INTRODUCTION
The world's aging population is increasing, and it is projected that the elderly population will constitute about 30% of the global population by 2050.1) Aging is a significant risk factor for chronic diseases and it can trigger the onset of geriatric syndromes and illnesses due to changes in physiological systems.2,3) Hypertension is a prevalent condition in older adults, affecting >70% of them. It is associated with an increased risk of cardiovascular disease, cognitive decline, and physical disability.4) In addition, hypertension can accelerate the physical fitness decline related to sarcopenia, which is the age-related loss of muscle mass and strength.5,6)
Functional fitness plays a crucial role in promoting healthy aging by allowing individuals to maintain their independence and quality of life while performing daily tasks safely and without fatigue.7) The growing population of hypertensive individuals with limited functionality highlights the significance of early detection and interventions to alleviate the impact of hypertension on aging and disability.4,8) Assessing the muscular strength, endurance, balance, and stability of older individuals through commonly used tests like handgrip strength assessment, timed sit-to-stand tests, and the timed up and go test (TUG) is essential when evaluating their functional abilities and fall risk.9-11) These assessments demonstrate a strong correlation with other measures such as the five times sit-to-stand test (FTSST), and leg strength, highlighting their significance in evaluating functional abilities, especially among older individuals with hypertension.12,13)
Aerobic capacity, a key aspect of physical fitness, is commonly assessed in both healthy and diseased populations. The 6-minute walk test (6MWT) is commonly employed as a standardized assessment to evaluate submaximal functional aerobic capacity in older adults.14) However, the practicality of administering this test during routine outpatient consultations is limited due to the requirement of a 30-m hallway and the time-consuming nature of the test.14,15) As an alternative, simple and efficient office-based field exercise tests such as the 2-minute step test (2MST) can serve as valuable initial screening tools to assess functional status and guide subsequent treatment.16,17) The 2MST test exhibits a strong correlation with the 6MWT, indicating its potential as a measure of functional aerobic capacity.13,18,19)
The evaluation of functional fitness using existing tools can present challenges due to variations in body composition, physical capacity, and perceptions of physical functioning across different populations and research settings.20) It is particularly crucial to assess functional capacity in hypertensive patients to estimate functional consequences and disability. While previous studies21) have confirmed the accuracy of the 2MST as a tool for evaluating the functional capacity of older individuals with hypertension, there is still a research gap in comparing the 2MST with other conventional functional measures in this specific population. Additionally, the correlation between the 2MST and other physical fitness tests remains unexplored. Therefore, the present study aims to investigate the predictive ability of the 2MST in identifying functional impairment in hypertensive older adults and its correlation with other functional measures, including the 6MWT, FTSST, TUG, grip strength, and leg strength.
MATERIALS AND METHODS
Participants
A cross-sectional study was conducted on 91 hypertensive older individuals in Phayao Province, Thailand, who were undergoing routine antihypertensive medication therapy. The eligible participants were identified and recruited during their routine appointments at a primary healthcare center, and informed consent was obtained from all individuals prior to their participation. The study included participants who met specific criteria, including a diagnosis of hypertension, age >60 years, a body mass index (BMI) <30 kg/m2, and the absence of any physical limitations that would impact their ability to walk or perform stepping movements. Participants with respiratory diseases or clinical conditions such as cognitive impairment, uncontrolled hypertension, unstable angina, and infectious diseases were excluded from the study. The study was approved by the Human Research Ethics Committee of the University of Phayao (No.1.2/056/65). The minimum sample size required was estimated to be 62 participants for a diagnostic study with a power of test set at 90%, a p-value at 0.05, and sensitivity taken from a previous study21) at 80%.
This study complied the ethical guidelines for authorship and publishing in the Annals of Geriatric Medicine and Research.22)
Procedure
The experimental protocols consisted of two separate visits. During the first visit, participants' general information was collected through a questionnaire, including sociodemographic variables such as age and sex, as well as anthropometric measurements such as height and weight for calculating body mass index (BMI) and general clinical data—duration of hypertension, medical conditions, physical activity by Physical Activity Questionnaire for Elderly Japanese23)—were collected. Subsequently, a physical fitness test, a handgrip strength, leg strength, TUG, FTSST, and 2MST were measured in each participant with a 30-minute rest between tests. Later the following week, participants were performed a 6MWT.
