The relationship between RMS electromyography and thickness change in the skeletal muscles

The knowledge of muscle function may affect prescribing medications and physical treatments. Recently, ultrasound and electromyography (EMG) have been used to assess the skeletal muscles activity. The relationship between these methods has been reported in numerous articles qualitatively. In this paper, the relationship between EMG root-mean-square (RMS) and ultrasound data of muscle thickness has been investigated using Response Surface Methodology in the muscles separately and together and predictive models reported. Results show that to assess the relationship between the changes of thickness and activity (EMG) in muscles, we can use quadratic model for the rectus femoris, tibialis anterior, transverse abdominal, biceps brachii and brachialis muscles (R²=0.624-0.891) and linear model for the internal and external oblique abdominal, lumbar multifidus and deep cervical flexor muscles (R²=0.348-0.767). Due to the high correlation coefficient for the equations in the bulky muscles, it seems that the correlation between EMG RMS and ultrasound data of muscle thickness on the bulky muscles is higher than the flat muscles. This relationship may depend more on the type of activity than the type of muscle.