Effects of cognitive loading and force on upper trapezius fatigue

Background: Musculoskeletal disorders (MSDs) are particularly common in the shoulder/neck region for some tasks that involve low force exertions, for example computer work. It has been demonstrated that muscle activity may be stimulated by cognitively demanding tasks. There is a lack of studies on the relationship between qualitative levels of cognitive loading, level of muscle activity, and muscle fatigue. Aims: To investigate the effects of quantitative levels of cognitive loading on conduction velocity changes and isometric endurance times for the upper trapezius. Methods: Participants performed a combination of three levels of a cognitively demanding computer task (0, 1.59 and 3 Bits) while simultaneously performing either of two isometric endurance tests (20 and 40% MVC) for the upper trapezius. Results: Information load had a significant effect (P < 0.05) on normalized conduction velocity slopes for the 40% but not for the 20% maximum voluntary contraction conditions. Information load had a highly significant effect on endurance times for both exertion levels (P < 0.01). Conclusions: This study found that performing a high-difficulty cognitive task while simultaneously performing increasingly higher levels of static isometric shoulder abduction exertions, fatigued the trapezius muscle quicker than performing an equivalent exertion with low cognitive load. This is particularly relevant to workplaces with increasing levels of automation that require high levels of decision making and computer use.