Hand grip strength was assessed using a hand dynamometer (Takei Scientific Instruments Co. Ltd., Tokyo, Japan). Participants completed a practice test and then performed three trials, exerting maximum force for 3 seconds with their dominant arm. Average values were recorded based on the three trials.24)
During the leg strength protocol, participants positioned themselves on the dynamometer base with feet shoulder-width apart. Using the back and leg dynamometer (Takei Scientific Instruments Co. Ltd.), they firmly grasped a bar and the chain was adjusted to flex their knees at around 110°. They were then instructed to exert maximum effort by pulling forcefully on the chain, aiming to straighten their legs and maintain straight upper limbs without flexing their back. Each subject completed two trials, and their highest performance was recorded.25)
The TUG protocol times subjects as they rise from a chair, walk to a line 3 m away, turn, walk back, and sit down. They have one practice walk-through, using a chair with a seat height of approximately 46 cm. Three attempts are made with 1-minute rest intervals and verbal encouragement, recording the quickest time for analysis.26) This is a reliable and valid assessment designed to measure basic functional mobility in older individuals.27,28)
The FTSST protocol, participants were asked to stand up and sit down as fast as possible with their arms folded across their chest for five times. Two trials were conducted with a rest of 1 minute in between. The average time of the two trials was recorded as the test result.29) The FTSST is proven to be a reliable and effective assessment tool for evaluating dynamic balance and functional mobility among older adults.30)
The 2MST protocol, participants were instructed to stand against a wall and a mark was made on the wall at the level of the anterior superior iliac crest and patella. Half the distance between the two marks was then marked using a piece of tape. Participants were asked to lift their knees to the height marked by the tape while treading in place as quickly as possible for 2 minutes. The number of steps taken on the right side, reaching the criterion height, was counted for each subject as the test record.20) The test exhibited good test-retest reliability (intraclass correlation coefficient=0.90) and demonstrated convergent validity (r=0.73) with 1-mile walk time for adults aged 60–94 years old.17,20)
In the 6MWT protocol, participants first record vital signs, dyspnea, and leg fatigue after a 5-minute rest period. They are then instructed to briskly walk for 6 minutes without running or stopping, along a straight and measured corridor or track typically spanning 30 m. Subjects are encouraged to cover as much distance as possible within the allocated time while refraining from running. The distance covered during the test is recorded.14) The 6MWT demonstrated good test-retest reliability and convergent validity with treadmill performance in older adults.31)
Statistical Analysis
The normality of the data distribution was assessed using the Shapiro–Wilk test. Descriptive statistics including means, standard deviations, and percentages were computed for participant characteristics and the outcomes of the study. Receiver operating characteristic curve analysis was used to identify the accuracy of the 2MST in differentiating between hypertensive older adults with or without functional impairment. We used cutoff of the 6MWT (320 m)18) known to be associated with low exercise endurance in elderly. Based on these cutoffs, a threshold for the 2MST was determined to identify functional impairment. The values of the area under the curve (AUC), the best cutoff point, sensitivity and specificity were identified. Hypertensive older individuals below or above the cutoff point in the 2MST were compared using independent samples t-test or Mann-Whitney U test when appropriate. Physiological responses—blood pressure (BP), heart rate (HR), and oxygen saturation (O2 sat)—and differences between the 2MST and 6MWT were evaluated using dependent samples t-test or signed-rank test. Leg fatigue and dyspnea scores were measured using the signed-rank test. The Pearson correlation coefficient was used to verify the correlation between the 2MST and 6MWT, handgrip strength, leg strength, TUG, FTSST, and 6MWT. Data were analyzed using the Stata 14.0 (StataCorp LLC, College Station, TX, USA), with a significance level of 5%.
RESULTS
The study enrolled 91 hypertensive older individuals, with a mean age of 70.29±4.95 years and an almost equal distribution of males (49.45%) and females (50.55%). The participants had a mean body weight of 58.59±0.71 kg, a mean height of 160.94±12.02 cm, and a mean BMI of 22.59±3.85 kg/m2. The mean systolic blood pressure (SBP) was 135.91±16.55 mmHg, while the mean diastolic blood pressure (DBP) was 73.31±9.20 mmHg. The average duration of hypertension diagnosis was 8.87±3.54 years, and most participants had comorbidities including diabetes (48.4%), dyslipidemia (38.46%), and orthopedic problems (9.89%). A small proportion of participants had cardiovascular disease (8.79%). The participants’ level of physical activity was 8.77±5.23 metabolic equivalents (METs) hr/wk, indicating moderate physical activity levels. Table 1 summarizes the characteristics of the participants.
