A comparison of new cardiovascular endurance test using the 2-minute marching test vs. 6-minute walk test in healthy volunteers: A crossover randomized controlled trial

This was a 2×2 randomized crossover control trial to compare the cardiovascular endurance of healthy volunteers using a 2-minute marching test (2MMT) and a 6-minute walk test (6MWT). This study included 254 participants of both sexes, aged 20–50 years, with a height and body mass index (BMI) of ≥150 cm and ≤25 kg/m2, respectively. Participants could perform activities independently and had normal annual chest radiographs and electrocardiograms. A group-randomized design was used to assign participants to Sequence 1 (AB) or 2 (BA). The tests were conducted over 2 consecutive days, with a 1-day washout period. On day 1, the participants randomly underwent either a 6MWT or 2MMT in a single-anonymized setup, and on day 2, the tests were performed in reverse order. We analyzed maximal oxygen consumption (VO2max) as the primary outcome and heart rate (HR), respiratory rate (RR), blood pressure (BP), oxygen saturation, dyspnea, and leg fatigue as secondary outcomes. Data were collected from 127 participants, categorized into two groups for different testing sequences. The first (AB) and second groups had 63 and 64 participants, respectively. The estimated VO2max was equivalent between both groups. The 2MMT and 6MWT estimated VO2max with a mean of 41.00 ± 3.95 mL/kg/min and 40.65 ± 3.98 mL/kg/min, respectively. The mean difference was -0.35 mL/kg/min (95% confidence interval: -1.09 to 0.38; p <0.001), and no treatment and carryover effects were observed. No significant changes were observed in HR, RR, and systolic BP (p = 0.295, p = 0.361 and p = 0.389, respectively). However, significant changes were found in the ratings of perceived exertion (p <0.001) and leg fatigue scale (p <0.001). The 2MMT is practical, simple, and equivalent to the 6MWT in estimating VO2max.

Methods
Sample size

The sample size required for the equivalence study was estimated using nQuery software and calculated using two one-sided equivalence tests for crossover design. To calculate the sample size, we set the alpha error probability, statistical power, the lower equivalence limit, and upper equivalence limit at 5%, 90%, -2.00, and +2.00, respectively, using the clinical margin (minimal clinically important difference [MCID] of VO2max from a previous study, which was 2 ml/kg/min [15], and standard deviation was 8.6 [16]. Based on these values, we needed 101 participants for the crossover design, allowing for a 20% dropout rate. Therefore, we decided to randomize 127 patients per arm, resulting in 254 participants. However, due to the COVID-19 pandemic, data collection was incomplete, and we could only analyze 127 data sets in this study.

Inclusion and exclusion criteria

The inclusion criteria were male and female healthy volunteers, aged 20–50 years, with height: ≥150 cm and, BMI ≤25 kg/m2. Participants could perform activities independently and had normal annual chest radiographs and electrocardiograms. The exclusion criteria were significantly unstable vital signs, a history of COVID-19, and underlying heart disease or neuromuscular/skeletal impairment.

Procedure and measurement

We conducted a 2MMT and compared the results with those of the standard test, the 6MWT, to test the equivalence of both tests in estimating VO2max

Condition A: According to the standard protocol, the 6MWT was performed indoors on a flat surface in a 30-m straight corridor, with 180º turns every 30 m. [10]. The walk test was performed with stable vital signs, and SpO2 was maintained at >95%, all monitored by a cardiopulmonary physical therapist.

Condition B: The 2MMT was developed to determine the number of steps performed within 2 min. After the “start” command, the participants began marching in place and lifting their knees to an appropriate height of 30 cm. The participants were instructed to perform as many steps as possible (reaching a height of 30 cm) within 2 min. The participants were allowed to perform a few training steps to adjust to the marching technique and verify their ability to complete the task. The participants marched at their own pace; they could slow down or even stop, if necessary, and continue marching until the end of the 2-minute test period. The investigator determined the number of steps performed, informed the participants about the time left until the end of the trial, and motivated them to achieve the best possible result. The test results were expressed as the number of performed steps during which the right foot touched the ground.

When the participants exhibited severe symptoms of exercise intolerance in both tests, such as severe dyspnea, fatigue, or other alarming symptoms, they were allowed to slow down or stop and rest. However, they were encouraged to resume the test as soon as possible. Adverse events were monitored during and after test completion. Both tests were terminated and interpreted as incomplete if any of the following symptoms were present: chest pain, intolerable dyspnea, leg cramps, staggering, diaphoresis, and ashen appearance.

Data regarding the sex, age, BMI, HR, and RR were collected, and SpO2 was assessed using the NONIN Onyx2 9590 Oximeter, SBP and DBP were measured using the Philip Patient Monitor Efficia CM100, RPE, and LFS were assessed using the Borg’s scale. All parameters were recorded at 1 min, 5 min, and 10 min for pretest and posttest.

VO2max estimated the cardiovascular endurance using the following formula:

VO2max estimated in the 6MWT: 70.161 + (0.023 × 6MWT [m]) - (0.276 × weight [kg]) - (6.79 × sex, where m = 0, f = 1) - (0.193 × resting HR [beats per minute] - (0.191 × age [years]) [15]. where resting HR is the 10-min resting HR of posttest.

VO2max estimated in the 2MMT: 13.341 + 0.138 × total up and down steps (UDS) – (0.183 × BMI) [16].

Data analysis

Due to the COVID-19 pandemic in Thailand and hospital policies, only 127 of the 254 participants, who were healthy volunteers, could complete data collection. Descriptive statistics were used to evaluate demographic characteristics. Continuous variables were reported as mean ± standard deviation, whereas binary variables were reported as percentages. The primary outcome (VO2max), evaluated using Statgraphics software, was analyzed through a two-one-sided t-test procedure. The analysis was conducted with an equivalence bound of ± 2 mL/kg/min from the margin of VO2max observed in a previous study [17]. The carryover and treatment effects were insignificant, and the equivalence result was significant for the test. For the secondary outcome, all parameters were analyzed using a linear mixed-effect model to compare 2MMT and 6MWT with STATA software.

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