Cycle ergometry is not a sensitive diagnostic test for mitochondrial myopathy

Cycle exercise has repeatedly been used to diagnose patients suspected of having mitochondrial myopathy (MM), in whom exercise intolerance and lactic acidosis are common. No standardized test, however, has been established. We evaluated the diagnostic value of incremental and constant workload (20 min at 65 % VO2max) cycle tests for the diagnosis of MM. Plasma lactate and oxidative capacity (VO2 and workload) were measured in 15 well-characterized MM patients during cycling. Findings were compared with those in 10 myotonic dystrophy patients and 18 sedentary, healthy subjects.