V̇o₂. With respect to each of the 3 criteria for V̇o₂max, 12 (34%) participants showed a plateau in V̇o₂ at the end of the exercise test, 15 (44%) participants achieved an RER value greater than 1.0, and 3 (9%) participants reached a peak heart rate within 10 beats per minute of the age-predicted maximal heart rate. Of the 12 (34%) participants who showed a plateau in V̇o₂ at the end of the exercise test, reasons for stopping were aerobic (participant choice, breathing effort, generalized fatigue) in 4 participants, nonaerobic (leg fatigue, inability to maintain pedaling rate or affix foot to pedal, pain/discomfort) in 5 participants, and related to blood pressure in 3 participants. For 9 of the 15 participants who reached RER greater than 1.0, tests were stopped for aerobic reasons, 5 for nonaerobic reasons, and 1 for blood pressure−related reasons. With respect to the heart rate criterion, 2 participants stopped the test for aerobic reasons and 1 stopped for nonaerobic reasons.

Table 3. Reasons for Test Termination and Achievement of Criteria for V̇o₂max (n=34)

Test-Retest Reliability and Practice Effects of Maximal Exercise Testing 

A subset of 20 participants who completed 2 maximal exercise tests was considered for analysis of test-retest reliability and practice effects. Participant characteristics are presented in table 4. The tests were separated by 1 (n=12), 2 (n=3), 3 (n=3), or 4 days (n=2). Results from the 2 trials of the maximal exercise test are presented in table 5. ICCs were calculated for test-retest reliability and ranged from .35 to .74 (see table 5). There was a 10% increase in Vo₂peak in trial 2 compared with trial 1 (t₁₉=−2.21, P=.04) and a 21% increase in peak work rate in the second trial (t₁₉=−2.84, P=.01). There were no statistically significant or clinically important differences in RER values (t₁₉=−1.92, P=.07), VeT (t₁₉=−2.024, P=.06), or peak heart rate (t₁₉=−1.5, P=.15) between trials.

Table 4. Characteristics of Subset of Participants Who Performed Repeated Testing (n=20)

Characteristics	Values
Men/women	12/8
Age (y)	69.3±2.3(49–87)
Time poststroke (d)	18.6±3.1(7–62)
Type of stroke: ischemic/hemorrhagic/unknown	14/6/0
Hemiparetic side: right/left/bilateral	8/10/2
Medications: β-blockers/ACE inhibitors/both/none	0/14/2/4
NIHSS score⁎	4.5±0.6(1–9)
CMSA leg score	4.7±0.3(3–6)
FIM instrument score	87.1±3.5(58–114)

NOTE. Values are n or mean ± SE (range) unless noted otherwise.

Table 5. Results From the Repeated Maximal Exercise Tests (n=20)

Abbreviation: CI, confidence interval.

In this subset of 20 participants, none were able to achieve all 3 criteria for V̇o₂max in either trial. In addition, there were no significant differences in occurrence of participants reaching criteria for V̇o₂max on the second test compared with the first test. In trial 1, 4 (20%) achieved 2 of the 3 criteria, 11 (55%) achieved only 1 criterion, and 5 (25%) did not achieve any; in trial 2, 2 (10%) participants met 2 of the 3 criteria, 11 (55%) met only 1 criterion, and 7 (35%) did not achieve any. Overall, 4 participants showed an increase in number of criteria met by trial 2 compared with trial 1, 7 participants achieved fewer criteria on trial 2, and 9 remained the same.

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Discussion 

Feasibility of Exercise Testing 

Based on the high percentage of participants (89%) who completed the test without symptomatic responses requiring test termination per ACSM safety criteria,¹³ the evaluation of aerobic capacity using maximal exercise tests is feasible and safe in the subacute stroke population, provided pretest medical screening is conducted along with ongoing monitoring during testing. Together with the lack of harm observed in other studies,⁵, ¹⁵, ¹⁶ these findings may begin to provide evidence that exercise testing is safe in the stroke population. The issue requires further investigation.

For 6 participants, the exercise tests were not conducted or were terminated by the investigators because of hypertensive responses or dropping blood pressure despite increases in work rate. In our study, systolic blood pressure that was higher than 210mmHg was considered hypertensive, lower than the 250mmHg suggested by the ACSM.¹² Use of a more conservative approach to monitoring systolic blood pressure than that given in the ACSM guidelines may have contributed to the frequency of symptomatic responses observed with exercise testing. Future studies need to examine the criteria for test termination in this population. Nevertheless, 11% of tests were halted for symptomatic response as observed in the current study, further highlighting the importance of ongoing monitoring and compliance with specific testing guidelines to minimize risk.

With Vo₂peak values of 10 to 11mL·kg⁻¹·min⁻¹ comparable with those reported by Kelly et al,³⁰ our results confirm that aerobic capacity is significantly compromised early after stroke and is lower than the 15mL·kg⁻¹·min⁻¹ required for independent living.⁴ Further, when ventilatory threshold relative to Vo₂peak (VeT percentage of Vo₂peak) is considered (see table 5), the values observed in the current study are higher than the 45% to 65% that would be expected in young healthy people and the 52% to 60% expected in older populations, providing additional evidence of compromised aerobic capacity in this population.

