The influence of mental load on muscle tension

Musculoskeletal disorders (MSDs) have great personal and socio-economic impact and are an important problem to deal with. MSDs mostly result from the cumulative effect of long-lasting load of various magnitudes. Workload and the resulting fatigue – sources of MSDs – have been proved to depend on the type of work task and to stem not only from biomechanical factors, such as exerted force, body posture and time, but also from psychosocial factors.

The authors examined the differences in muscle tension and in physiological measures depending on the type of mental task. They recruited fifteen participants who performed tests for sustained attention, vigilance and maintaining posture only. They analysed electromyogram (EMG) measures of extensor digitorum (ED), flexor carpi ulnaris (FU), deltoideus (DE) and trapezius (TR), and heart rate (HR) and respiratory frequency (RF).

Measures indicated higher values for mental tasks than for maintained posture only with significant differences in all measures. The following relationships were also significant: between DE and physiological measures (HR and RF), between ED and the amplitude of EMG of the other three muscles, between FU and TR and between HR and RF.

Differences in sustained attention, vigilance and maintaining posture only proved that mental demands were mostly reflected by tension in arm and shoulder girdle muscles and, to a lesser degree, in forearm muscles.