Muscle- and task-dependent responses to concurrent physical and mental workload during intermittent static work

Area of Science:

• Occupational Health
• Ergonomics
• Human Factors Engineering

Background:

• Many jobs involve simultaneous physical and mental demands, but their impact on musculoskeletal disorders is not fully understood.
• Understanding these combined demands is key to preventing workplace injuries and improving worker well-being.

Purpose of the Study:

• To examine how concurrent physical and mental demands affect muscle activity, cardiovascular load, and motor coordination during static work.
• To identify muscle- and task-specific responses to combined occupational stressors.

Main Methods:

• Twenty-four participants performed intermittent static exertions (shoulder, wrist, torso) at varying physical workload levels.
• Exertions were conducted under control (physical only) and concurrent (physical + mental arithmetic task) conditions.
• Muscle activity, cardiovascular load, and motor coordination (force fluctuation) were measured.

Main Results:

• Concurrent demands led to reduced muscle activity (4-9%) and increased cardiovascular load (2-4%) compared to physical demands alone.
• Motor coordination was impaired, with force fluctuations increasing by 9-24% under concurrent demands.
• These effects were more pronounced at higher physical workload levels and in postural muscles (shoulder, torso).
• Mental task performance was significantly affected by physical workload, showing greater interference at low and high levels.

Conclusions:

• Combined physical and mental job demands significantly alter physiological responses and motor control.
• Muscle and task-specific interactions are critical when considering the effects of concurrent demands.
• Job design should account for these complex interactions to mitigate risks of musculoskeletal disorders and enhance worker performance.