The results in Table 2 demonstrate that the 2MST has an optimal cutoff score of ≤60 steps, with a sensitivity of 87.50% and a specificity of 70.59%. The AUC was 0.91 (95% confidence interval, 0.84–0.97).
The group that completed the 2MST in <60 steps had significantly lower handgrip strength, leg strength, TUG, FTSST, and 6MWT distances than the group that completed it in ≥60 steps (p<0.001). The group that completed the 2MST in <60 steps also had significantly lower SBP and higher DBP than the other group (p<0.001 and p=0.036, respectively). There were no significant differences between the two groups in HR, HR as a percentage of predicted maximum, O2 sat, and dyspnea grade (p>0.05) (Table 3).
Table 4 shows the results of the comparison of physiological responses, dyspnea, and leg fatigue between the 2MST and 6MWT in older adults with hypertension. The results show that the HR in beats per minute (bpm) during the 2MST was significantly increased when compared to the 6MWT (86.91±14.10 bpm vs. 83.02±15.36 bpm; p<0.001), as well as the HR in percentage of predicted maximum HR (57.10%±2.56% vs. 54.69%±2.20%; p<0.001). SBP during the 2MST was also significantly higher than that during the 6MWT (154.33±21.61 mmHg vs. 144.42±18.71 mmHg; p<0.001). There was no significant difference in DBP and O2 sat between the two tests (p=0.452 and p=0.050, respectively).
Regarding the subjective responses, the dyspnea level during the 2MST was significantly higher than during the 6MWT (11.48±2.73 vs. 10.54±2.92, p=0.004), while the leg fatigue level during the 2MST was significantly higher than during the 6MWT (2.12±1.67 vs. 1.45±1.33, p<0.001) (Table 4).
Table 5 presents the associations between the number of steps in the 2MST and various demographic and physical factors in hypertensive older adults. The results demonstrate a negative correlation between the 2MST and age (r=-0.294, p=0.005), a positive correlation with height (r=0.332, p=0.001), but no significant correlation with body weight (r=0.144, p=0.172).
The study also measured several physical fitness tests in the same population, including the distance of the 6MWT, grip strength, leg strength, duration of TUG, and duration of FTSST. The results show that the number of steps in the 2MST is positively associated with the distance of the 6MWT (r=0.747, p<0.0001), isometric grip strength (r=0.567, p<0.0001), and isometric leg strength (r=0.472, p<0.0001). In contrast, the number of steps in the 2MST is negatively associated with the duration of the FTSST (r=-0.491, p<0.0001) and the duration of the TUG (r=-0.632, p<0.0001) (Table 5).
DISCUSSION
The study investigated the usefulness of the 2MST in assessing functional fitness in hypertensive older individuals and its correlation with other physical fitness tests. The findings demonstrated that the 2MST is an effective tool for identifying functional limitations in this population, with a cutoff score of ≤60 steps indicating lower functional ability and physiological responses. Additionally, the 2MST was found to be more challenging than 6MWT and showed significant correlations with demographic factors, handgrip strength, leg strength, TUG, and FTSST.
The 2MST, originally part of the Senior Fitness Test developed by Rikli and Jones16) in 1999, is specifically designed to assess aerobic endurance and lower body strength in older adults. Previous studies have demonstrated the usefulness of the 2MST in evaluating functional capacity and have shown it to be a reliable and valid measure of physical fitness in older.13,17,20,21)
In this study, the cutoff score of ≤60 steps in the 2MST accurately identified individuals with lower functional ability and effectively differentiated older individuals with hypertension and without functional impairment, with a sensitivity of 87.50% and specificity of 70.59%. The high AUC value of 0.91 suggests that the 2MST has a strong overall accuracy in predicting functional impairment. These findings are consistent with those of previous studies that examined cutoff values for identifying impaired functional status. In a study conducted by Guedes et al.,21) they investigated the use of the 2MST to determine impaired functional status in individuals with hypertension and individuals who have hypertension and other associated chronic conditions (ACC). The study demonstrated that performing below certain repetition thresholds (<69 steps for hypertension and <65 steps for ACC) indicated reduced functional capacity. Sensitivity and specificity values further validated these findings, while the calculated AUC values (0.7 and 0.88) indicated a moderate to high level of accuracy in predicting reduced functional capacity. This study supports the 2MST as a valuable tool for identifying impaired functional status, offering a practical and useful clinical assessment for evaluating functional capacity and guiding interventions
Our sub-groups analysis revealed that cutoff values of 2MST provide a significant finding for functional fitness in individuals with hypertension. Performing <60 repetitions in the 2MST was associated with longer times on the timed TUG test and FTSST, indicating potential mobility and balance issues. These findings, along with lower handgrip and leg strength and higher levels of leg fatigue, suggested a decrease in overall physical fitness, including reduced endurance and physical capacity. Therefore, having <60 repetitions in the 2MST may serve as a useful marker to identify functional impairment and indicate the need for interventions to improve physical fitness and functional capacity in individuals with hypertension.
