One explanation for the higher relative EMG level for the elderly may be more co-activation of antagonist muscles, which has been found in another laboratory study (Spiegel et al 1996). The muscles responded significantly different to the different mouse tasks, although the differences were minor. The task causing the highest muscle activity was double clicking for the wrist flexors and extensors, and the self-selected speed clicking tasks for the finger extensors. Increased precision demands cause an increased muscle activity when the working speed was fixed in agreement with what has been found previously ( Laursen et al.; 1998). When the speed was self-selected, the precision demand had no effect on muscle activity.
In conclusion, the elderly performed the mouse work slower than the young group but with the same error rate, when the working speed was self-selected. Double clicking caused many errors for the elderly group. The relative muscle load was higher for the elderly group. There were small but significant differences in muscle load between the different mouse tasks.
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