The transitory force decrease following high-frequency stimulation burst in unfused tetani of motor unit

• Autorzy: Grzesiak J. , Drzymala-Celichowska H. , Celichowski J.
• Języki publikacji: EN

Abstrakty

EN

BACKGROUND AND AIMS: The changes in force of motor units (MUs) following changes in activation pattern are still not well understood, especially in relation to the relaxation course at decreasing rate of stimuli. It is known that at linearly decreasing stimulation rate the force decrease is slower than expected when comparing to the constant stimulation frequency. The present study aimed to verify a hypothesis that at a sudden decrease of stimulation frequency the force decrease is also lower than expected. METHODS: The research was conducted on 4 adult female Wistar rats under pentobarbital anesthesia. 8 slow (S), 16 fast fatigable (FF) and 26 fast resistant (FR) MUs were isolated. Studied MUs were stimulated with the several trains of stimuli composed of three phases: first, 500 ms at low frequency, second, 300 ms at high frequency and third, 500 ms at the same low frequency for fast motor units and 1000 ms at low frequency, second, 300 ms at high frequency and third, 1000 ms at the same low frequency for slow motor units. The tested low frequencies for fast MUs were 10, 20, 30, 40 and 50 Hz, and high frequency amounted to 75 Hz, whereas for slow motor units low frequencies were 10, 12.5, 15, 20 and 25 Hz and high frequency amounted to 50 Hz. RESULTS: Surprisingly, for MU of the three types at the middlefused tetanic contractions (the fusion index 0.15–0.80) the sudden switch from high to low frequency evoked the transitory force decrease below the force level at initial low-frequency stimulation. On the average the decrease amounted to 15.99% and the highest noted decrease amounted to 40%. Among the three MU types the force decrease was most frequent and the strongest for FR MUs. CONCLUSIONS: The phenomenon most probably is related to low-force generating state of cross-bridges in muscle fibers at a new overlapping following the force decrease and/or to a slow adaptation of stretched collagen fibers to the lower force level in the contracting muscle.

• Wydawca: -
• Czasopismo: Acta Neurobiologiae Experimentalis
• Rocznik: 2015
• Tom: 75
• Numer: Supl.
• Opis fizyczny: p.S74

Twórcy

autor

Grzesiak J.

• Department of Neurobiology, University School of Physical Education, Poznan, Poland

autor

Drzymala-Celichowska H.

• Department of Neurobiology, University School of Physical Education, Poznan, Poland

autor

Celichowski J.

• Department of Neurobiology, University School of Physical Education, Poznan, Poland