Tolerability to prolonged lifting tasks. A validation of the recommended limits

Area of Science:

• Ergonomics and Occupational Health
• Human Physiology
• Biomechanics

Background:

• Prolonged physical exertion is managed by subjective effort perception.
• Assessing tolerable workloads for manual handling is crucial for preventing injuries.
• Previous research lacks objective validation of subjective effort in prolonged lifting.

Purpose of the Study:

• To validate subjective perceptions of effort for determining objectively tolerable workloads in prolonged lifting.
• To establish an "iso-perception" curve for individual tolerance thresholds.
• To propose a quantifiable lifting threshold based on perceived exertion.

Main Methods:

• Ten healthy males performed maximal, incremental, and endurance lifting tests using a lift dynamometer.
• Cardiorespiratory parameters and mechanical work were monitored and calculated.
• Subjective ratings of perceived exertion (Borg scale) were correlated with physiological and mechanical data using statistical regression.

Main Results:

• "Iso-perception" curves were generated, linking perceived effort to mechanical work.
• A "moderate" perception of effort correlated with stable physiological responses and a respiratory exchange ratio < 1.
• A lifting tolerance threshold of 20% of maximal lifting capacity (MLC) was proposed for 30-minute tasks.

Conclusions:

• Subjective "moderate" effort perception serves as a reliable indicator of the tolerance threshold for prolonged lifting.
• The proposed 20% MLC threshold offers a guideline for safe manual handling, aligning with ergonomic principles.
• This preliminary study supports integrating subjective feedback into objective workload assessment for occupational safety.