Análisis estructural

An alternative walk distance test is the 6 Minute Walk Test (6MWT). The 6MWT was developed in 1963 by Balke to evaluate functional capacity. The test measures the distance an individual is able to walk over a total of six minutes on a hard, flat surface. The primary outcome is the distance covered in metres or converted measure (such as feet) over 6 minutes. The further the distance covered indicates a greater function and ability of the participant to sustain cardiorespiratory workload (American Thoracic Society: Guidelines

for the 6MWT 2002). The 6MWT was also introduced as a functional fitness test by Lipkin to assess exercise capacity in chronic heart failure (Lipkin et al 1986). Peeters and Mets (1996) further extended the test by studying the appropriateness of the 6MWT on elderly patients with chronic heart failure. They compared the results of the 6MWT against the VO2max treadmill exercise test and concluded that whilst patients with chronic heart failure found it difficult to complete the VO2max test the 6MWT was better tolerated by elderly patients. Moreover, the results correlated well against the treadmill test. Thereafter, it was considered the test of choice and a reliable assessment to establish the exercise capacity of elderly patients with chronic heart failure and chronic obstructive pulmonary disease. In 1999 Trooster et al attempted to establish normal values for the 6MWT for healthy older people. They recruited 51 healthy volunteers aged 50-85 years. The tests were performed in a 50-metre long hospital corridor. Analysis of the data showed that age, height, sex and weight were independent contributions to the 6MWT in healthy subjects. Although the sample size was small and they showed a large variability, they concluded the 6MWT could be an adequate predictor of a healthy older person's exercise capacity at levels corresponding to their ADL's (Trooster et al 1999). Rikli and Jones (2001) extended the general acceptance of the 6MWT by incorporating the test in their screening procedure that precedes the start of the physical exercise programme in the senior fitness test manual.

Although the 6MWT has been widely accepted as an appropriate fitness test for older people it is important to note that there are variations among studies in how the test is conducted, which affects performance. The American Thoracic Society (ATS) guidelines 2002 emphasize that patients may become out of breath or exhausted and instructs them on taking rest breaks. In contrast, some articles instruct people to walk as quickly as possible for the full 6 minutes (Lord and Menz 2002). While many studies do not report the exact instructions, most describe the instruction as having participants walk at their usual pace or a comfortable pace and to walk as far as possible. The distance covered in six minutes in healthy adults has been reported to range

from 400 metres to 700 metres (Enright 2003). Age and sex-specific reference standards are available and may be helpful for interpreting 6MWT scores for both healthy adults and those with chronic diseases (Casanova et al 2011). An improvement of 54 metres has been shown to be a clinically important difference in healthy older adults (Redelmeier et al 1997). The minimal clinically important difference for patients with coronary disease after acute coronary syndrome is 25 metres (Gremeaux et al 2011). However, using normative values is problematic because of the differing methods used in studies. With such a range of instructions between studies and the need for a test to be carried out in the older person’s home, comparisons in the distance older people cover could be very diverse.

The 6MWT test requires a hard flat surface where the participant would not be interrupted or disturbed by other pedestrians (American Thoracic Society: Guidelines for the 6MWT 2002). Alternatively, if the test is undertaken outside or in a local sports centre some participants may feel conscious about performing the test in a public environment. The 6MWT also requires the participant to traverse back and forth along a marked course (American Thoracic Society: Guidelines for the 6MWT 2002). The ATS recommends an indoor, 30-metre corridor or walkway with cones placed at the beginning and end to indicate turns. However, across studies, the corridor distance varies which is likely due to the need to use readily available surroundings. Two studies have described how varying the distance between turning points to 10 or 20 metres resulted in the participant covering a shorter distance. Furthermore, although treadmills have been used to conduct the 6MWT, treadmills may underestimate total distance compared to the standard method done in a hallway or exercise room (Lenssen et al 2010 and Olper et al 2011). Marking out a distance in a participant’s home would doubtless be less than 10 metres and would therefore not be comparable in the distance covered by a participant who had a longer straight course. This would lead to inconsistencies in evaluating a participant’s ability against normative values. It is possible that for this reason the ATS suggests all tests should adhere to

For some older people just walking for 6 minutes could result in discomfort and pain. However, attempts to shorten the distance to 4 minutes has been found to be not as sensitive in assessing functional exercise capacity and the ability to engage in physically demanding activities of daily living (Strijbos et al 1996 & Du et al 2009). The accuracy and distance covered in the 6MWT could be dependent on the older person’s ability to pace themselves. Participants who start out too fast and subsequently have to slow down towards the end of the test because they are in pain or discomfort would not give an accurate indication of ability. Repeated tests could establish overtime a norm for every participant and would also allow for a learning effect. However, how many times the test would need to be repeated to determine the norm has not been established.

Motivation through verbal cuing may also lead to disparate results. High levels of encouragement and constant prompting may animate the participant to overreach their ability and wellbeing. As the 6MWT does not recommend any mechanism to monitor the older person's heart rate, there is no direct way of assessing if the participants safety is being compromised. By exceeding the predicted heart rate max; older people may put themselves at risk of over exertion.