Background. Controlled experiments suggest that active breaks with mental activity interspersed between physical work bouts can lead to more effective recovery from fatigue than passive rest. However, most of these studies investigated a highly stereotyped physical task until exhaustion. Research investigating the effects of mental breaks in tasks of higher occupational relevance is limited. The aim of this study was to evaluate the extent to which a working memory task performed at three difficulty levels would enhance recovery of perceived fatigue after a repetitive physical work task.

Methods. 12 women (mean age 26.4) performed 10 work cycles each comprising seven minutes of pipetting (to model repetitive work) followed by three minutes devoted to a working memory task. Three difficulty levels (MT1, MT2, MT3) of the memory task were tested on three different days in a randomized order across participants. During the last minute of pipetting and after the memory task, participants rated fatigue on the Borg CR-10 scale. Before, during and after each experiment, salivary a-amylase was measured.

Results. Perceived fatigue in the right shoulder during the last minute of pipetting increased with time (p<0.001) but did not significantly differ between types of MT (p=0.314). Perceived fatigue in the right shoulder just after the memory task also increased with time (p<0.001), and in a pattern differing between MT types (time*MT: p=0.042), while MT type showed no significant main effect (p=0.169). Post-hoc tests showed that MT3 led to better recovery than MT1 (effect of MT: p=0.041; time*MT: p=0.025). Salivary a-amylase increased with time (p=0.001) but showed no significant effects of MT type (p=0.214).

Discussion. Our results indicate that recovery of perceived fatigue after a repetitive task was better when performing a difficult — as compared to an easy — memory task. This effect was not accompanied by any differences in a-amylase response.