Psychophysical lifting capacity over extended periods.

Area of Science:

• Occupational Health
• Ergonomics
• Human Factors Engineering

Background:

• Assessing lifting capacity is crucial for preventing workplace injuries.
• The psychophysical approach uses subjective perception to determine safe lifting limits.
• Long-term effects of lifting frequency on perceived exertion are not fully understood.

Purpose of the Study:

• To investigate the effect of time on lifting capacity using a psychophysical approach.
• To compare maximum acceptable weight of lift (MAWOL) over extended periods with varying conditions.
• To evaluate the validity of the psychophysical method at different lifting frequencies.

Main Methods:

• Twelve male subjects performed an 8-hour lifting task after an initial 25-minute capacity estimation.
• Subjects either adjusted the weight to maintain perceived exertion or lifted a pre-set weight.
• Lifting capacity was assessed using the psychophysical method, measuring maximum acceptable weight of lift (MAWOL).

Main Results:

• When weight was adjustable, the final MAWOL averaged 85.4% of the initial estimate.
• At a low lifting frequency (2 lifts/min), all subjects completed the 8-hour task.
• At a high lifting frequency (8 lifts/min), only 3 out of 12 subjects completed the task.

Conclusions:

• The psychophysical approach is valid for lower lifting frequencies but overestimates capacity at higher frequencies.
• Sustained lifting over 8 hours leads to reduced lifting capacity, especially at higher frequencies.
• Physiological measures like heart rate and oxygen consumption showed slight fluctuations during the task.