Canadian Centre for Occupational Health and Safety
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Health and Safety: Teaching Tools

Posture and Force

Purpose: To demonstrate an ergonomic problem.

Materials required: Two boxes with equal weight (light) - one long rectangular box without handles and one square, compact box with good handles.

Instructions: Learners are asked to lift both boxes from the floor to a table using two different lifting techniques - a stoop posture (straight legs), and a squat (bent knees) posture. They are asked to describe how they felt about each lifting situation - which was easier and why (box size, handles and posture used to lift).

Expected Results: The intent is to get your learners to see what makes a better lift, what makes an awkward lift, and how posture and size can change the force demand without changing the weight. The awkward box that was lifted using a stoop posture (straight legs) is the poorest method of lifting and should be reflected in the student's comments.

Stoop method

Squat method

When discussing the two methods of lifting with the students you should also identify that when comparing the two methods of lifting, the stoop method actually uses less overall energy then the squat method. This is why people tend to use the stoop method, or start lifting with the stoop method over time. In the long run, although you are using less energy with the stoop method, you are actually using poor posture and excessive force over the pivot point in the back. This causes localized fatigue in the back muscles and increases the risk for back injury. Overall, using the squat method will protect them from injury, and will decrease soreness and tenderness after periods of excessive lifting.