Effect of walkway length and turning direction on the distance covered in the 6-minute walk test among adults over 50 years of age: a cross-sectional study
Introduction
The 6-minute walk test (6MWT) is used to measure the maximum distance that a person can walk in 6 minutes. It was originally developed to assess cardiorespiratory [1] and cardiovascular endurance [2]. The distance covered during the 6MWT (6MWD) has been found to be significantly associated with peak oxygen uptake [3] and heart-failure-specific quality-of-life questionnaire scores [4]. It has also been shown to be a sensitive measure of the severity of heart disease, according to the New York Heart Association Functional Classification [2], [5], [6]. The 6MWD has been used to predict morbidity and mortality in patients with left ventricular dysfunction [5], advanced heart failure [3] and chronic obstructive lung disease [7].
In recent decades, the 6MWD has been validated as a general indicator of overall physical performance and mobility for older people [8], [9]. Performance of the 6MWT has been shown to improve after different types of intervention in older adults [10], [11], [12], patients with pulmonary hypertension [13], [14], patients with severe chronic obstructive pulmonary disease [15], and patients with neurological disorders including stroke [16], [17] and Parkinson's disease [18]. These studies found that the 6MWD was sensitive to change following an exercise intervention. The 6MWD is a useful instrument because it is easy to administer, similar to normal daily activities, and is well tolerated by elderly patients.
The reliability and validity of the 6MWT has been established with healthy older adults aged >65 years. Excellent test–retest reliability has been reported with intraclass correlation coefficients (ICCs) ranging from 0.91 to 0.96 [9], [19], [20], [21], [22] when comparing trials 2 days apart (ICC = 0.96) [19], 1 week apart (ICC = 0.91, ICC = 0.94) [9], [22], 2 weeks apart (ICC = 0.93) [20], and after resting until the heart rate has returned to the baseline level [22].
Although the 6MWT is commonly used as a submaximal test of aerobic capacity with older adults, the walkway length has not been standardised. According to the practical guidelines set by the American Thoracic Society [23], a standardised walking course must be 30 m in length. A 33-m walkway was initially adopted and used in some studies [2], [21], but different lengths including 100 feet [24], 15 m [25], 18 m [26], 30 m [19], [22], [27], [28] and 50 m [29] have been used in studies with older adults. Some studies have even used a circular walkway with a circumference of 40 feet [9], 121 m [30] or 185–397 feet [31]. As shorter walkways involve more turns to cover the same distance, the 6MWD might be affected by the length of the walkway.
Turning bias (i.e. the tendency to turn in a given direction) has been identified in healthy adults [33], [34]. Taylor et al. [32] showed a significant preference for turning towards the non-dominant side in 100 right-handed and right-footed adults. In a recent study of seven adults using an infra-red motion analysis system, Strike and Taylor [33] also found turning bias, which was significantly correlated with 11 of the 18 temporal–spatial gait variables measured: approach stride width, turn stride length, turn step length, turn velocity, depart stride length, depart step width, depart stride velocity, approach stride length, turn stance time, turn angle and anterior–posterior propulsive impulse. They found that the contributions to propulsion were significantly greater when turning away from the dominant leg [33]. Therefore, for the right-footed people, the desire was to support on the left (non-dominant) limb and propel from the right (dominant) limb [33]. No previous study has investigated the effect of turning direction on the results of a timed functional test (e.g. 6MWT).
It was hypothesised that walkway length and turning direction would affect the total 6MWD. This study was designed to investigate the effect of various walkway lengths and different turning directions on the 6MWT performance of community-dwelling older adults, as the 6MWT is a common test used to assess the walking endurance of elderly people.
Section snippets
Participants
This study had a cross-sectional design. A convenience sample of healthy adults aged ≥50 years (n = 25, aged 50 to 70 years) was recruited from a local community centre. The inclusion criteria were: (1) age ≥50 years, (2) able to walk 10 m with no physical assistance or walking aid, and (3) a stable general medical condition that would enable participation in the tests. Subjects were excluded if they had a disability that would hinder proper assessment.
The procedure was explained clearly to all
Results
The demographic characteristics of the subjects are shown in Table 1. Twenty-five subjects participated in the study and 48% were male. The mean age was 61 [standard deviation (SD) SD 8] years. The mean (SD) 6MWD and the mean (SD) number of turns are summarised in Table 2, Table 3.
Discussion
The main findings of this study were: (1) the length of the walkway has a significant effect on the 6MWD; and (2) turning direction does not have a significant effect on the 6MWD.
Conclusion
To the authors’ knowledge, this is the first study to investigate the relationship between walkway length, turning direction and 6MWD in elderly subjects. Turning direction was not found to have a significant effect on the 6MWD, but walkway length had the expected significant effect.
To produce reliable measurements of changes in functional capacity in older adults, it is recommended that a standard walkway length should be used, at least for the same patient when repeating the 6MWT in different
Acknowledgement
I would like to send my sincere thanks to Prof. Robert L. Kane, University of Minnesota School of Public Health, for his valuable guidance and advice in conducting clinical research, and to Dr. Raymond C.K. Chung for his statistical advice.
Ethical approval: The study was approved by the Ethical Review Board of Departmental Research Committee, Department of Rehabilitation Sciences, The Hong Kong Polytechnic University (no Reference number).
Funding: The Hong Kong Jockey Club Charities Trust
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