Does the 6-min walk test correlate with the exercise stress test in children?

Is there a correlation between the 6-min walk and aerobic fitness in children? We studied healthy and cystic fibrosis (CF) subjects age 8-20 years using the 6-min walk test, treadmill graded exercise stress test, and spirometry. Six-minute walk distance (6MWD) and the product of 6MWD and body weight (6MWORK) were related to aerobic capacity. Data were analyzed using Student's t-test and Pearson correlation. 13 healthy subjects [9 females, mean age 15.8 +/- 3.6 years, % predicted forced expiratory volume in one second (FEV(1)) 105 +/- 12%, 6MWD 557 +/- 73 m, peak oxygen uptake (V' O2 max) 41.4 +/- 7.2 ml/kg/min, and heart rate (HR) at V' O2 max 180 +/- 10] and 11 CF subjects (3 females, mean age 14.3 +/- 3.8 years, FEV(1) 67 +/- 25.9%, 6MWD 468 +/- 68 m, V' O2 max 27.0 +/- 8.1 ml/kg, and HR at V' O2 max 163 +/- 22] were studied. 6MWD correlates with V' O2 max in normal subjects (r = 0.59, P < 0.05) but not in CF subjects (r = 0.09, NS). 6MWORK correlates with V' O2 max in CF subjects (r = 0.65, P < 0.05) but not in normal subjects (r = 0.278, NS). We conclude that the 6MWD corresponds with aerobic fitness in normal pediatric subjects and 6MWORK corresponds with aerobic fitness in CF subjects. We speculate that 6MWORK is superior to 6MWD for assessment of aerobic fitness in children with CF.