Muscle temperature alters the EMG power spectrum of the canine diaphragm

Electromyogram (EMG) power spectral analysis has been widely used to detect muscle fatigue. Non-fatigue factors that influence the EMG power spectrum must be well understood to ensure accurate interpretation. We explored the effect of muscle temperature on the EMG power spectrum in an isolated canine diaphragm preparation with intact neuro-vascular supply. In 5 animals, diaphragm temperature was continuously recorded with an intramuscular thermocouple, and the EMG signal was recorded with intramuscular wire electrodes. Data were obtained from spontaneous isometric diaphragm contractions while the diaphragm underwent passive cooling from 40 to 30 degrees C. The EMG power spectrum was determined using fast Fourier transform and each spectrum was characterized by its center frequency (fc). A direct linear relationship was found between diaphragm temperature and the EMG fc. The mean slope of the temperature-EMG fc relationship was 2.9% fc.degree C-1. In conclusion, diaphragm temperature is a major determinant of the diaphragmatic EMG power spectrum, and should be controlled when this index is employed in the investigation of muscle fatigue.