Research ArticleOriginal Research

Translation of Exercise Test Response to Training Intensity Using the Count Scale

Hao-Yan Wang, Qing Miao, Qiu-Fen Xu, Xin He and Bo Xu
Respiratory Care February 2016, 61 (2) 220-224; DOI: https://doi.org/10.4187/respcare.04179

Abstract

BACKGROUND: Exercise testing is recommended before prescribing individualized exercise intensity. However, there are few data demonstrating how exercise test responses are translated into individualized training intensity using a simple method. We previously developed a simple method to rate dyspnea called the count scale, including the count scale number (CSN) and count scale time. The purpose of this study was to assess the CSN for translation of exercise test response to training intensity.

METHODS: Twenty-eight subjects (22 men and 6 women) with COPD age 66.6 ± 8.22 y participated in 2 exercise sessions. During the first session, in which exercise was guided by the heart rate, the CSN and heart rate were obtained (ie, CSN1 and HR1) while the heart rate was increased by 20% compared with the resting heart rate. During the second session, exercise was guided by the CSN. When the CSN was close to the CSN1, the CSN and corresponding heart rate were recorded as CSN2 and HR2. Differences between CSN1 and CSN2 and between HR1 and HR2 were compared. The relationship between HR1 and HR2 was analyzed. Agreement between HR1 and HR2 was evaluated by Bland-Altman plots.

RESULTS: No significant differences were seen between HR1 and HR2 (96 ± 11 and 97 ± 11, respectively; P = .14). A high correlation between HR1 and HR2 was found (r = 0.932, P < .001). The 95% CI for the difference between HR1 and HR2 was −1.2 to 8.5 beats/min.

CONCLUSIONS: Exercise guided by the CSN alone could result in a given heart rate response, suggesting that the CSN is a simple and practical tool in translating exercise test results into individualized training intensity. With the CSN as the intensity indicator, patients can exercise safely and effectively.

Introduction

Exercise is an important part of rehabilitation for patients with COPD. In order to minimize adverse events and obtain greater cardiopulmonary benefits, it is important for patients to be guided to exercise at a proper exercise intensity, because COPD patients have various exercise risks depending on their age, lung function impairment, and the presence of co-morbidities.1 Therefore, cardiopulmonary exercise testing is recommended before prescribing individualized exercise intensity.2,3 A major challenge in clinical exercise prescription is how to translate the exercise test response into an individualized training intensity that is suitable for use in a home-based rehabilitation program.

Target heart rate, based on estimated or assessed peak heart rate, is the most widely used objective approach for prescribing exercise training intensity.4,5 However, heart rate monitoring is impractical and inconvenient during home-based exercise for the majority of patients. The Borg scale for the ratings of perceived exertion and the talk test are widely used subjective methods. Although the Borg scale rating is self-reported and feasible, the subjects need to see the scale for rating during exercise. Furthermore, a study by Gondoni et al.6 found that level of education, gender, and the use of diuretics significantly affected the Borg scale rating. The talk test is another simple method to rate exercise intensity, and studies have shown that the talk test is a surrogate for the ventilatory threshold 7,8. However, there was considerable variability reported with the method,7 and the talk test depends on the subjective experience of the patient and thus allows room for error.

We previously developed a new method to rate dyspnea called the count scale, in which subjects inhale maximally and then count from 1 to the maximum number they can reach in 1 breath while exhaling.9 The count scale, including the count scale number (CSN) and count scale time, has been showed to be a sensitive reflection of exercise intensity. The purpose of this study was to assess the CSN for translation of a cycle ergometer exercise test response to training intensity during a treadmill walking task. We measured CSN and heart rate in 2 exercise sessions and hypothesized that the CSN corresponding to a target heart rate in the cycle ergometer would result in a similar heart rate response (ie, close to the target heart rate) in the treadmill walking session.

QUICK LOOK

Current knowledge

Exercise is an important part of rehabilitation for patients with COPD. In order to minimize adverse events and obtain greater cardiopulmonary benefits, it is important for patients to be guided to exercise at a proper intensity. A major challenge in clinical exercise prescription is how to transfer the exercise test response into an individualized training intensity suitable for home use.

