[Frequency spectrum and integral value of electromyographic recordings of the masseter and temporal muscles in correlation with muscle length].

In 15 children and 15 adults the influence of muscle length on the EMG-recordings of the anterior temporal and superficial masseter muscles was investigated. Myoelectric activity was measured by surface electromyography during maximal clenching in habitual occlusion. The quantitative EMG analysis was performed by means of a computer program which allowed calculation of a) the integrated value and b) the mean frequency of the power spectrum (MPF) from the raw signal after Fourier transformation. Muscle length was determined with the aid of lateral cephalometric films. Using a correlation analysis this investigation revealed the following results: Under standardized functional conditions short muscles work with a higher activity and a higher MPF than long muscles. In children as well as in adults muscle activity and MPF show close negative correlations with the parameter "muscle length". These relations are directly proportional.