The 2MST is a good measure of cardiorespiratory fitness when other submaximal fitness tests could not be undertaken, such as the 6MWT, involves lifting the knees to the mid-level between the patella and iliac crest,7) which requires more intensity and longer duration of single-leg support than the standard step.32) In our study with hypertensive older adults, we found that the 2MST elicited a higher HR, SBP, dyspnea, and leg fatigue compared to the 6MWT. The biomechanics of the 2MST require greater lower-body strength, physical skills, and longer periods of single-leg support,33,34) explaining the higher physiological demand and RPE compared to the 6MWT. RPE was significantly higher in the 2MST compared to the 6MWT.
The 2MST and 6MWT show a correlation, suggesting that both tests are reliable indicators of cardiorespiratory fitness.13,19) Our study’s results are consistent with previous research, which suggests that the 2MST can complement the 6MWT in various populations, including those with coronary artery disease,35) hypertension in older adults,13) symptomatic peripheral artery disease,36) and systolic heart failure.37) Additionally, other studies have reported an association between these tests in both healthy older individuals7) and those with pathologies,13,19,37) suggesting that the 2MST can assess the integrated global response to exercise of all human body systems. It is worth noting that our study found correlations between age, height, weight, and the 2MST, which suggests that these factors may impact test performance and should be taken into consideration.
Our study revealed a significant inverse correlation between the 2MST and two functional mobility tests, FTSST and TUG, which assess the ability to complete tasks such as standing up from a chair or standing on one leg. These results reinforce the strong relationship between cardiovascular endurance and functional mobility. A negative correlation implies that poor cardiovascular endurance may lead to poor functional mobility and vice versa. These results are consistent with previous studies that have reported a correlation between functional capacity and functional mobility in older adults with hypertension.12,13) Moreover, our study found a significant positive correlation between the 2MST and handgrip and leg strength. This supports prior research indicating a relationship between the 2MST and quadriceps strength in patients with systolic heart failure.37) In older adults, maintaining strong handgrip and leg muscles is crucial for not only completing daily tasks but also for reducing the risk of mortality, functional decline, disability, and falls, as supported by previous research.10,38,39) Moreover, poor aerobic endurance and leg strength are significant contributors to slow gait velocity in community-dwelling stroke patients.40)
It is important to acknowledge the limitations of this study. Firstly, potential confounding factors such as sex, medical conditions, medication use, and orthopedic problems may have influenced the findings but were not fully controlled. To strengthen the validity of the findings, future research should aim to address these factors. Secondly, the study did not specifically examine the test-retest reliability of the 2MST in hypertensive older adults, which is essential for understanding its consistency and enhancing its validity. Additionally, the validity of the 2MST with respect to sex was not analyzed, and establishing cutoff points or categories for clinical support was not feasible. Therefore, further research is recommended to address these gaps and gain a more comprehensive understanding of the validity of the 2MST
In conclusion, the 2MST demonstrates effectiveness in identifying functional limitations and physiological responses in older individuals with hypertension, where a cutoff of <60 steps indicates lower functional ability and physiological responses. Additionally, the 2MST shows correlations with the 6MWT, grip strength, leg strength, FTSST, and TUG duration. Moreover, the 2MST is a validated, efficient, and cost-effective method for assessing functional disabilities in older individuals with hypertension, including those with comorbidities. Consequently, the 2MST holds substantial value in clinical outpatient and primary healthcare settings
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