Überlagernde Nerv- oder Muskelstimulationen bieten eine Möglichkeit zur Aufdeckung von neuromuskulären Hemmungen. Mit der vorliegenden Studie sollte gezeigt werden, dass bei maximal willkürlichen Kontraktionen weder durch direkte (DST) noch durch indirekte (DST) überlagernde Muskelstimulation Kraftanstiege provoziert werden können. Bei 14 gesunden Probanden wurde die isometrische Maximalkraft der Kniestreckmuskulatur in vier verschiedenen Kniewinkelstellungen (45/60/75/90°) gemessen. Die Probanden befanden sich in Rückenlage (15° Hüftbeugewinkel). Während der maximal willkürlichen Kontraktionen wurde der M. quadrizeps femoris mit supramaximalen Einzelreizen (Rechteckimpuls, bipolar, 500 µs, 90 mA) direkt und indirekt stimuliert. Für die DST wurden Oberflächenelektroden (4 × 6 cm) über den M. vastus medialis, M. rectus femoris und M. vastus medialis verwendet. Die IST wurde mit einer bipolaren Elektrode in der Leistenbeuge über dem N. femoralis durchgeführt. Bei beiden Verfahren wurden in allen Kniewinkelstellungen im Mittel Kraftanstiege von weniger als 1 % gemessen. Weder für die verwendeten Stimulationstechniken noch für die verschiedenen Kniewinkel konnten signifikante Unterschiede ermittelt werden. Keine der beiden Techniken konnte bei gesunden Probanden Kraftanstiege über das willkürliche Maximalkraftniveau hinaus provozieren. Die Methode erscheint daher zur Aufdeckung von Rekrutierungshemmungen bei Patienten mit Verletzungen und Funktionsstörungen als geeignet.
Direct and indirect interpolated electric muscle stimulation to discover incomplete muscle activation
While superimposed twitch techniques offer a possibility for the detection of neuromuscular inhibitions it is still under controversial discussion whether healthy subjects can voluntarily achieve maximal recruitment of their knee extensor muscles. The goal of this study was to test the hypothesis that during maximal isometric contractions (MVC) neither direct (DST) nor indirect superimposed twitch techniques (IST) produce force increases. The isometric strength of the knee extensor muscles of both legs was measured in supine position (hip angle 15°) and different knee angles (45/60/75/90°) of 14 healthy subjects. The lower leg was fixed in a cuff connected to a force transducer. During MVC the quadriceps femoris was either directly or indirectly stimulated with supramaximal single pulses (rectangle, biphasic, 500 µs, 90 mA). For DST surface electrodes were fixed on the bellies of vastus medialis, vastus lateralis and rectus femoris referring to the motor points. The IST was conducted with a bipolar electrode over the femoral nerve in the groin. The order of stimulated leg, knee angle and stimulation technique was randomized. Both techniques revealed force increases smaller than 1 % in all knee angles. The Wilcoxon-test and the Quade-test did not reveal any significant differences for stimulation technique or knee angle. Apparently, both techniques do not generate force increases in healthy subjects. Thus, the method seems to be adequate for the detection of recruitment inhibitions in patients with functional disorders or injuries.
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