What this paper contributes to our knowledge

In a group of COPD subjects, exercise intensity was measured by the count scale number and heart rate response. The count scale number is the highest number the patient can count to while exhaling after a maximal inspiration. In these subjects, exercise guided by the count scale number alone resulted in a desired heart rate response. The count scale number proved to be a practical tool in translating exercise test results into individualized training intensity.

Methods

Subjects

Twenty-eight subjects (22 men, 6 women) with COPD age 66.6 ± 8.2 y participated in this study from January 2014 to July 2014. Their baseline data are shown in Table 1. All subjects were clinically stable and provided written informed consent. The study was approved by the ethics committee of Beijing Friendship Hospital.

View this table:
Table 1.

Baseline Characteristics of the Subjects

Pulmonary Function Testing

Spirometry (MasterScreen CPX, CareFusion, San Diego, California) was performed in all subjects; FEV1 and FVC were recorded. Procedures were carried out according to American Thoracic Society/European Respiratory Society standards.10

Count Scale

Subjects wore a nose clip and breathed through the mouth. After taking a maximal inspiration, they counted out the Arabic numbers from 1 to as high as they could (ie, 1, 2, 3…) in one breath while exhaling. Subjects were instructed to speak loudly enough to be heard, at their usual talking volume, and without pausing between counting numbers. The highest number they spoke was recorded as the CSN.

In the first session, subjects exercised on an electronically braked cycle ergometer (ER 900L, CareFusion). Heart rate was recorded via electrocardiogram. The exercise work rate began with 20 W and was increased by 10 W every 2 min until the heart rate was increased by 20% compared with the resting heart rate. While cycling at that work rate, subjects performed the count scale. The CSN was recorded as CSN1, and the average heart rate during this period of measuring the CSN was recorded as HR1. In the second session, 30 min later, subjects exercised on a treadmill. The treadmill speed began with 2 miles/h and was increased by 0.5 miles/h every 2 min. The subjects were asked to perform the count scale during the last 30 s of each exercise stage. When CSN was close to CSN1 (ie, the difference was < ±5), the exercise test was terminated, and the CSN was recorded as CSN2. The heart rate averaged for this period of measuring the CSN2 was recorded as HR2. The CSN and heart rate were recorded separately by 2 researchers. The subjects and the researcher responsible for testing the count scale were blinded to heart rate.

Statistical Analysis

Data are presented as mean ± SD. Differences between CSN1 and CSN2 and between HR1 and HR2 were examined using a paired-samples t test. Linear regression analysis was performed to assess the relationship between HR1 and HR2. Agreement between HR1 and HR2 was evaluated by Bland-Altman plots. P < .05 was considered statistically significant.

Results

Twenty-eight subjects with COPD were involved in this study. All subjects completed the CSN testing with no adverse events.

All data, including HR1, HR2, CSN1, and CSN2, were normally distributed. No significant differences were seen between CSN1 and CSN2 (26.7 ± 7.2 and 26.4 ± 7.4, respectively, P = .53) and between HR1 and HR2 (96 ± 11 and 97 ± 11 beats/min, respectively, P = .14). Figure 1 shows a highly significantly correlation between HR1 and HR2 (r = 0.932, P < .001). As shown in Figure 2, the 95% CI for the difference between HR1 and HR2 was −1.2 to 8.5 beats/min.

Fig. 1.
Fig. 1.

Scatter plot of the correlation between HR1 and HR2 in subjects with COPD. HR1 was the target heart rate. HR2 was produced by the count scale number corresponding to HR1. There was a highly significant correlation between HR1 and HR2 (r = 0.932; P < .001).

Fig. 2.
Fig. 2.

Bland-Altman plot of difference in heart rate (target heart rate − responding heart rate) against the mean of the 2 heart rates. The 95% CI for the difference between the 2 heart rates was −1.2 to 8.5 beats/min. The blue line indicates a mean difference of −1.2, and red lines denote mean ± 1.96 SD.

Discussion

Although our previous work has shown that the count scale is a simple and reproducible method for COPD subjects to measure dyspnea during exercise,9 we have not previously studied how to translate exercise test response into training intensity using the count scale. Because exercise intensity is most often prescribed by using a target heart rate, we investigated the relationship between heart rate and CSN in subjects with COPD and found that exercise guided by the CSN corresponding to the target heart rate results in a heart rate that is similar to the target heart rate. The present study also indicated that the CSN was similar on different exercise modes when applying the same objective exercise intensity. This is the first study evaluating the validity of the count scale as a tool to translate exercise test response into a training intensity.

