**3. A six-minute walk test on a special treadmill: Primary results in healthy volunteers**

The guidelines approved by the American Thoracic Society (ATS) in 2002 definitely recognize the six-minute walk test (6MWT) as a useful tool for the evaluation of physical efficiency in individuals with at least moderate chronic obstructive pulmonary disease, heart failure and intermittent dysbasia (ATS, 2002). In order to compare the results obtained in various research centres, the guidelines recommend that the test be performed in a hallway 30 m in length and at least 3 m in width. As a result, some centres without hallways of this area have a limited possibility of carrying out this simple test.

The authors of the ATS report appreciate the advantages of the 6MWT on a treadmill as it saves space and allows constant monitoring during the exercise.

So far, ATS has not approved the use of a treadmill to determine the six-minute walking distance (6MWD) because patients are unable to pace themselves on a treadmill. The divergence between the distances covered on the treadmill and in the hallway was pointed out. To support this point of view, a study of patients with severe lung disease was presented where the mean distance walked on the treadmill was shorter by 14% when compared with the standard 6MWD using a 30 m hallway (Stevens et al, 1999). In particular, doubts were expressed regarding the wide range of differences, with patients walking between 120÷390 m on the treadmill and 360 m in the hallway.

The popularity of the 6MWT in clinical practice (Montogomery & Gardnem, 1998; Roul et al., 1998; Zugck et al., 2000; Rostagno et al., 2003; Lipkin et al., 1986; Redelmeier et al., 1997), problems with the performance of the test on the treadmill and our first positive results with the use of a modified treadmill adapting to the pace of the patient's walk, encouraged us to check if our version of the algorithm enables healthy volunteers to cover a similar walking distance both on the treadmill and in the hallway.
