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 Table of Contents  
ORIGINAL ARTICLE
Year : 2022  |  Volume : 11  |  Issue : 1  |  Page : 35-38

Reference equations for two-minute walk test in healthy Indian adults


Department of Physiotherapy, Mahatma Gandhi Mission's College of Physiotherapy, Navi Mumbai, Maharashtra, India

Date of Submission27-Oct-2021
Date of Decision07-Nov-2021
Date of Acceptance25-Nov-2021
Date of Web Publication04-Jan-2022

Correspondence Address:
Dr. Prachita Pravin Walankar
Mahatma Gandhi Mission's College of Physiotherapy, Plot No. 46, Sector-30, Vashi, Navi Mumbai - 400 705, Maharashtra
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/ijrc.ijrc_133_21

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  Abstract 


Introduction: Two-minute walk test (2MWT) is used widely to determine the functional capacity in clinical setup. However, reference equations derived from Western population cannot be applied to Indian subjects owing to the ethnic differences. Hence, the current study aimed to establish reference equation for 2MWT in healthy Indian population. Subjects and Methods: A cross-sectional study was conducted in 480 healthy participants in the age group of 20–80 years who performed two 2MWTs using a standardized protocol. The highest value of two-minute walk distance (2MWD) was selected for further analysis. Results: The mean value of 2MWD was 152.33 ± 26.56 m. 2MWD for men (157.3 ± 23.82 m) was higher than females (147.35 ± 28.21 m) (P < 0.001). Bivariate analysis showed that 2MWD correlated significantly (P < 0.05) with age, height, and weight in both genders. Further, stepwise multiple linear regression analysis was performed to generate gender-specific reference equations using age, height, and weight as predictors of 2MWD. Conclusion: We established a gender-specific prediction equation for 2MWD in healthy Indian subjects. It can be used as a reference to interpret functional capacity in patients with acute illness, cardiorespiratory disease, and other health-related conditions.

Keywords: Functional capacity, India, reference values, two-minute walk test


How to cite this article:
Walankar PP, Tare R G. Reference equations for two-minute walk test in healthy Indian adults. Indian J Respir Care 2022;11:35-8

How to cite this URL:
Walankar PP, Tare R G. Reference equations for two-minute walk test in healthy Indian adults. Indian J Respir Care [serial online] 2022 [cited 2022 Jan 26];11:35-8. Available from: http://www.ijrc.in/text.asp?2022/11/1/35/334815




  Introduction Top


Walking tests document the distance walked over a defined period of time. It is used to characterize the functional capacity and endurance in research and clinical practice settings.[1] These are simple, safe, and inexpensive tests. There are varied walk tests available in literature-2, 6, and 12-min walk tests. It has been reported that, when these three well-known walk tests are compared with each other in respiratory conditions, it has been proven that, with respect to distance walked and maximal oxygen consumption, there is good correlation and high reliability among the three tests.[2]

Six-minute walk test (6MWT) is most frequently used walk test.[1],[2],[3] However, performance of 6MWT was found to be difficult, time consuming, and fatiguing in early postoperative patients, acute rehabilitation phase, severe disability, end-stage cardiorespiratory disease, and hospitalized patients.[4] In such scenario, two-minute walk test (2MWT) is being incorporated as an outcome measure for the assessment of functional capacity. It has been reported that 2MWT substantially correlates to 6MWT.[2],[5],[6] Literature reveals that 2MWT is used in varied conditions such as frail elderly, obesity, musculoskeletal conditions, recent cardiac surgeries, amputations, and neuromuscular diseases.[6],[7],[8],[9],[10]

The American Thoracic Society (ATS), which developed guidelines for the walking tests, emphasizes that specific reference values should be determined for different ethnicities and population globally.[3] Reference values and equations for the two-minute walk distance (2MWD) have been established for different populations across the globe which differ significantly.[11],[12],[13] However, these equations may not necessarily be applicable to Indian subjects. It has been reported in literature that the functional capacity of an individual depends on multiple factors such as genetics, body composition, environmental disparities, and ethnic differences.[14]

Literature shows that there is only one Indian cross-sectional study available that exhibits the reference values for 2MWT in healthy Indian adults.[15] However, heterogeneity and unequal distribution of subjects in the different age groups may affect the predicted distance in this study. Furthermore, reference equations for predicting the 2MWD were not established.[15] Hence, the primary aim of this study was to determine reference equations for 2MWD in healthy Indian adults aged 20–80 years.


