Alteration of Lactate Production During Incremental Exercise in Myotonic Dystrophy Is Not Dependent by Catecholamine Increase

Abstract

Abnormalities of mitochondria have been reported in Myotonic Dystrophy (MD). Adrenergic activation is one of the major factors influencing exercise lactate production in healthy subjects. In order to assess the role of such activation in MD, we compared blood catecholamine levels to those of lactate during an incremental bicycle exercise in 9 MD patients and 6 controls. The lactate values reached significantly higher levels in patients than in controls at rest (2.91 ± 0.58 vs 1.44 ± 1.14 mmol/l, p<0.01, in average), at the anaerobic threshold (4.43 ± 1.11 vs 2.62 ± 0.73 mmol/l, p<0.05), at exercise peak (6.64 ± 1.34 vs 3.90 ± 0.99 mmol/l, p< 0.05) and at recovery (3.21 ± 0.94 vs 1.91 ± 0.19, p<0.01). Furthermore, the anaerobic lactate threshold (LT) in MD was acquired at lower workload (mostly in a range between 30 % and 50 % of the predicted normal maximal power output) compared to controls (60-70%), this suggesting an early activation of the anaerobic metabolism in MD patients. On the contrary, catecholamine levels were not significantly different between patients and controls. These results indicate that abnormal lactate production in MD is independent of the adrenergic response to exercise and suggest a direct involvement of skeletal muscle o-xidative metabolism in MD