Quantification of motor unit activity and steadiness in a functional task

• Main Author: Cornett, Kayla Margaret Dawn
• Language: English
• Published: University of British Columbia 2013
• Online Access: http://hdl.handle.net/2429/45478

The ability to control functional movement is essential for daily life. Extensive literature exists on lower motor unit (MU) recruitment thresholds and greater discharge rates in anisometric compared with isometric contractions. This difference is in-part related to task specificity. To-date the spinal control of functional movement has not been evaluated relative to the performance of functional movement. The purpose of this thesis was to quantify and evaluate MU activity and steadiness in a functional task compared to anisometric and isometric contractions. Thirteen female subjects (22.5 ± 2.9 years) were recruited. Surface and intramuscular electromyography (EMG) were recorded from the elbow flexor muscles. Subjects performed 4 experimental contractions; 1. a waterbottle drinking task where subjects lifted a waterbottle, took a sip of water and lowered the bottle (functional task); 2. a waterbottle lifting task performed identical to the previous but without drinking; 3. an anisometric contraction matched for load, range of motion, and acceleration; 4. a load matched isometric contraction. Repeated measures ANOVAs were used to assess EMG, MU recruitment and discharge rates and steadiness between the contractions. Surface EMG was not different between the three movement tasks but lower during the isometric contraction. The waterbottle drinking task had the highest discharge rate, as well as discharge rate variability and was the least steady. There were no differences in recruitment between the 4 contraction types. This was the first study to evaluate MU activity in functional tasks. It is clear that functional tasks require unique activation strategies which occur primarily through alterations in MU discharge rate. Thus, spinal control is not only task specific, but also related to goal-directed outcomes of the movement.