Effect of load level on the emg spectra of longissimus thoracis muscle during isometric fatiguing contractions.

The present study analyzed the effect of different magnitudes of isometric contraction of longissimus thoracis muscle until fatigue by means power spectra analysis. Eight healthy male subjects volunteered for this study The electromyography signals were sampled at 1 kHz using surface electrodes placed bilaterally over the longissimus thoracis muscle at the level L1. The isometric contraction was made at 30% and 60% of isometric maximal voluntary contraction (MVC) randomly in the MA ISOSTATION 2001 with the trunk at 45 degrees of flexion. A gain of 1000, a high pass filter at 20 Hz and low pass filter at 500 Hz was used. The endurance time with the load of 30% was longer than the load of 60%. It was found a significant drop in the median frequency and in the mean power frequency for both loads in both sides with progression of time. Also, analyzing the load effect, it was found significant differences in the total power and peak power for the longissimus thoracis in the interval of 0-100%, with lower values to 30%. The present study allows verifying the longissimus thoracis muscular fatigue by means the electromiographics parameters. It was showed that the total power and the peak power variables are sensible due changes in the load, once there are low values for the low loads.