Coronary artery disease (CAD) is the leading cause of death worldwide and accounts for a significant disease burden in developing countries (1, 2). Cardiac rehabilitation (CR) is supported by evidence as key to CAD management and functional capacity is often a clinical outcome used to reflect the success of a CR programme (3). The 6-min walk test (6MWT) has been used as a prognostic tool to predict the risk of myocardial infarct, heart failure and death in CAD patients (4). The 6MWT demands no expensive or complicated equipment, however it does require a corridor which is at least 30 meters in length, and the full assessment procedure takes at least 20 min. Further, patient performance can be confounded by the motivation and unintentional encouragement provided by the operators (5). In contrast, the sit-to-stand (STS) test requires a chair and minimal space. It was first introduced in 1985 for the evaluation of lower limb muscle strength (6). Recently, an incremental STS test protocol was reported to be highly correlated with peak oxygen consumption during an exercise test in healthy individuals (7). STS tests are now considered feasible alternative tests for the assessment of functional fitness in older adults and in various patient populations (8–10).

Tests or measures in clinical medicine are normally used for three purposes: discriminate between patient characteristics, predict an outcome or inform the prognosis of a condition, and evaluate change over time or change after certain intervention (11). The STS tests have been used to discriminate levels of functional capacity in people with chronic respiratory illness (12, 13) and have also been used to evaluate the effect of pulmonary rehabilitation in people with chronic obstructive pulmonary disease (COPD) (14). The 1-min STS test was shown to be a strong predictor of 2-year mortality in people with COPD (15).

While the reliability and discriminative properties of various STS test protocols, including the five times sit-to-stand (FTSTS) test, 30-sec STS (30-s STS) test and 1-min STS (1-min STS) test, have been reported in different populations (16–18), a gold standard for testing the criterion validity of STS tests in discriminating levels of functional capacity in people with CAD is not yet available. There is therefore a need to establish the construct (convergent and known-groups) validity of STS tests in this population. Further, while STS test performance in patients with heart failure (19) and in patients enrolled in CR (20) have been reported, comparison of the reliability of various STS test protocols in patients with CAD has not been reported.

The focus of this current study is to examine the discriminative properties of the FTSTS, 30-s STS and 1-min STS tests. The primary objective of this current study is to examine the test-retest reliability, convergent and known-groups validity of the 3 STS tests. Convergent validity was examined through investigation of the correlation between STS test scores and the distance covered by the 6MWT, a valid test for measurement of functional capacity. Known-groups validity was examined through the evaluation of statistical and clinically important differences in STS tests of known groups, that is, participants with post-AMI and those without myocardial infarction (non-MI).

Following the assumption that STS tests are feasible alternative measurement tool for functional capacity, the secondary objective of the study was to explore the feasibility of using STS test protocols to discriminate the level of risk of cardiovascular events in people with CAD. Categorization of risk of cardiovascular events was adopted from a previous report, that patients who covered ≤ 419 m during a 6MWT were classified at high risk of cardiovascular events (4).

The use of FTSTS test has been shown to be an instrument of high reliability in healthy adults (33) as well as in people with spinal cord injury (34), hip arthroplasty (17) and in people with chronic obstructive pulmonary disease (12). The 1-min STS test and 30-s STS test were also shown to be reliable measures in people with pulmonary hypertension (22), total knee arthroplasty (35), with COPD (13) and cystic fibrosis (36). This current study is the first that compared all three STS tests in the same population of people with CAD. Findings of our study demonstrated excellent test-retest reliability for all 3 STS tests in this subject-cohort. Further, we found that compared to FTSTS and 30-s STS tests, the 1-min STS test induced the greatest changes in heart rate and SBP, and associated with the highest post-test fatigue score (Table 2). Amongst the 3 STS tests, changes induced by the 1-min STS test were closest to the physiological changes induced by the 6MWT. This suggests that the 1-min STS test is superior than 30-s STS and FTSTS tests if considered as an assessment tool for functional capacity in people with CAD. Our findings were in accord with a previous report which recommended the 1-min STS test to be a superior STS protocol for evaluation of functional capacity in subjects with COPD (8). Further, oxygen consumption was shown to be highest during a 1-min STS test compared to FTSTS in a cohort of patients with COPD (30). Although we have not measured oxygen consumption during the STS tests in our participants with CAD, we postulate that the pattern of oxygen uptake during STS tests would be similar in our subject cohort compared to those with COPD; further analysis is necessary to confirm this assumption.

