Katarzyna Kryściak1, Jan Celichowski1, Hanna Drzymała-Celichowska1, Phillip F Gardiner2, Piotr Krutki1. 1. Department of Neurobiology, University School of Physical Education in Poznan, 27/39 Królowej Jadwigi Street, 61-871, Poznań, Poland. 2. Spinal Cord Research Center, and Faculty of Kinesiology & Recreation Management, University of Manitoba, Winnipeg, Manitoba, Canada.
Abstract
INTRODUCTION: The influence of long-term muscle overload on force regulation and electrical properties of motor units (MUs) was investigated in rats. METHODS: Compensatory overload of the medial gastrocnemius was induced by tenotomy of its synergists. Electrophysiological experiments were performed on functionally isolated MUs 3 months after the surgery. RESULTS: Force-frequency curves for overloaded MUs were shifted rightward compared with control, thus MUs developed the same relative tetanic forces at higher frequencies. Higher force increase was achieved in response to an increase in stimulation frequency in overloaded fast MUs compared with control. The optimal tetanic contraction, characterized by the highest force-time area per pulse, was evoked at higher stimulation frequencies for all overloaded MUs except FF. Only minor adaptive changes in MU action potentials occurred. CONCLUSIONS: Compensatory muscle overload leads to substantial modifications in MU force development mechanisms, which are MU-type-specific and influence whole muscle force regulation.
INTRODUCTION: The influence of long-term muscle overload on force regulation and electrical properties of motor units (MUs) was investigated in rats. METHODS: Compensatory overload of the medial gastrocnemius was induced by tenotomy of its synergists. Electrophysiological experiments were performed on functionally isolated MUs 3 months after the surgery. RESULTS: Force-frequency curves for overloaded MUs were shifted rightward compared with control, thus MUs developed the same relative tetanic forces at higher frequencies. Higher force increase was achieved in response to an increase in stimulation frequency in overloaded fast MUs compared with control. The optimal tetanic contraction, characterized by the highest force-time area per pulse, was evoked at higher stimulation frequencies for all overloaded MUs except FF. Only minor adaptive changes in MU action potentials occurred. CONCLUSIONS: Compensatory muscle overload leads to substantial modifications in MU force development mechanisms, which are MU-type-specific and influence whole muscle force regulation.
Authors: Katarzyna Kryściak; Joanna Majerczak; Jakub Kryściak; Dawid Łochyński; Dominik Kaczmarek; Hanna Drzymała-Celichowska; Piotr Krutki; Anna Gawedzka; Magdalena Guzik; Michał Korostynski; Zbigniew Szkutnik; Elżbieta Pyza; Wiesława Jarmuszkiewicz; Jerzy A Zoladz; Jan Celichowski Journal: PLoS One Date: 2018-04-19 Impact factor: 3.240