Functional differentiation within latissimus dorsi.

"Functional differentiation" within skeletal muscle refers to the ability of the Central Nervous System (CNS) to control, with a degree of independence, individual subunits of a muscle during a particular muscle contraction. Essentially, the concept of functional differentiation within skeletal muscle suggests an ability of the CNS to selectively activate those segments of a muscle which have the most appropriate line of action for the task as a means of ensuring the muscles efficient utilisation. The present study was undertaken to determine whether functional differentiation was present within the radiate muscle, Latissimus Dorsi, during a series of isometric muscle contractions. Six surface electrode pairs were placed along the origin of the muscle and electromyographic (EMG) potentials were recorded during isometric contractions in various planes and levels of contraction intensity. The EMG waveforms were integrated (IEMG) and then normalised. The normalised EMG waveforms (nIEMG) were then statistically compared to determine if muscle fibres within the detection area of each electrode pair had varied their contribution to the total activity of the muscle, from one isometric contraction to another. Alterations in the contribution of each site were taken to be indicative of functional differentiation. The results of this study indicated that functional differentiation did occur within Latissimus Dorsi. In essence, the most caudal fibres were utilised preferentially when subjects performed adduction from an abducted position of the shoulder joint. Conversely, activity was distributed over the entire muscle when subjects attempted adduction from the anatomical position. A similar situation was observed when subjects performed horizontal extension from either a flexed or abducted position.(ABSTRACT TRUNCATED AT 250 WORDS)