Abstract
Poor trunk extensor endurance is implicated in low back pain; less, however, is known about contributions of left and right sides and upper and lower parts to maximum torque production following fatigue. This study examines torque and electromyographic (EMG) activity in different parts of the left and right trunk extensors before and following a maximal voluntary contraction (MVC) hold.
16 student rowers participated and written informed consent was obtained. Testing was performed in a Cybex isokinetic dynamometer with synchronous bilateral EMG recordings (during brief MVCs) from the left and right the erector spinae (ES) muscles at vertebral levels T12 and L4, prior to and immediately after, and 1, 5 and 10 minutes after a 60 second MVC.
A small decrease in maximum torque was observed during 60s MVC, followed by a non significant step-wise increase. The torque at 10 minutes post MVC was the highest value recorded. EMG activity rose in the right upper back 5 and 10 mins following the fatigue. Furthermore, the ratios of left:right EMG activity revealed an increase compared to pre-fatigue values in the lower back but a decrease in the upper back, suggesting the task involved differential use of left and right sides in addition to upper and lower back muscles.
These results suggest that 60s MVC induces differential activation of left and right sides and upper and lower parts of the trunk extensors. The apparent potentiation in force and asymmetry of activation following the 60s MVC task requires further investigation.
Correspondence should be addressed to: Mr John O’ Dowd, SBPR, c/o BOA, The Royal College of Surgeons, 35–43 Lincoln’s Inn Fields, London WC2A 3PE.
