Blade size and weight effects in shovel design

Area of Science:

• Ergonomics and Human Factors
• Biomechanics
• Occupational Health

Background:

• Shovels are fundamental tools with minimal design evolution.
• Previous research identified effects of shovel weight and blade size, but lacked quantification of their interplay.
• Understanding the optimal trade-off is crucial for improving shoveling efficiency and reducing physical strain.

Purpose of the Study:

• To quantify the relationship between shovel weight and blade size in relation to energy expenditure and performance.
• To determine the optimal blade-size/shovel-weight ratio for efficient sand shoveling.
• To assess user preference based on perceived exertion.

Main Methods:

• Five subjects performed sand shoveling tasks using five different shovels with varied blade sizes and weights.
• Measurements included energy expenditure, heart rate, ratings of perceived exertion, and shoveling performance.
• Energy expenditure was normalized to subject weight and load handled.

Main Results:

• Normalized energy expenditure showed a quadratic relationship with the blade-size/shovel-weight (B/W) ratio.
• The minimum energy cost occurred at a B/W ratio of 0.0676 m²/kg, corresponding to an acceptable energy expenditure of 5.16 kcal/min.
• Subjects preferred lighter shovels, irrespective of blade size, and perceived heavier shovels or oversized blades as increasing energy expenditure.

Conclusions:

• The optimal shovel design balances blade size and weight to minimize energy expenditure for tasks like sand shoveling.
• Deviations from the optimal B/W ratio, either too large a blade or too heavy a shovel, increase energy costs.
• User preference aligns with lighter tools, suggesting that perceived exertion is a significant factor in tool selection and efficiency.