Activation threshold and contraction dynamics of quadriceps femoris heads measured with ultrasound imaging

Abstract

The assessment of muscle properties is of prime importance in the diagnosis of neuromuscular diseases. Ultrasound imaging is a non-invasive technology which can be used to analyze the dynamics of muscle tissue. Muscle contraction is a brief phenomenon and therefore it is required that the ultrasound apparatus provides short data acquisition times.<br />The present work describes two experiments which have been performed on seven and two healthy voluntary subjects respectively.<br />In the first experiment transcutaneous electrical stimulation of the quadriceps femoris muscle motor points (rectus femoris, vastus lateralis and vastus medialis) and stimulation with large surface electrodes were applied and the threshold voltages for muscle activation were determined using M-mode ultrasound imaging. Simultaneously electromyography and acceleromyography signals were recorded and the results were compared to those of ultrasound imaging in terms of selectivity and sensitivity.<br />Furthermore, the contraction induced by the stimulation with large surface electrodes was analyzed using ultrasound B-mode imaging.<br />In the second experiment the contraction dynamics of the quadriceps femoris heads were studied using superthreshold stimulation voltages.<br />The motor points were stimulated selectively, but also the femoral nerve was stimulated transcutaneous to activate the vastus intermedius muscle.<br />Changes in muscle diameter were determined and compared to the peak-to-peak amplitudes and RMS values of simultaneous recorded electromyography and acceleromyography signals. Muscle twitch rise times were measured and compared to muscle fiber composition values found in the literature.<br />The thesis provides an insight on the behavior of muscle and potential muscle contractions.