Previously, it has been recommended that submaximal, rather than maximal, exercise testing protocols be used in the early poststroke period.³¹ However, from a sample of 17 participants with subacute stroke, Kelly³⁰ reported that extrapolated Vo₂peak values from submaximal exercise tests were higher than those achieved during maximal exercise tests. This overestimation would have implications for exercise prescription, because inappropriately high target training zones might be prescribed based on this predicted V̇o₂max. Indeed, the contrary perspective may be that results from maximal exercise tests could be underestimating aerobic capacity in this population and, in fact, that submaximal testing may be more accurate in determining capacity. Valid measures of cardiorespiratory fitness early after stroke must be established to avoid the possibility of overtraining or undertraining patients in this important stage of recovery.

Measuring Maximal Aerobic Capacity: Vo₂peak or V̇o₂max? 

Although the current study shows the feasibility of symptom-limited maximal exercise testing, the issue remains of whether or not participants achieved peak levels or true maximum levels of exercise according to the criteria for V̇o₂max, an issue even in healthy people. The findings support our hypothesis that participants in the early stages poststroke would not be able to achieve criteria for V̇o₂max. Although 25 (74%) of the 35 participants met at least 1 criterion for V̇o₂max, only 34% showed a plateau in V̇o₂ at the end of the exercise tests, traditionally considered the primary criterion for determining maximal aerobic effort. Only 1 (3%) participant was able to achieve all 3 criteria. Our findings, along with the study by MacKay-Lyons and Makrides,⁴ support the consideration of secondary criteria to assist in determining if true maximal aerobic capacity was reached. Indeed, even in healthy people, the failure to reach a plateau in V̇o₂ is not a decisive factor in ruling out the achievement of true V̇o₂max.¹¹ With respect to the RER criterion, we chose a cutoff value of 1.0, as did MacKay-Lyons and Makrides⁴ in their evaluation of the aerobic capacity of subjects in the subacute phase of stroke. In agreement with their findings, RER was the most frequently achieved criterion we observed. Although other studies also used RER as a secondary criterion for V̇o₂max in the stroke population, the cutoff values varied (ranging from 1.0¹⁹, ²⁰ to 1.1¹⁵, ¹⁷ and 1.15¹⁶, ¹⁸, ²¹), and the frequency of study participants who achieved this specific criterion was not reported.

The least frequently achieved criterion in the current study was heart rate. Yates et al²³ defined maximal effort using heart rate response only (>90% of predicted maximal heart rate), which was achieved by 24% of their sample. MacKay-Lyons and Makrides⁴ adjusted predicted maximal heart rate for β-blockade to 85% (220 − age) if applicable and reported that 55% of the sample achieved this heart rate criterion. Compared with these previous studies, despite a more conservative adjustment for β-blocker use to 70% (age-predicted maximal heart rate), results from the current study showed an even lower frequency: only 9% of participants achieved this criterion. Pending further research into this area, using heart rate response per the ACSM guidelines¹² may not be a realistic criterion for determining maximal aerobic capacity in the early poststroke phase. Further, the ventilatory threshold occurring at 87% of Vo₂peak (see table 5) also provides further evidence that true V̇o₂max may not have been reached.

More participants’ tests were stopped for nonaerobic reasons (n=17) than for aerobic ones (n=13) (see table 3), suggesting that for a subset of the subacute stroke population, cardiorespiratory factors are not limiting performance on maximal exercise tests and that true V̇o₂max was not reached in all participants. Poststroke impairments in strength, coordination, muscle endurance, and sensorimotor control contribute to difficulties in pedaling at a high work rate. These findings are consistent with other studies that have used cycle ergometry as the testing modality for people with stroke³⁰ and for healthy people who are unfamiliar with pedaling as a method of exercise.⁷ However, of participants whose tests were terminated for nonaerobic reasons, most achieved at least 1 of the 3 criteria for V̇o₂max (12 [92%] of 13 participants]). Similarly, all 4 participants whose tests were stopped because of abnormal blood pressure responses met at least 1 criterion for V̇o₂max, suggesting that they may have been approaching maximal exercise capacity when the test was terminated.

Although it is likely that specific criteria for V̇o₂max, such as the age-adjusted maximum heart rate, may not be suitable in this clinical population in part because of the effects of cardiovascular medications, the lack of consistency in achieving plateau in V̇o₂ or RER greater than 1.0 may be more appropriately addressed by carefully adapting the testing modality. Certainly a seated model, particularly in the semirecumbent position, is a more appropriate testing modality for the subacute stroke population given potential challenges in postural control and limb placement, compared with upright ergometry or walking. Arguably, the use of a conventional semirecumbent ergometer with linked cranks may not help address the potential problems arising from local limb fatigue related to motor dyscontrol or asymmetry. As such, new approaches for conducting maximal exercise tests that reduce the occurrence of test termination for reasons other than reaching maximum capacity are under investigation.

