Obesity changes how joints bear weight during lifting, especially with light loads.

Lifting heavy items at work can lead to muscle and bone injuries, and obesity raises this risk. Researchers wanted to see how body mass index, or BMI, alters the physical stress placed on the body during lifting and moving items. When you pick up a box, your joints act like pivot points. Your muscles must produce turning forces, called joint momentsjoint momentsA measure of the turning force or strain at a joint, like how hard muscles have to pull., to move your bones. The researchers discovered that a higher BMI caused larger forces in the lower back and shoulders. Surprisingly, these back forces grew the most during lifts from the floor, during lighter loads, and especially in males. Because workers barely changed their posture, extra body mass was the key factor driving up stress on their joints.

Why it matters

People with obesity face a higher risk of work-related injuries from lifting and carrying. This study shows that the extra strain on the spine and shoulders doesn't simply scale with body weight—it depends on the task, the load, and even gender. That means safety guidelines must be tailored to body size and specific job demands, rather than using one-size-fits-all rules.

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