Motor units of medial gastrocnemius muscle in the rat during the fatigue test. II. Changes in the time course of sequential tetani of fatigue test.
Seventy motor units (MUs) of 3 types: fast fatigable (FF), fast resistant to fatigue (FR) and slow (S) were studied in medial gastrocnemius muscle of the rat. The fatigue test time course showed significant variability. It was found, that slow MUs, apart from greater resistance to fatigue, had less variable tetanic time course during the fatigue test than the fast MUs. The tetani of fast MUs were unfused with a marked sag. At the beginning of fatigue test the tension of fast motor units increased. The increase appeared to be greater and more rapidly developing in FF than in FR MUs. In the next part of fatigue test, when decrease in the tetanic tension was observed, the tetanic time course was changing in FF but not in FR MUs. During the first tetanus of fast MUs the sag exhibited a significant variability of its time course. In a proportion of fast MUs the sag appeared again when their tension was potentiated but in such a case it showed a different time course. The obtained results point to high degree of specialization of MUs in the studied muscle.
Celichowski
J
J
Department of Neurobiology, Academy of Physical Education, Poznań, Poland.
D000818:Animals; D004558:Electric Stimulation; D066298:In Vitro Techniques; D009046:Motor Neurons / Q000502:physiology*; D009119:Muscle Contraction / Q000502:physiology; D009132:Muscles / Q000502:physiology*; D051381:Rats