[Fatigue at various muscular lengths in myotonic dystrophy]

In myotonic dystrophy alteration in membrane excitability characterizes, in addition to the dystrophic process, modifications of contractile function detectable after fatigue. To verify in which extent sarcolemmal activation or contractility mechanisms are involved in fatigue, some electrophysiological and dynamometer parameters have been studied in tibialis anterior of 5 myotonic dystrophy patients. Evaluation has been performed basally and after protocol consisting of intermittent isometric voluntary contractions lasting 15', at two different muscle lengths, optimal and short. Administration at several recovery times of 20 and 50 Hz tetanizing sequences shows how processes distal to membrane excitability are mainly responsible for fatigue at optimal length, while relative potentiation of excitability preserves the muscle from excessive force loss at short length.