Predicting Endurance Time in a Repetitive Lift and Carry Task Using Linear Mixed Models

Area of Science:

• Occupational Health
• Ergonomics
• Human Physiology

Background:

• Repetitive manual handling tasks contribute significantly to workplace injuries.
• Limited data exists on endurance time for these tasks, hindering the development of safe work guidelines.

Purpose of the Study:

• To investigate the relationship between carry mass and endurance time in a repetitive lift and carry task.
• To assess oxygen consumption during repetitive lifting and carrying.
• To provide data for informing work-rest schedules and physical capacity assessments.

Main Methods:

• Fourteen male soldiers performed maximal box lifting and repetitive lift and carry tasks with varying loads (17.5-37.5 kg).
• Linear mixed models were used to analyze the relationships between carry mass, endurance duration, and oxygen consumption.
• Individual variations in endurance were accounted for using random effects.

Main Results:

• Endurance time was inversely related to carry mass (R²=0.24), with substantial individual differences (R²=0.85).
• Normalizing carry mass to maximal lifting performance enhanced endurance time prediction (R²=0.40).
• Oxygen consumption, relative to total mass, did not significantly correlate with lift and carry mass.

Conclusions:

• Findings provide practical data for establishing work-rest schedules in repetitive manual handling.
• The study offers insights into methods for assessing the physical capacity of workers in manual handling roles.