Adaptations of motoneuron properties after weight-lifting training in rats

Resistance training, with repeated short-term and high-intensity exercises, is responsible for an increase in muscle mass and force. The aim of this study was to determine whether such training induces adaptations in the electrophysiological properties of motoneurons innervating the trained muscles and to relate these adaptive changes to previous observations made on motor unit contractile properties. The study was performed on adult male Wistar rats. Animals from the training group were subjected to a five-week voluntary progressive weight-lifting program, while control rats were restricted to standard cage activity. Intracellular recordings from lumbar spinal motoneurons innervating gastrocnemius and soleus muscles were made under pentobarbital anesthesia. Passive and threshold membrane properties were measured, and rhythmic firing of motoneurons was analyzed. The strength training evoked adaptive changes in both slow and fast-type motoneurons. A shortening of the rise time of action potentials, an increase in input resistance, a decrease in the minimum currents required to evoke rhythmic firing, an increase in the maximum frequencies of rhythmic firing, and an increase in the slope of the frequency-current relationship were observed in motoneurons of the trained group. A range between the minimum and maximum steady state firing frequencies was expanded for fast but not for slow motoneurons. Higher maximum firing rates of motoneurons as well as higher discharge frequencies evoked at the same level of intracellular depolarization current imply higher levels of tetanic forces developed by motor units over the operating range of force production after the strength training.

from Physiology via xlomafota13 on Inoreader http://ift.tt/2s20Th8
via IFTTT