| Abstract: | This study investigated the relationship between the reaction time of eye movement (RTEM) and activity of the superficial
neck extensor muscles when the shoulder girdle elevator muscles contracted isometrically. The results were compared with those
of a previous study in which the subjects's head was fixed and loaded with the neck flexed. When the shoulder girdle elevator
muscles contracted isometrically, RTEM decreased significantly in comparison to RTEM at rest. This demonstrated that the reaction
time significantly decreased not only as a result of the neck in flexion, which activated the deep and superficial neck extensor
muscles, but also from contraction of the shoulder girdle elevator muscles which mainly activated the superficial extensor
muscles. The relationship between RTEM and relative muscle load of the shoulder girdle elevator muscles showed that RTEM decreased
up to 30% loading, and with loading above 40% the RTEM was longer than with 30%. The relative muscle load for the shortest
RTEM demonstrated a subject-to-subject variance ranging from 24.7% to 49.6%. The difference between RTEM at rest and at their
shortest reaction time was approximately 20 ms, which was consistent with the data for the neck in flexion. However, the relative
muscle load for the shortest RTEM differed between the current and previous studies. The parameters obtained in this study
were higher than for those in the previous study. |