As anticipated, findings of the current study illustrated moderate correlation between the 3 STS tests and the 6MWT, the correlation coefficient data of our study are similar to those previously reported in community-dwelling older adults (10) and in a cohort of patients with COPD (37). The correlation between LVEF and 6MWT and between LVEF and any STS tests was however only weak. This is not surprising. A lack of correlation between distanced covered in a 6MWT and ejection fraction was also reported in patients with heart failure (38). Exercise capacity was shown to be inversely associated with diastolic dysfunction but not associated with variation of left ventricular systolic function in people with LVEF within normal range (39). The LVEF of our patient cohort was all above 56%, it is therefore not surprising that there existed only a weak correlation between LVEF and exercise capacity (reflected by 6MWT or STS tests). While cardiac dysfunction partly contributes to poor exercise capacity, skeletal muscle fatigability plays an important mechanism in exercise tolerance (40); further, in patients with a normal ejection fraction, exercise capacity is associated with left ventricular dimensions (41), however, assessment of skeletal muscle fatigability and appraisal of left ventricular dimension was outside of the scope of this study.

The 6MWT has been suggested to be a prognostic tool for cardiovascular events in patients with stable CAD (4). Beatty and colleagues reported that patients in the lowest quartile of 6MWD of 87-419 m had 4 times the risk of cardiovascular events compared to those in the highest 6MWD quartile of 544-837 m. Based on Beatty and colleagues' work, we used 6MWD of 419 m to demarcate high or low-risk cardiovascular event groups. With ROC curve analysis of our data, we showed that the 3 STS tests demonstrated good discriminative ability to differentiate patients between high and low risk cardiovascular events. Results of this analysis suggest that for patients with CAD, those who required more than 11.7 sec to complete a FTSTS test, or those who completed <12 repetitions of STS sequence in 30 sec or <23 STS-repetitions in 1 min were subjected to higher risk of cardiovascular events.

The MDC₉₅ data generated from this study illustrated the measurement errors on repeated measurements of the STS tests. The MDC₉₅ value for FTSTS test was previously reported in patients with COPD to be 3.1s (12). Our study showed that the MDC₉₅ value for FTSTS test in people with CAD was 1.1s. This suggests that the measurement error of FTSTS test was less in our cohort of participants with CAD compared to people with COPD. Similarly, MDC₉₅ value for the 30-s STS test reported in subjects with COPD (42) was also higher than that generated in this study. The MDC₉₅ of 1-min STS test reported by Crook and colleagues (30) was however smaller than our results (2.2 repetitions compared to 3.86 repetitions in our CAD cohort). Direct comparison between our study and previous reports however may not be appropriate. As the MDC₉₅ in other reports were generated from tests conducted in patients with COPD, whose exercise capacity was limited by impairment of the ventilatory system, and our data were obtained from patients with CAD, whose functional capacity is often restricted by cardiac performance.

Smoking, hyperlipaemia, hyperglycaemia, and hypertension are known risks factors of cardiovascular disease (43). Table 1 shows that the rate of smoking is high amongst our participants. Unfortunately, China is the largest consumer of tobacco in the world (WHO-Tobacco in China) (44) and smoking prevalence is about 26.6% (45); there are more than 300 million smokers in China, this suggests that greater effort is required to foster public health strategies of smoking cessation.

In summary, this study showed that all 3 STS tests have excellent test-retest reliability. The MDC₉₅ values reported in this study provide a useful guide for the versatile use of STS protocols. The relationship of the STS tests with 6MWT demonstrated that these tests have good convergent validity in assessment of functional capacity in patients with CAD. Known-groups validity of these STS test was illustrated through distinct performance level by non-MI and post-AMI groups. STS tests are easy to perform and can be used as an assessment as well as an exercise training tool. Lastly this study inferred that STS test can also be considered as a discriminative tool to predict high or low risk of cardiovascular events in patients with CAD.

This is the first study that compared FTSTS test, 30-s STS test, and 1-min STS test in patients with CAD. This study showed that all 3 STS tests had good test-retest reliability, convergent and known-groups validity in assessing functional capacity in CAD patients. All 3 STS tests demonstrated good discriminative property in distinguishing patients with high and low risk of cardiovascular events and as such may inform the individualized clinical management, targeted exercise programmes and rehabilitation in this patient population.

The original contributions presented in the study are included in the article/supplementary material, further inquiries can be directed to the corresponding authors.

The studies involving human participants were reviewed and approved by the Ethics Committee of Xinhua Hospital Affiliated to Shanghai Jiaotong University School of Medicine (Approval Number: XHEC-C-2020-078-1). The patients/participants provided their written informed consent to participate in this study.

Study conceptualization: ZW, JY, SM, JL, JH, and AJ. Data curation: ZW, JY, SM, JL, YY, and TZ. Statistical analysis: RT and DE-A. Manuscript preparation and writing the first draft: ZW, JY, and SM. Writing the section of the manuscript: JL, YY, TZ, DE-A, RT, JH, and AJ. All authors contributed to manuscript revision and have read and approved the final version of the manuscript.

This work was supported by the National Natural Science Foundation of China (No. 31870936).

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

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