Power spectra characteristics associated with static reflexive activation of the multifidus muscle in feline models

The aim of the study was to track changes in the spectrum of electromyographic (EMG) signals recorded from the feline multifidus muscles during stretching of the supraspinous ligament. The ligaments were exposed to external 40 N-tension for six consecutive trials of 10-min duration. Two experimental groups were formed, according to the rest periods supplied (10 or 20 min). EMG signals were recorded intramuscularly from the right multifidus muscles. The EMG signals from each trial were split into segments. For each segment, a representative averaged motor unit potential (AvMUP) was determined. The number of single MUPs averaged to obtain AvMUP was defined as muscular activity. The relative changes in a muscle fatigue index, median frequency as well as activity were analyzed. It was concluded that faster and powerful motor units are recruited firstly, in order to quickly provide stronger support to the spine and/or as a reaction to a minor damage of tissue. Depending on the applied rest periods, peripheral fatigue might be accumulated.