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

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

Abstrakty

EN

INTRODUCTION: The changes in force of motor units (MUs) following changes in activation pattern still are not fully understood, especially in relation to effects of decreasing rate of stimuli. It is known that at linearly decreasing stimulation frequency the force decrease is slower than expected when comparing to the constant stimulation frequency. AIM(S): The aim of study was the explanation of recently observed surprising transitory force decrease resulting from a sudden decrease in stimulation frequency. METHOD(S): The research was conducted on 6 adult female Wistar rats under pentobarbital anesthesia. 24 slow (S), 38 fast fatigable (FF) and 65 fast resistant (FR) MUs were isolated. Studied MUs were stimulated with 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. The tested low frequencies for fast MUs were 10, 20, 30, 40 and 50 Hz, and high frequencies amounted to 75, 90 and 150 Hz, whereas for slow motor units low frequencies were 10, 12.5, 15, 17.5, 20 and 25 Hz and high frequencies amounted to 50 and 75 Hz. Moreover, these trains of stimuli were tested at different levels of muscles stretching (30 mN, 100 mN, 200 mN) for all types of MUs. RESULTS: Among the three MU types the studied force decrease was most frequent and the strongest for FR MUs. The highest noted decrease amounted to 36.5%. The greatest transitory force decreases were observed at muscle passive stretch of 100 mN. For MUs of the three types the force decrease was observed at middle-fused tetanic contractions (the fusion index 0.30–0.95). CONCLUSIONS: The phenomenon most probably has biomechanical background and is conditioned by distribution of contracting muscle fibers in a deep part of muscle and slow adaptation of stretched collagen fibers to the lower force level of contracting muscle fibers at reduced stimulation frequency. FINANCIAL SUPPORT: National Science Centre, Poland.

• Wydawca: -
• Czasopismo: Acta Neurobiologiae Experimentalis
• Rocznik: 2017
• Tom: 77
• Numer: Suppl.1
• Opis fizyczny: p.102

Twórcy

autor

Grzesiak J.

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

autor

Krysciak K.

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

autor

Drzymala-Celichowska H.

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

autor

Celichowski J.

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