FATIGUE AND EMG CHANGES IN THE MASSETER AND TEMPORALIS MUSCLES DURINGSUSTAINED CONTRACTIONS

Local muscle fatigue was investigated in the anterior temporal and mas seter muscles during sustained isometric contractions. The volunteers' subjective perception of fatigue or pain was recorded at intervals du ring the sustained contractions, and this level was then compared to o bjective measures of fatigue. These objective measures included shift in median frequency of the power spectrum of the surface-detected EMG signal, and change in signal amplitude. The relationship was investiga ted while closing on a bite force meter placed between the second prem olars and first molars unilaterally, and while simply clenching with t he teeth together without the bite force meter. It was found that the subjective perception of fatigue, as measured on a visual analogue sca le (VAS), had a nearly linear relationship with time, and that the rel ationship between the VAS score and median frequency shift was rather closer than the relationship with amplitude change.