Job enlargement and mechanical exposure variability in cyclic assembly work

Area of Science:

• Occupational Health
• Ergonomics
• Biomechanics

Background:

• Cyclic assembly work is associated with a high risk of musculoskeletal disorders.
• Job rotation (task variation) is hypothesized to mitigate this risk by increasing mechanical and psychological exposure variability.

Purpose of the Study:

• To investigate the impact of job enlargement on mechanical exposure variability in electronics assembly tasks.
• To assess the cycle-to-cycle variance in muscle activity and posture across different workstations and a combined job enlargement scenario.

Main Methods:

• Electromyography (EMG) measured upper trapezius and forearm extensor muscle activity.
• Inclinometry assessed head and upper arm postures.
• Analysis of variance (ANOVA) calculated cycle-to-cycle variance for EMG and posture parameters across three workstations and a job enlargement scenario.

Main Results:

• Job enlargement increased between-cycle variance in muscle activity and posture, up to sixfold compared to single-station work.
• Trapezius muscle activity showed higher variability than forearm extensors, with job enlargement effects being more pronounced.
• Variability changes varied by muscle group and posture; some stations showed reduced forearm extensor variability with job enlargement.

Conclusions:

• Job enlargement significantly increases exposure variability in cyclic assembly work, particularly for the upper trapezius muscle.
• The effectiveness of job enlargement in reducing musculoskeletal disorder risk requires further investigation into the sufficiency of observed variability changes.