How Are Bicycle Helmets Designed to Prevent Head Injuries?

Patient Presentation
A pediatrician was bike riding with her teenage son when she hit a rock, lost balance, and fell off her bike onto concrete pavement landing on her back. Her head hit quite hard and there was a loud “cracking” sound heard. Surprising she was only hurt on her hip slightly but had no other pain and was conscious throughout the event. Her son helped her to take off her helmet as she was sitting to catch her breath and exclaimed, “Wow you really hit hard. Look at the crack in your helmet! That must have been that loud sound. Wow!” When they returned home, she noticed that the plastic shell covering on his helmet was also damaged and asked him about it. “Oh, I noticed that before but its just decoration so I didn’t think it was important,” he answered. She informed him that the plastic shell wasn’t just decoration and needed to be replaced if it was cracked too. Two new helmets were purchased and the damaged ones were placed in the garbage.

Yellow arrows indicates damage.
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Figure 123a – Exterior view of crack in bike helmet foam.

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Figure 123b – Close of view of crack in bike helmet foam.

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Figure 123c – Exterior view of crack in bike helmet foam.

Protective helmets are used for multiple occupational and recreational activities. They are designed to protect the head from the common problems associated with the activity. For example, hard hats for construction workers are meant to protect against superior and lateral objects contacting the head as something can fall from above or a worker may contact an object as they are moving. The helmet had a plastic suspension ring that sits on the head providing space between the plastic helmet and the head allowing for the striking force to be dissipated over that distance before the helmet contacts the head. Helmets are designed for a specific purpose therefore are not appropriate for other activities. Information about various protective helmets can be found here.

Bicycle riding is a great physical activity for individuals, families and groups. It is also a great activity for people of any age and modified bicycles are available for many people with disabilities. However any activity involves some risks including bike riding. In 2015 in the US, 818 bicyclists died, an increase of 12.2%. An additional 45,000 were reported injured. For children < 14 years of age, 44 died and 5000 were injured. Many cyclists (27%) who died had been drinking and 37% of motor vehicle/cycle crashes involved either the driver or cyclist drinking. Fatalities and injuries occurred more often during darkness hours too.

The National Highway Transportation Safety Administration notes:

  • “Bicyclists are considered vehicle operators; they are required to obey the same rules of the road as other vehicle operators, including obeying traffic signs, signals, and lane markings. When cycling in the street, cyclists must ride in the same direction as traffic.” Bike riding can be a very good introduction for children to learn motor vehicle driving rules even at a young age.
  • “Bicyclists should increase their visibility to drivers by wearing fluorescent or brightly colored clothing during the day, and at dawn and dusk. To be noticed when riding at night, use a front light and a red reflector or flashing rear light, and use retro- reflective tape or markings on equipment or clothing.”
  • “All bicyclists should wear properly fitted bicycle helmets every time they ride. A helmet is the single most effective way to prevent head injury resulting from a bicycle crash.”

Bike helmets are important to protect the head from injury. They must be properly fitted to maintain their protective effect. Fitting should be checked before each ride and readjusted as necessary. The helmet should also be checked that there are no parts broken or missing before each ride. For more information about properly fitting bike helmets, see here and here. The “best” bicycle helmet depends on many factors which can be reviewed here.

Learning Point
Bike helmets are designed with 3 major components:

  • Foam interior – this is the most important part of the helmet. It is usually made of extruded polystyrene foam and designed to compress under the force and distribute the force over more of the head.
  • Plastic shell – this is designed to allow the head to slide or skid on the ground. Remember there are items on the ground which can catch on the helmet and cause rotational or torque to the head and neck. The shell also helps to keep the foam intact.
  • Straps and buckles – the helmet must be secured to the head and remain in place during a crash for full effect.

Remember if ANY part of the helmet is broken (this includes buckle parts) then the helmet needs to be replaced. Parents and children should inspect the helmet and adjust fittings before each ride. Also remember bike helmets are designed for biking – they are not designed for other activities and appropriate protective helmets and other protective gear designed for the activity should be used. Children should be taught that bike helmets are to be used when biking only and to be taken off when done. They should not continue to be worn when playing on playgrounds, climbing trees, etc. Children should be taught that a bike helmet goes on before the wheels move and taken off when the wheels stop.

Questions for Further Discussion
1. What other recreational activities require helmets for protection and how are they different from bike helmets?
2. How are car seats and bike helmets similar in design and use?

Related Cases

To Learn More
To view pediatric review articles on this topic from the past year check PubMed.

Evidence-based medicine information on this topic can be found at, the National Guideline Clearinghouse and the Cochrane Database of Systematic Reviews.

Information prescriptions for patients can be found at MedlinePlus for these topics: Sports Safety and Exercise and Physical Fitness.

To view current news articles on this topic check Google News.

To view images related to this topic check Google Images.

To view videos related to this topic check YouTube Videos.

National Highway Transportation Safety Administration. Traffic Safety Facts Bicyclists and Other Cyclists.
Available from the Internet at (rev. March 2017, cited 7/24/18).

Bicycle Helmet Safety Institute. Helmets: How they Work, and What Standards Do.
Available from the Internet at (rev. 10/18/2017, cited 7/24/18).

Consumer Product Safety Commission. Bicycle Helmets Business Guidance
Available from the Internet at–Manufacturing/Business-Education/Business-Guidance/Bicycle-Helmets (cited 7/24/18).

Donna M. D’Alessandro, MD
Professor of Pediatrics, University of Iowa