Saccadic reaction times during isometric contraction of each side of unilateral shoulder girdle elevator

Abstract

  We compared the saccadic reaction times during isometric contraction of bilateral shoulder girdle elevators and unilateral (right and left) shoulder girdle elevator in a sitting posture. Muscle contraction force was increased in 10% increments from 10% to 60% of the maximal voluntary contraction (MVC) of each side. Saccadic reaction time was determined as the latency to the beginning of eye movement toward a lateral target moved at random intervals in 20° amplitude jumps. Eye movement was measured using the electrooculographic technique. During bilateral contraction, the saccadic reaction time decreased until 30% MVC and then began to increase at 40% MVC. In both right and left contractions, saccadic reaction time decreased until 30% MVC similar to bilateral contraction, but remained constant from 30% to 50% MVC that differed from bilateral contraction, followed by a slight increase at 60% MVC. The saccadic reaction times at 50% and 60% MVC were significantly shorter during unilateral contraction compared to bilateral contraction. These results demonstrated that the saccadic reaction time produced by shoulder girdle elevator contraction is shortened at a wider range of muscular force during unilateral contraction than bilateral contraction, and that the saccadic reaction time did not differ significantly between right and left contraction.