  Subjects and Methods Top


A cross-sectional study using purposive sampling method was conducted between January and May 2021 after obtaining approval from the Institutional Research Review Committee. The sample size was determined using G * Power (version 3.1.9.3), with power of 90% and was estimated to 480 participants. They were equally divided into six groups. Each group had eighty subjects with forty males and forty females.

Inclusion criteria were healthy individuals in the age group of 20–80 years, both males and females, and willing to participate in the study. Exclusion criteria were body mass index (BMI) <18 kg/m2 or >30 kg/m2, hypertension, diabetes mellitus, cardiac conditions, pulmonary conditions, musculoskeletal problems such as osteoarthritis involving lower extremities interfering with the walking ability, any recent trauma or any surgery, neurological conditions, smokers, pregnant and lactating mothers, clinically diagnosed psychiatric disorders, subjects on any prolonged medications because of chronic diseases, any history of fall, and subjects using any walking aid and those involved in any formal, regular physical training or competitive sports. Participants were explained about the study in detail. A written informed consent was signed by those who were willing to participate in the study.

We studied 480 healthy subjects in the age group of 20–80 years. The subjects were stratified into the following six categories, based on age: 20–29 years, 30–39 years, 40–49 years, 50–59 years, 60–69 years, and 70–80 years.

Appropriate loose and comfortable attire and comfortable shoes for walking were recommended for all the participants. They were told to consume a light meal 2 h before testing. Demographic data of the participants were noted. Standardized measurement methods were employed to assess body weight (kg) and body height (cm). BMI was calculated using the standard formula (body mass (kg)/body height (m2).

Before starting the walk test, vital parameters such as heart rate beats per minute, blood pressure (mmHg), and peripheral arterial oxygen saturation (SpO2%) were measured in sitting position after resting for at least 5 min. The 2MWT, a modified version of 6MWT, was performed as per the standardized guidelines given by ATS.[3]

A 30-m long corridor was selected where participants were asked to walk back and forth on the marked course. They were instructed to walk as far as possible without running for a 2-min period. Based on the recommendations for the 6MWT, encouragement was given after the first minute with the following standardized phrases: “You're doing well” and “One minute left.” In case of any discomfort, they were permitted to slow down or take rest. Once they felt better, they were boosted to continue walking and complete the test. Participants stopped walking at 2 min, and the distance covered was documented as 2MWD. Directly after the test, heart rate, blood pressure, and SpO2% were re-measured. 2MWTs was performed twice by each subject with an interval of 2 h and was administered by the same investigator. The best of two trials was used for further analysis.

Statistical analysis

Data were analyzed using the Statistical Package for the Social Sciences (SPSS) version 24 software (IBM SPSS Statistics for Windows, Version 24.0. Armonk, New York, USA: IBM Corp. IBM Corp. Released 2016). Normality of data was assessed using Kolmogorov–Smirnov test. Data were normally distributed. Hence, parametric tests were used. Mean and standard deviation were used to express quantitative variables, whereas numbers and percentages were used for qualitative variables as. The comparison of 2MWD between the age groups was performed using analysis of variance test. The difference in 2MWD between males and females was evaluated using independent t-test. Pearson's correlation test was performed to assess correlation between 2MWD and age, height, weight, and BMI. Stepwise multiple regression analysis was performed to determine reference equations for 2MWD. Multicollinearity analysis was performed using variance inflation factors were used for. A P < 0.05 was considered statistically significant.


  Results Top


The baseline characteristics and 2MWD values of participants are shown in [Table 1]. The mean 2MWD during first trial and second trial was 150.23 ± 25.76 m and 151.35 ± 26.18 m, respectively. It showed that there was good reliability (intraclass correlation coefficient = 0.979).
Table 1: Characteristics and two-minute walk distance of participants

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The mean age of the sample was 49 ± 17.55 years. There were significant gender differences with respect to anthropometric characteristics; height and weight. Men reported to be taller and had greater weight as compared to women. The mean 2MWD for all participants was 152.33 ± 26.56 m. In males, the mean distance was 157.3 ± 23.82 m and 147.35 ± 28.21 m for females. The difference between men and women was statistically significant (P < 0.001).

