The Relationship Between Length, Velocity, EMG and Force in the isolated Human Biceps Brachii Muscle

Abstract

<p> The force-velocity and force-length relationships of skeletal muscle have been thoroughly investigated in the literature. Unfortunately many of the relationships that have been applied to models of the human anatomy have been based upon investigations that have been performed under in-vitro conditions. It was the intention of this study to investigate whether the relationships determined by in-vitro investigation and assumed to be correct could accurately and properly be applied to actual human examples. Previous investigation by Leedham and Dowling (1991) displayed that when investigating human elbow flexors and in particular the biceps brachii that the force-length relationship did not concur with in-vitro results. The purpose of this study was to investigate the relationships between length, velocity, EMG and force of the biceps muscle. </p> <p> Eight young adult males (22-26) were fastened into an isoveloci ty device ( CYBEX) which allowed only flexion and extension of the right elbow. The forearm was then rotated eccentrically or concentrically through a range of motion from 50 to 170 degrees of extension (or vice-versa). The biceps muscle was either maximally contracted voluntarily or was excited using electrical stimulation at 40 Hz. Using the constant angle torque (CAT) method and three dimensional surfaces the force-velocity, force-length and EMG-velocity relationships were investigated. <p> <p> The main conclusions of the study were that the neural drive provided by electrical stimulation over the motor point provided CMAPS of consistent amplitude regardless of the joint angle or angular velocity. The concentric force-velocity relationship of the biceps was in agreement with most accounts in the literature however the eccentric contraction condition displayed a peak force production at 30° Is then showed a slight decline to plateau across faster eccentric velocities. Increased eccentric force production was thought to be more mechanical than neurological in nature. </p>