Validity of the 6‐minute walking test in juvenile idiopathic arthritis

Lower physical activity levels and decreased physical fitness levels have been reported in children with juvenile idiopathic arthritis (JIA) (1). Physical fitness includes 4 components: muscular endurance and strength, flexibility, body composition, and cardiorespiratory endurance or aerobic fitness (2). Cardiorespiratory endurance or aerobic fitness is most strongly associated with health benefits in the general population and is therefore the primary focus of most exercise programs (3,4). Children with JIA have a moderate to large impairment in aerobic fitness as represented by peak oxygen uptake (VO2peak) compared with healthy children (5). VO2peak has been described as the golden standard for aerobic fitness and is frequently examined using symptom limited bicycle ergometry (SLBE) in combination with a metabolic cart to analyze respiratory gases (6). However, bicycle ergometry and metabolic measurements are not always feasible in pediatric patients. It may be difficult to motivate nonathletic children to an exhaustive effort, intensive exercise may pose a risk to children with cardiopulmonary or musculoskeletal disease, and metabolic measurements systems may not be available, particularly in a field setting (7). Therefore, there is need for simple and inexpensive measurement tools to measure aerobic fitness. The 6-Minute Walking Test (6MWT), a simple and inexpensive measurement tool, is a good candidate (8). The 6-MWT is a self-paced and submaximal endurance test. In adult patients the 6-MWT has been widely used, most often in patients with pulmonary or cardiac diseases (9,10). Literature provides support for the reliability, validity, and responsiveness of the 6-MWT for a wide spectrum of adult individuals (9). In addition, the 6-MWT is described as easy to administer, better tolerated, and more reflective of activities of daily living than other walking tests and has therefore been described as the test of choice when using a functional walk test for clinical or research purposes (10). In pediatric patients, only 2 studies report the use of the 6-MWT (11,12). Gulmans et al found that for this group the 6-MWT is a valid and useful test to assess the exercise tolerance and endurance in children with cystic fibrosis (11). Nixon et al suggested that the 6-MWT might provide an alternative method for assessing functional exercise capacity in severely ill children (12). Despite these promising results, the validity of the 6-MWT in children with rheumatic disease has, to our knowledge, never before been examined. Validity refers to the question as to whether an instrument appears to measure what it purports to measure, i.e., endurance. In addition, validity indicates whether a variable can be correlated with the “gold standard” for cardiorespiratory endurance, i.e., VO2peak. The aim of the present study was to examine the validity of the 6-MWT in children with JIA.