The course of motor unit twitch in dependence on muscle stretching force. Studies on medial gastrocnemius muscle of the rat.
Studies were performed on 46 units of medial gastrocnemius muscles in 23 rats. In the examined population, three types of motor units were distinguished: fast fatigable (FF), fast resistant (FR) and slow (S) units. The studied muscle was stretched with force gradually increasing from 0.5 to 10 g. Most of FF units and some of FR units reached the highest twitch force when the muscle was stretched with 4 to 7.5 g. The remaining fast units and almost all slow units reached the highest twitch force at 10 g stretching of the muscle. In some fast units, twitch force even decreased slightly at stretching of the muscle with 10 g force. On the other hand, contraction time and half-relaxation time were getting prolonged in the whole process of stretching the muscle. Most pronounced changes in contraction time and half-relaxation time took place in S type units while the least pronounced ones - in FF type units. The prolongation of half-relaxation times in motor units of all three types was more pronounced than the prolongation of contraction times.
Grottel
K
K
Department of Neurobiology, Academy of Physical Education, Poznań, Poland.
Celichowski
J
J
Anissimova
N
N
D000818:Animals; D006614:Hindlimb; D009046:Motor Neurons / Q000502:physiology*; D009119:Muscle Contraction / Q000502:physiology; D009126:Muscle Relaxation / Q000502:physiology; D009132:Muscles / Q000502:physiology*; D051381:Rats; D011919:Rats, Inbred Strains