Effects of artifacts in a repetitive light assembly task on muscular activity according to age and work rate constraints

Time constraints can be particularly stressful for older workers in repetitive work. Opportunities for work rate regulation could offer a way of dealing with production variations. The aim of this laboratory study was to investigate the effects of occurrence of artifacts on muscular activity under two work rate conditions for a repetitive task completed by younger and older participants (YPs and OPs).
14 YPs (25-35 years) and 14 OPs (55-65 years) performed an assembly task (with a theoretical cycle time (TCT) of 22s) under 2 conditions: C1, a forced work rate with a production penalty (PP) if the task was not completed within the TCT; and C2, a more flexible work rate with a PP inflicted if 3 consecutive cycle times were greater than 3 TCT (66s). For each condition, participants made 136 assemblies with 15 % of them being artifacts assemblies (AA) which required supplementary operations within the same TCT. Assembly time (ATime) and EMGs of the right Flexor Digitorum Superficialis (FDS-R), Extensor Digitorum Communis (EDC-R), Biceps Brachii (BB-R), Triceps Brachii (TB-R) and right and left Deltoid (DEL-R/L) and Trapezius (TRA-R/L) muscles were recorded.
ATime was greater for AAs than for non AAs for all participants under C1 only (p < 0.001). Under C1, EMGs of all muscles, except TRA-R/L, were greater for AAs than for non AAs for all participants (p < 0.001). In C2, EMGs of FDS-R, EDC-R, BB-R, TB-R and DEL-R were greater for AAs than for non AAs for OPs only (p < 0.001). The number of PPs was greater under C1 than under C2 (p < 0.001).
Giving leeway in time made it possible to improve performance and to reduce muscular activity. However older workers needed to pay special attention when coping with artifacts since their muscular strains remained higher than for standard assemblies