Heart failure (HF) occurs due to abnormalities in the heart’s structure or function, resulting in a reduced capacity to deliver oxygen throughout the body [1,2]. In 2020, Indonesia ranked as the second-highest country globally in HF-related deaths [3]. Data from the 2018 Basic Health Research indicated that 1.5% of the Indonesian population, approximately 1,017,290 individuals, had been diagnosed with congestive HF by healthcare providers [3]. The rising prevalence of this condition highlights the critical need for early detection, prevention, and effective management strategies. Key risk factors include hypertension, diabetes, coronary artery disease, and lifestyle behaviors such as smoking and insufficient physical activity. Symptoms commonly associated with HF are shortness of breath, difficulty breathing while lying flat, episodes of nighttime breathlessness, fatigue, swelling in the ankles, and reduced exercise tolerance [1,4,5]. Severe exercise intolerance is associated with serious long-term effects, including a poor prognosis, higher mortality rates, and a decline in overall quality of life [6-9].

Exercise intolerance refers to a reduced ability to engage in physical activities, often presenting with noticeable symptoms such as fatigue or shortness of breath [5,7,10,11]. This condition may stem from various underlying factors, including compromised heart and lung function, muscle dysfunction, peripheral vascular abnormalities, and disrupted autonomic regulation [7,12]. As a result, assessing exercise capacity has become a key measure in evaluating exercise intolerance in HF patients, particularly in cases of systolic HF. In these patients, a lower left ventricular ejection fraction (LVEF) is often associated with greater limitations in exercise capacity compared to other forms of HF.

Assessing exercise capacity in HF patients often involves measuring VO₂ max, which reflects an individual’s maximum oxygen uptake [13]. Although direct testing is considered the gold standard for determining VO₂ levels, many healthcare facilities face challenges in performing cardiopulmonary exercise testing (CPX) due to limited resources and time constraints [7,14]. As an alternative, the 6-minute walk test (6MWT) is commonly used as an indirect measure of exercise tolerance in patients with HFpEF and is regarded as the gold standard among field-based assessments of exercise capacity [15-17]. This test evaluates submaximal functional capacity by recording the distance a person can walk on a flat surface within six minutes [18-21]. However, studies have noted that not all patients are able to complete the 6MWT [22].

The sit-to-stand (STS) test offers an alternative method for assessing lower limb strength and functional performance, which can be performed conveniently in small spaces [16,19,23-25]. Recent research indicates that the STS tests are space-efficient, safe, and a reliable substitute for the 6MWT in evaluating VO₂ levels in patients with HF [15,22,26]. This study, therefore, aimed to examine the correlation between the STS tests (5-time sit-to-stand [5-STS] and 30-second sit-to-stand [30sSTS]) and the 6MWT to provide insights into cardiorespiratory fitness in patients with chronic HF and systolic dysfunction.

This cross-sectional study was conducted at the Cardiovascular Outpatient Clinic of Universitas Brawijaya Hospital in Malang between September and November 2023, involving patients with chronic HF and systolic dysfunction. A total of 34 participants meeting the inclusion criteria were enrolled. Eligible participants were stable HF patients aged 21 years or older, classified as HF with mid-range ejection fraction (LVEF 40%–49%) or HF with reduced ejection fraction (LVEF <40%) undergoing at least 3 months of HF treatment, and providing informed consent.

Exclusion criteria included New York Heart Association class IV HF, neurological disorders (e.g., hemiparesis, paraparesis, or peripheral neuropathy in the lower limbs), balance disorders, scores below 26 on the Montreal Cognitive Assessment Indonesian version, musculoskeletal disorders, significant lower limb pain (numeric rating scale≥4), peripheral arterial disease, or inability to complete at least five chair stands or walk.

All participants underwent the same sequence of tests on a single day. Testing began with the 5-STS test, followed by the 30sSTS test, and concluded with the 6MWT. The tests were arranged in order of increasing intensity, with rest intervals of 5 minutes between the two STS tests and 30 minutes between the final STS test and the 6MWT to minimize fatigue. Hemodynamic parameters (blood pressure, heart rate, respiratory rate, and oxygen saturation) and fatigue levels (assessed using the Borg scale) were recorded before and immediately after each test. Both STS tests used a 43 cm chair without armrests, secured against a wall. During the STS tests (Fig. 1), participants began seated with their arms crossed over their chest and feet flat on the ground, performing the 5-STS test, followed by 30sSTS test. The 6MWT was performed in a closed 30-meter corridor, with participants walking as quickly as possible between two marked points for six minutes to assess the distance covered.

Data analysis was carried out using IBM SPSS Statistics 24.0 for Mac (IBM Corp.). The relationship between the STS tests and the 6MWT was analyzed by comparing the correlations of the 30sSTS and 5-STS tests with the 6MWT. Pearson’s correlation coefficient was applied for normally distributed data, while Spearman’s correlation coefficient was used for non-normally distributed data.

The study received ethical clearance from the Health Research Ethics Committee of Dr. Saiful Anwar General Hospital Malang (Approval number: 400/207/K.3/302/2023) and obtained a Research Conduct Permit (Approval number: 16/UN10.F08.16.58/PP/2023). Written informed consent was obtained from all participants prior to data collection.

