GREATER PERIPHERAL THAN CENTRAL ADAPTATION TO AEROBIC TRAINING IN MITOCHONDRIAL MYOPATHIES 186

Abstract

In theory, limited aerobic capacity in patients with mitochondrial myopathies (MM) could be secondary to the primary disease process or effects of chronic deconditioning. The objectives of this study were to determine 1) whether patients with MM could respond to aerobic training and 2) their ability to adapt centrally versus peripherally relative to patients with other chronic non-metabolic myopathies (NM). 10 patients with MM, 6 patients with NM, and 5 sedentary healthy control subjects were evaluated before and after undergoing a similar aerobic training regimen for 8 weeks. Aerobic capacity(METs) was estimated from performance on a graded exercise test to 85% HRmax. Heart rate for an identical submaximal exercise workload was used as an index of central adaptation. Blood lactate at rest and after a constant submaximal workload, and muscle oxidative ATP resynthesis after ischemic exercise (as reflected by the ADP recovery half time [T1/2] estimated by phosphorus magnetic resonance spectroscopy) were used as indices of peripheral muscle oxidative capacity. The mean initial fitness level was similar in MM and NM, and significantly lower than that of healthy controls(p<.01). Training resulted in a significant improvement in aerobic capacity in all groups, but MM improved 20% more than NM and 27% more than controls. Decreases in HR were detected in both patient groups (p<.01) but only MM showed significant improvement (p<.01) in blood lactate concentrations(50%) and ADP T1/2 (over 2-fold) after training. Thus, both MM and NM benefit from aerobic training, but MM benefit even more than NM. The difference appears to be due to greater peripheral adaptation in MM and supports the hypothesis that partially reversible limitation at the muscle level dominates the training response in patients with mitochondrial myopathy.