Background: Although combinations of physical and cognitive work tasks occurs in working life (both concurrent and alternating), no one has summarized the research regarding such combinations. Very few studies have investigated the effects of alternating physical and cognitive tasks, which have been suggested as an alternative to classic job rotation. The aim with this thesis was to investigate the effects of concurrent and alternating cognitive and physical work tasks on fatigue, stress, recovery, and performance and whether the task difficulty and the temporal pattern is important in this respect. 

Methods: In study I, 48 controlled studies comprising combinations of physical and cognitive work tasks was summarized in a systematic review. In two controlled experiments (study II, III and IV), participants performed alternations of a physical and a cognitive task. In study II and III, the difficulty levels of the cognitive task was varied between conditions, and in study IV, the temporal patterns and cognitive task difficulty was varied between conditions. During work, indicators of fatigue (study II and IV), stress (study III and IV) and performance (study II and IV) was assessed. 

Results: Concurrent physical and cognitive work tasks have a negative impact on biomechanical indicators, fatigue and performance, while the effect on stress seems mixed. Alternating physical and cognitive work tasks leads to some accumulated fatigue over time, with physical recovery taking place during the cognitive task. Indicators of stress did not increase over time, and neither fatigue nor stress was influenced by cognitive task difficulty. 

Conclusions: Concurrent physical and cognitive work should be avoided in working life and if they must be performed, employers should decrease task demands. Alternations on the other hand, could be carried out without excessive fatigue or stress, and with maintained performance. This thesis provides a basis for recommendations on how to properly organize job-rotation schemes. 

Bakgrund: Kombinationer av fysiska och kognitiva arbetsuppgifter förekommer i många yrken (både samtidiga och alternerande), men ännu har ingen sammanfattat forskningen gällande effekterna av sådana kombinationer. Väldigt få studier har undersökt effekterna av alternerande fysiska och kognitiva uppgifter, vilket har föreslagits som ett alternativ till klassisk jobbrotation. Syftet med denna avhandling var att undersöka effekten av samtidiga och alternerande fysiska och kognitiva arbetsuppgifter på trötthet, stress, återhämtning och prestation, och i vilken utsträckning som den kognitiva arbetsuppgiftens svårighetsgrad och tidsmönstret av alterneringarna har betydelse för utfallen.

Metod: I studie I sammanfattades 48 studier bestående av kombinationer av fysiska och kognitiva uppgifter i en systematisk litteraturöversikt. I två kontrollerade experiment (Studie II, III och IV), utförde deltagare alterneringar av en fysisk och en kognitiv uppgift. I studie II och III varierades svårighetsgraden av den kognitiva uppgiften mellan betingelserna, och i studie IV varierades både svårighetsgraden och tidsmönstret av alterneringar mellan betingelserna. Under arbetet mättes indikatorer på trötthet (studie II och IV), stress (studie IIIoch IV) och prestation (studie II och IV).

Resultat: Samtidiga fysiska och kognitiva arbetsuppgifter har en negativ inverkan på biomekaniska indikatorer, trötthet och prestation, medan effekten på stress är mer oklar. Alternerande fysiskt och kognitivt arbete leder till viss ackumulerad trötthet över tid, men med fysisk återhämtning under den kognitiva uppgiften. Indikatorer på stress ökade inte över tid, och varken trötthet eller stress påverkades av den kognitiva uppgiftens svårighetsgrad.

Slutsatser: Samtidiga fysiska kognitiva uppgifter bör undvikas i arbetslivet och om de måste utföras, bör arbetsgivaren minska arbetsuppgiftens krav. Alterneringar verkar å andra sidan kunna utföras utan större påverkan på trötthet och stress, och med bibehållen prestation. Resultaten från den här avhandlingen kan utgöra en bas för rekommendationer om hur arbetsrotationer ska organiseras.

The aims of this questionnaire study were to describe the occurrence and desired number of alternations between mental and physical tasks in industrial and non-industrial blue-collar work, and determine to which extent selected personal and occupational factors influence these conditions. On average, the 122 participating workers (55 females) reported to have close to four alternations per day between mental and physical tasks, and to desire more alternations than they actually had. They also expressed a general preference for performing a physical task after a mental task and vice versa. In univariate regression models, the desired change in task alternations was significantly associated with Gender, Age, Occupation, Years with current work tasks, and Perceived job control, while Occupation was the only significant determinant in a multiple regression model including all factors. Our results suggest that alternations between productive physical and mental tasks could be a viable option in future job rotation.

Background. Health and well-being at work is generally assumed to be associated with sufficient physical and mental variation. Job rotation, where workers typically alternate between different physical tasks, is a popular initiative. Controlled experiments suggest that favourable effects are associated with alternations between mental and physical tasks, but little is known about this intervention in real work. The aims of this study were (1) to describe the occurrence of alternations between mental and physical tasks, and (2) to identify key determinants of such alternations.

Method. We developed a questionnaire combining established questions with specific questions about alternations. Workers from two occupations (industrial and non-industrial blue-collar work), in jobs containing both physical and mental tasks, were included in the study. 122 (55 females) out of 293 workers approached at four companies answered the questionnaire.

Results. On average, the workers alternated 3.5 times per day between mental and physical tasks. In the non-industrial companies, workers reported wanting more alternations than they had, while desired and actual alternations did not differ in the industrial companies. This effect of occupation on the difference between the number of alternations wanted and the actual alternations available was significant (p < 0.001). Furthermore, there was a general preference for performing a physical task after a mental task, and vice versa. This main effect of primarily performed task type (i.e. either physical or mental) on preferred subsequent task type was significant (p < 0.001). In a univariate analysis, gender appeared to be a strong determinant of the occurrence of alternations, but the effect was absorbed when adding the occupation variable.

Discussion. Within the studied companies, work offered alternations between mental and physical tasks and there was a preference among workers to alternate between tasks. Occupation rather than gender was a key determinant of the number of alternations reported.

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.