Sensitivity to change of aerobic exercise parameters in children with juvenile myositis

Juvenile myositis (JM) is a rare disease in which the immune system targets the microvasculature of the skeletal muscle and skin, leading to significant muscle weakness and exercise intolerance. 
PURPOSE: To investigate the changes in aerobic exercise parameters in children with JM during an active and inactive disease (remission) period, and secondly to study the sensitivity to change of these exercise parameters.
METHODS: 13 children with JM (mean±SD age: 11.2±2.6 years) participated in this study. Subjects performed a maximal exercise test using an electronically braked cycle ergometer and a calibrated respiratory gas analysis system (Jaeger Oxycon Pro). Exercise parameters that were measured and derived included: peak oxygen uptake (VO2peak), peak work rate (Wpeak), peak heart rate (HRpeak), and ventilatory anaerobic threshold (VAT). All children were tested during an active period of the disease as well as during a remission period. From these data four different responsiveness statistics were calculated: standardized response mean (SRM), Cohen's effect size (ES), paired t-tests and % change from baseline.
RESULTS: The children performed significantly better during the remission period compared to a period of active disease (see Table 1). Most exercise parameters showed a very large responsiveness (ES > 0.8)
CONCLUSION: We found that children with JM during the active disease phase had significantly reduced exercise parameters compared to a remission period. The physiological variables were not as sensitive to change compared to work rate. This suggests some type of metabolic disconnection, which might be caused by the reduced blood flow to the active musculature.