Age- and gender-specific values of 2MWD are represented in [Table 2]. It was observed that there was statistically significant difference between males and females in all age groups except 20–30 years. Furthermore, significant difference was noted between age groups.
Table 2: Age- and gender-specific values of two-minute walk distance

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Bivariate analysis showed that 2MWD correlated significantly (P < 0.05) with age, height, and weight in both genders [Table 3].
Table 3: Correlations between the independent variables and two-minute walk distance using Pearson correlation test

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The variance inflation factor value was close to 1, suggesting no significant multicollinearity between variables. In the stepwise linear regression analysis, age and anthropometric traits – height and weight were selected as predictors of 2MWD. [Table 4] shows unstandardized beta coefficient and standard error of dependent variables among males and females.
Table 4: Stepwise multiple linear regression analysis of independent variables that explained two-minute walk distance

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The reference equations for 2MWD were as follows:

Males: 2MWD = 123.896 + (−1.293 × age) + (0.646 × height) + (−0.2 × weight)

Females: 2MWD = 186.624 + (−1.474 × age) + (0.322 × height) + (−0.314 × weight).


  Discussion Top


The present study provides reference values for 2MWT in healthy subjects between 20 and 80 years of age. It was observed that males walked a longer distance than females in all age groups. The difference observed in gender can be due to superior muscle strength, greater muscle mass, and higher height in men.[16]

Furthermore, association between independent variables such as age, height, and weight and dependent variable 2MWD was seen in both males and females. An inverse association was seen between 2MWD and age. Shorter distance was walked by elderly as compared to younger subjects. Reduction in muscle mass, muscle strength, and maximal oxygen uptake is seen as the age progresses.[17],[18],[19]

There was a significant positive correlation seen between height and distance. It implies that taller the individual, longer the stride taken, which increases the amount of distance walked. There was no association found with respect to BMI in males and females. This can be due to exclusion of overweight and underweight participants from our study.

Literature reports that demographic, anthropometric, nutrition, racial background, and lifestyle factors are varied in healthy subjects among different ethnic populations.[20],[21]

Hence, reference equations for 2MWD from western populations will not be applicable to Indians. The reference values may be useful to interpret 2MWT performance in patients with significant respiratory or cardiac dysfunction. This study will help physiotherapists to utilize 2MWT as an outcome measure in testing submaximal endurance of the patients in clinical settings. It can be used in the early stage of rehabilitation and acute illnesses to assess functional capacity of the patients. This test can also be used in a variety of health conditions including postcardiac surgeries, various pulmonary conditions, lower limb amputation, neuromuscular disease, and the elderly including those in long-term care.

Establishment of normative values for subjects aged <20 is necessary and is the future scope of this study. There are some limitations. We did not recruit underweight and obese people; our reference equations are not applicable to the subjects with 18< BMI >30 kg/m2.

To conclude this study established gender-specific reference equations for the prediction of 2MWD in healthy Indian subjects. This will facilitate to evaluate the functional capacity in patients with acute illness and cardiorespiratory conditions.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
  References Top

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Brooks D, Parsons J, Tran D, Jeng B, Gorczyca B, Newton J, et al. The two-minute walk test as a measure of functional capacity in cardiac surgery patients. Arch Phys Med Rehabil 2004;85:1525-30.  Back to cited text no. 7
    
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Reid L, Thomson P, Besemann M, Dudek N. Going places: Does the two-minute walk test predict the six-minute walk test in lower extremity amputees? J Rehabil Med 2015;47:256-61.  Back to cited text no. 10
    
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Casanova C, Celli BR, Barria P, Casas A, Cote C, de Torres JP, et al. The 6-min walk distance in healthy subjects: Reference standards from seven countries. Eur Respir J 2011;37:150-6.  Back to cited text no. 14
    
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Krishna Priya T, Verma S. A study to determine the reference values for two minute walk distance in healthy Indian adults. Int J Physiother Res 2015;3:1208-14.  Back to cited text no. 15
    
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Evans WJ, Campbell WW. Sarcopenia and age-related changes in body composition and functional capacity. J Nutr 1993;123:465-8.  Back to cited text no. 17
    
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Bemben MG. Age-related physiological alterations to muscles and joints and potential exercise interventions for their improvement. J Okla State Med Assoc 1999;92:13-20.  Back to cited text no. 18
    
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Deurenberg P, Deurenberg-Yap M, Guricci S. Asians are different from Caucasians and from each other in their body mass index/body fat per cent relationship. Obes Rev 2002;3:141-6.  Back to cited text no. 20
    
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Fischbacher CM, Hunt S, Alexander L. How physically active are South Asians in the United Kingdom? A literature review. J Public Health (Oxf) 2004;26:250-8.  Back to cited text no. 21
    



 
 
    Tables

  [Table 1], [Table 2], [Table 3], [Table 4]



 

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