Fitness as a determinant of the oxygen uptake/work rate slope in healthy children and children with inflammatory myopathy.

Abstract

There is evidence that the slope of the change in oxygen uptake accompanying changes in work rate (delta VO2/delta W). during moderate incremental exercise is influenced by fitness (peak VO2). We set out to determine whether delta VO2/delta W was related to fitness in a group of healthy children and in children with juvenile dermatomyositis (JDM), a condition associated with decreased peak VO2. We also hypothesized that delta VO2/delta would be significantly decreased in children with JDM compared to healthy children. Twelve children (2 boys) with JDM, mean age 11.6 +/- 3.6 yrs, and 20 healthy children (4 boys), mean age 11.3 +/- 2.9 years, performed an incremental exercise test using a cycle ergometer. delta VO2/delta W below the anaerobic threshold was analyzed using linear regression. Correlations between peak VO2 and delta VO2/delta W were calculated, and differences between the JDM and healthy groups were analyzed using independent t-tests. The delta VO2/delta W was significantly correlated with peak VO2 for children with JDM (r = 0.71, p < 0.01), healthy children (r = 0.53, p < 0.01), and all children combined (r = 0.78, p < 0.001). The delta VO2/delta W (7.4 +/- 1.4 vs. 10.8 +/- 1.2 ml O2.min-1.watt-1) and peak oxygen uptake (VO2peak) (19.2 +/- 5.0 vs. 31.4 +/- 7.2 ml O2.kg-1, min-1) were significantly lower in children with JDM than in healthy children, respectively (all p < or = 0.001). Fitness is significantly related to delta VO2/delta W in healthy children and those with JDM. Children with JDM have a significantly lower delta VO2/delta W than healthy children. Further study is needed to identify specific factors influencing delta VO2/delta W.