The relationship between estimates of puborectalis muscle shear modulus made with shear wave elastography and electromyography in healthy men

This study aimed to: (i) describe a method to estimate shear modulus of the male puborectalis muscle using shear wave elastography (SWE); (ii) investigate the relationship between changes in shear modulus and electromyography (EMG) of the left and right puborectalis muscle; (iii) investigate whether measures made at rest differ before and after a maximal voluntary contraction; and (iv) investigate whether rest measures are consistent over repeated submaximal contractions. Eleven males with no history of pelvic symptoms participated. Puborectalis muscle SWE was recorded using a transperineal ultrasound. Puborectalis EMG was recorded with a custom electrode stabilized to the anal mucosa with suction. Measures were made during rest and contractions at 10, 20, 30, 50 and 75% of maximal voluntary contraction (EMG). Correlation between normalized EMG and shear modulus data over contraction intensities was calculated (left; right). Amplitude of each measure at rest was compared before and after maximum voluntary contraction and before each submaximal contraction. Group data showed strong linear correlations between shear modulus and EMG for the left r2=0.71 [SD 0.16; 95% CI 0.61−0.81], and right r2=0.56 [0.33; 0.35−0.76] puborectalis and there was no difference in the correlation between sides (p = 0.17), or between rest values of EMG or shear modulus before and after maximal and submaximal contractions (all p>0.31). This study confirms the viability of SWE for measurement of the puborectalis muscle in men and validity of changes in SWE as an estimate of shear modulus/stiffness of this muscle. Healthy men returned to rest values after contraction at different intensities.