The influence of increasing and decreasing frequency of stimulation on the contraction of motor units in rat medial gastrocnemius muscle.
Motoneurons during their activity can generate firings at changing rate. Therefore, the present paper aimed at studying the evoked contractions of different types of motor units to stimulation at progressively decreasing or increasing interpulse intervals. The influence of both patterns of stimulation on the tension, the duration and the tension-time area of motor units in rat medial gastrocnemius muscle was studied. The decreasing stimulation frequency resulted in generation of a bigger tension-time area although a slightly lower tension and a shorter duration of a contraction were observed in majority of studied units. For fast units a bigger tension-time area observed during the stimulation at decreasing frequency is probably due to the potentiation resulting from the initial high-frequency stimulation. On the other hand, at increasing frequency of stimulation the influence of the initial low-frequency stimulation can depress the tension-time area. The decreasing rate of stimulation during relaxation appeared to support the tension more effectively in slow-twitch motor units than in fast ones. Therefore, slow motor units are well suited to support the tension of tonic contractions.
Celichowski
J
J
Department of Neurobiology, University School of Physical Education, Poznań, Poland. celichowski@awf.poznan.pl
Bichler
E
E
D000818:Animals; D004558:Electric Stimulation / Q000379:methods; D005260:Female; D009119:Muscle Contraction / Q000502:physiology*; D018485:Muscle Fibers, Skeletal / Q000502:physiology*; D018482:Muscle, Skeletal / Q000502:physiology*; D051381:Rats; D017208:Rats, Wistar; D011930:Reaction Time / Q000502:physiology