In contrast to the present results, studies focusing on chronic stroke have reported that a range of study participants were able to meet any or all of the specified criteria: as low as 9% during treadmill testing¹⁵ and 100% with cycle ergometry.¹⁶, ¹⁸, ¹⁹ The findings from the latter 3 studies indicate that both testing modality and stroke chronicity may influence the utility of maximal exercise tests to evaluate cardiorespiratory fitness, suggesting that the chronic stroke population may achieve maximal limits of aerobic capacity more readily than the subacute population. In the healthy population, maximal results from exercise testing performed on a cycle ergometer are typically 10% to 15% lower than treadmill testing,⁷ particularly for those who are not accustomed to pedaling. Cycle ergometry may have accounted for lower Vo₂peak values compared with previous studies that conducted treadmill testing in subacute⁴ and chronic stroke.¹⁵ The presence of modality-specific differences in exercise test results early after stroke has yet to be investigated.

Test-Retest Reliability and Practice Effects 

Other studies that have examined test-retest reliability with maximal exercise testing in chronic¹⁵, ¹⁶ and subacute stroke²³ reported strong correlations between trials; in contrast, we found moderate associations between the first and second tests on most outcomes (see table 5). Unlike the findings of Dobrovolny et al,¹⁵ who did not report trial-trial differences in aerobic capacity, the difference of 10% between Vo₂peak in trial 1 compared with trial 2 in the current study was significant and is greater than the accepted day-to-day variability of ±3% in repeated testing,⁷ suggesting the presence of a practice effect. An increase was also seen in peak work rate in trial 2 compared with trial 1, suggesting improved tolerance of these participants in pedaling at a higher work rate. Dobrovolny¹⁵ used an acclimatization treadmill trial without open-circuit spirometry before the actual evaluations, which may have eliminated any effect of practice. Although relatively short time frames between trials (1−4d) were selected to minimize the effects of natural recovery occurring early poststroke, it is possible that fatigue could have influenced and masked even greater improvement on the second test. Improved performance on the second trial was not associated with any additional improvement in reaching the criteria for V̇o₂max, further highlighting the limitations in applying these traditional criteria to the subacute stroke population. Increased familiarization with the laboratory environment and equipment and with the testing protocol may have contributed to this observed practice effect by easing participants’ anxiety and allowing them to feel more comfortable exploring their limits of exercise tolerance during the test. Of clinical importance is the issue of establishing training loads based on results of the exercise test. The ACSM recommends exercise programming for stroke survivors set at intensities of 40% to 70% of Vo₂peak.¹² If training intensity was based on the results of trial 1 only (Vo₂peak, 10.0mL·kg⁻¹·min⁻¹), training would only occur at 36% to 64% of the Vo₂peak achieved on trial 2 (11.0mL·kg⁻¹·min⁻¹). Further, without such practice effects removed, it is possible that postintervention changes observed may arise because of these systematic changes linked to repeated maximal testing, rather than to training-related improvements in aerobic capacity. Thus, at least 1 preliminary trial is recommended when testing in the early poststroke period to counteract any potential practice effect and to establish a more accurate baseline.

A limitation of the current study is the relatively small sample size, and thus the results may be underpowered. Future research to establish valid measures of cardiorespiratory fitness in the early poststroke period is warranted to accurately evaluate aerobic capacity. This is an important first step for establishing appropriate training intensities for exercise programming in this critical period of recovery. With respect to trial-to-trial practice effects, it is not known whether or not a stable baseline had been established using only 2 trials. Subsequent repeated testing may show continual increases in peak values. The minimum number of trials required to establish a stable baseline should be determined, but given the typically rapid rate of recovery in this early period, this may be difficult in the subacute phase poststroke. Finally, it will be important in future research to establish the relation between various modalities of testing in the stroke population and to determine the most appropriate mode and modality for patients with varying levels of motor control impairment and different stages of recovery to effectively evaluate true maximal aerobic capacity.

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Conclusions 

Maximal exercise testing with subjects with mild to moderate stroke using a semirecumbent cycle ergometer is safe and feasible even in the early stages after stroke onset. Medical prescreening and ongoing monitoring of participants’ responses to exercise are critical to minimize risk. We also recommend the use of the ACSM guidelines¹², ¹³ for test termination, but modified for a more conservative blood pressure testing endpoint. An essential result from the present work is the recommendation to perform at least 1 practice trial to minimize confounding of training-related benefits with any practice-related changes in maximum testing. Because the traditionally used criteria for determining V̇o₂max are not reliably achieved using this mode of testing, Vo₂peak may be used as the best estimate of aerobic capacity. Ongoing work is needed to develop testing modalities that allow people with stroke to reach the criteria for determining V̇o₂max.

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Acknowledgments 

We thank the following people for their help and support: Mark Bayley, MD, Lou Biasin, PT, Janice Komar, PT, and Jackie Lymburner, PT.

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• a Biodex Medical Systems, 20 Ramsay Rd, Shirley, NY 11967-4704.
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