Effect of task variables and their interactions in lifting and lowering loads

Area of Science:

• Ergonomics and Human Factors
• Occupational Health and Safety
• Physiological Measurement

Background:

• Manual materials handling (MMH) tasks are a common cause of workplace injuries.
• Understanding the physiological demands of MMH is crucial for designing safer work practices.
• Previous research has explored various factors influencing MMH, but interactions between variables require further investigation.

Purpose of the Study:

• To investigate the effects of multiple task variables on metabolic energy expenditure and heart rate during lifting and lowering.
• To determine the influence of container dimensions and handle presence on physiological responses.
• To assess changes in subject strength following a period of MMH training.

Main Methods:

• Four male subjects performed controlled lifting and lowering tasks with varying loads, frequencies, heights, and container dimensions.
• Metabolic energy expenditure (oxygen uptake) and heart rate were continuously monitored.
• Subject strength was measured before and after the seven-week experimental period.
• Analysis of variance (ANOVA) was used to analyze the data for lifting and lowering tasks separately.

Main Results:

• Load, frequency, height, container width, and container length significantly affected metabolic energy expenditure and heart rate (p <= 0.01).
• Container height and the presence/absence of handles did not significantly impact physiological responses for lowering tasks.
• Significant first and second-order interactions were observed among the task variables.
• Subjects showed a significant increase in strength (p <= 0.025) after seven weeks of MMH activities.
• Dimensional sensitivity analysis revealed that box width was more critical than length up to 0.56m.

Conclusions:

• Task variables like load, frequency, and container dimensions are critical determinants of physiological strain during MMH.
• Interactions between these variables play a significant role in the overall metabolic cost.
• MMH training can lead to measurable improvements in physical strength.
• Ergonomic interventions should consider the interplay of load, frequency, and container dimensions for optimal safety and efficiency.