Although exercise training under supervision at the hospital is safe, home-based or community-based exercise training is the main way for the majority of stable patients to conduct pulmonary rehabilitation. Thus, it is important for patients to be instructed to exercise at a prescribed exercise intensity with a simple method. In this study, we designed 2 exercise sessions. In the first session, we measured the CSN at the target heart rate. In the second session, exercise was guided by the CSN, and we recorded the corresponding heart rate when the CSN was close to the CSN of the first session. There was no significant difference between the 2 heart rates, and the correlation was high (r = 0.932). The 95% CI for the difference between the target heart rate in the first session and the corresponding heart rate in the second session was relatively narrow (−1.2 to 8.5 beats/min), supporting the validity of the CSN as a tool for translating an exercise test response into a training intensity. It suggests that after we determine the target intensity in terms of VO2, because subjects are not allowed to speak during VO2 measurement, we can measure the CSN at the target heart rate corresponding to the target VO2 in another session. Consequently, the individualized target intensity can be translated to corresponding CSN, and patients can guide their exercise intensity by themselves using the CSN.

The talk test is a subjective method recommended for prescribing exercise intensity on the basis of the subjects' ability to speak comfortably during exercise. Over the last decade, several studies evaluating the validity of the talk test have been published.11–14 The talk test has been studied in healthy individuals and subjects with cardiovascular disease but not in subjects with chronic lung disease. Studies have shown that the talk test results in an exercise intensity that is near the ventilatory threshold, suggesting that the talk test may be a surrogate of the ventilatory threshold and can be used to prescribe exercise intensity not only for healthy adults11 and athletes15 but also for patients with coronary artery disease7,12 when exercise test data are unavailable. However, the ventilatory threshold does not guarantee risk-free exercise, especially for patients with chronic lung disease. It follows that, when used as a surrogate for ventilatory threshold, the talk test will similarly not guarantee risk-free exercise. Brawner et al7 showed that although the heart rate during exercise guided by the talk test was similar to the heart rate at ventilatory threshold, there was considerable variability (SD = 22–23% heart rate reserve), suggesting that the talk test has difficulty ensuring a safe exercise training intensity in each patient, especially in patients who may be at increased risk of adverse events during exercise. In the current study, the 95% CI for the difference between the target heart rate and the heart rate guided by the CSN was relatively narrow (−1.2 to 8.5 beats/min). The difference between the 2 heart rates was always < 10 beats/min. We think the error can be accepted in clinical practice.

In this study, we used number counting as a standard to gauge exercise intensity without any instruments. Any patient can be easily instructed to use it in any form of exercise training. The maximum number they can speak is inversely correlated with the intensity,9 since it depends on the expiratory time, which is shortened when the respiratory rate increases during exercise.16,17 Interestingly, this finding is very similar to a variation of the talk test, the counting talk test. Both the counting talk test and the count scale are semiquantitative tools and determine how high the patient can count before taking a second breath. The counting talk test has been shown to be useful in estimating exercise intensity in healthy adults.18,19 However, the counting talk test must be performed at rest as well as at each intensity stage of exercise testing, and there have been as yet no reports in patients.

A limitation of this study is that we have only studied the relationship between CSN and the target heart rate at one exercise intensity (ie, heart rate increased by 20% compared with the resting heart rate). Further work needs to be done at higher exercise intensities.

Conclusions

We have demonstrated that the CSN is a simple and useful tool in prescription of exercise. After exercise intensity assessment, using the CSN, we could easily translate desired exercise intensity into corresponding training intensity using the CSN. Finally, with the CSN as the intensity indicator, patients can exercise safely and effectively.

Acknowledgments

We thank Richard Casaburi PhD MD for assistance in editing and reviewing the manuscript.

Footnotes

  • Correspondence: Hao-Yan Wang MD, Department of Respiratory Medicine, Beijing Friendship Hospital, Capital Medical University, No. 95 Yong An Road, Xichen District, Beijing 100050, China. E-mail: haoyanw{at}ccmu.edu.cn.

  • This study was supported by Grant Shoufa 2011-2002-03 from the Capital Scientific Research Fund for Healthy Development. The authors have disclosed no conflicts of interest.

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