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(HealthDay News) -- Helmets can prevent serious injuries on the football field, and from bicycles, skateboards, and scooters.

But for the helmet to work, the American Academy of Orthopaedic Surgeons says, it must fit properly.

To find a proper fit, you may need to try several sizes and models. Helmets should be worn flat on your head and low on your forehead, with the bottom edge parallel to the ground. Side straps should form a V shape around the ear, and the buckle should fasten tightly.

The device should also contain pads that can be removed or installed for a perfect fit. Most important, the helmet should not move in any direction when you shake your head, or interfere with vision, movement or hearing.

Helmets should be replaced when they are damaged, outgrown or at least every five years.