The study included 62 patients with chronic HF, of which 28 were excluded due to conditions such as cognitive, neurological, or musculoskeletal disorders, peripheral arterial disease, and unstable hemodynamics. As a result, 34 patients met the inclusion criteria. Importantly, none of these participants reported significant adverse effects, such as shortness of breath, fatigue, chest pain, fainting, falls, or other symptoms. Baseline characteristics are presented in Table 1.

The mean values recorded for the 5-STS, 30sSTS, and 6MWT were 13.90±4.72, 13.29±3.38, and 463.65±87.04, respectively. Analysis revealed that the 5-STS test had a moderate inverse relationship with the 6MWT (r=-0.436, p=0.01), indicating that shorter completion times in the 5-STS were associated with better 6MWT performance (Fig. 2A). In contrast, the 30sSTS test demonstrated a strong positive correlation with the 6MWT (r=0.629, p<0.001), suggesting that a higher number of repetitions in 30 seconds corresponded to better 6MWT results (Fig. 2B).

Both the 30sSTS and 6MWT showed a negative correlation with LVEF, with r=-0.420 (p=0.013) and r=-0.348 (p=0.044), respectively. However, the 5-STS test did not show a significant correlation with LVEF but exhibited a significant positive correlation with body weight (r=0.402, p=0.019).

The current research revealed a significant relationship between the STS tests and the 6MWT, with the 5-STS test showing a moderate inverse correlation (r=-0.436, p=0.01) and the 30sSTS test demonstrating a stronger positive correlation (r=0.629, p<0.001). A prior study by Fuentes-Abolafio et al. [22] found similar results when comparing the 5-STS test to the 6MWT for assessing aerobic capacity (VO₂) in elderly patients with diastolic HF, reporting a moderate inverse correlation with peak VO₂ (r=-0.55, p<0.001). The study concluded that diastolic HF might impair physical function and exercise capacity more severely than systolic HF due to abnormalities in skeletal muscle metabolism, mitochondrial function, and atrophy-related gene expression [12,22,27].

Another study by Adsett et al. [28], involving 49 HF patients undergoing a 12-week rehabilitation program, showed a strong correlation between the 5-STS and 60sSTS tests with the 6MWT (r=-0.70 and 0.76, respectively) and the Timed Up and Go test (r=0.79 and -0.77). However, participants performing the 60sSTS reported more fatigue compared to the 5-STS and 6MWT. Previous research has consistently supported the effectiveness of the 30sSTS and 5-STS tests in assessing lower limb strength and endurance [29,30]. Zhang et al. [31] suggested that shorter STS tests evaluate lower limb strength, while longer tests are better for measuring endurance. Similarly, Albalwi and Alharbi [32] concluded that the 5-STS test was better suited for assessing muscle strength and speed, whereas endurance was reflected more accurately in longer STS tests.

Studies by Fuentes-Abolafio et al. [22] and Bohannon et al. [24] emphasized that shorter STS tests may be less reliable in measuring endurance compared to the 10-STS or 30sSTS. Gurses et al. [33] corroborated this finding, demonstrating that the 30sSTS and 60sSTS tests had stronger correlations with the 6MWT (r=0.611 and r=0.647, respectively) than the 10sSTS (r=0.344, p=0.028). The stronger correlation of the 30sSTS and 6MWT with LVEF may stem from hemodynamic changes, which are less pronounced in the 5-STS test. Morita et al. [34] found that STS tests requiring higher repetitions caused greater changes in heart rate and systolic blood pressure due to the increased cardiopulmonary and musculoskeletal effort involved [7].

In patients with HF, particularly systolic dysfunction, reduced cardiac output and impaired oxygen transport to myocytes result in diminished VO₂, reflecting poor exercise capacity [10,24,35,36]. Exercises like the STS test improve VO₂ through enhanced cardiac output, better muscle blood flow, and lower ventilation demand [36,37]. Peripheral muscle adaptations, including improved mitochondrial density and oxidative function, play a crucial role in increasing VO₂ efficiency, reducing cardiovascular strain during exercise. Such adaptations also enhance central function by improving oxygen transport and gas exchange during physical activity [38-40].

One strength of this study was its ability to assess cardiorespiratory fitness in a time-efficient manner within confined spaces. However, certain limitations must be acknowledged. The absence of a comparison with the gold-standard CPX test restricted the direct assessment of cardiorespiratory fitness using the 30sSTS and 5-STS. The study’s limited sample size also precluded a detailed comparison of STS test effects on systolic versus diastolic HF. Additionally, performing all tests on the same day might have induced fatigue in participants, although this was mitigated by monitoring vital signs, subjective feedback, and Borg scale scores.

Future research could enhance validity by incorporating CPX-based VO₂ assessments alongside Borg scale and metabolic equivalents (METs) evaluations to better understand the subjective experience of completing these tests. Increasing the sample size would allow for more robust conclusions regarding the suitability of the 30sSTS as an alternative to the 6MWT for assessing VO₂ and METs in chronic HF patients.