Interference pattern in perineal muscles: I. A quantitative electromyographic study in normal subjects

The electromyographic pattern (EMG) in two perineal muscles, the external anal sphincter muscle and the puborectalis muscle, was examined in 30 normal subjects consisting of women aged 24–77 years, using a concentric needle electrode. The interference pattern in the two muscles was recorded at rest and at maximal voluntary activation and analyzed with a computerized technique. The number of turns and the mean amplitudes in the interference pattern were measured and the recorded differences between the two investigated muscles as well as the differences compared to other striated extremity muscles are discussed. This technique (T/A analysis) has been shown to differentiate between neurogenic and myopathic changes in a weak muscle, and it is proposed that the technique could be useful in characterizing disturbances in perineal muscles in patients with micturition or defaecation dysfunctions.