ROTATIONAL MOTION

From a historical point of view, helmets have been designed to protect against energies and forces arising from a linear influence, with the principle aim of protecting against skull fractures, which is mirrored in current regulatory certification standards that at present do not take into account rotational motion from an angled impact to the head. However, the human brain is more sensitive to rotational motion than linear movements.

Rotational motion is a result of an angled impact to the head and is a combination of rotational energy (angular velocity) and rotational forces (from angular acceleration). This rotational motion results in shearing and/or stretching of brain tissue which affects the brain and increases the risk of both minor and more severe brain injuries. Research has shown that the most common severe brain injuries like Diffuse Axonal Injury (DAI) and Subdural Hematoma (SDH) arise more easily when the head is subjected to rotational motion. Similar research has shown that it is very likely that rotational motion causes concussion or mild traumatic brain injury more than straight impact.

MIPS has noticed an increased awareness of the importance of protection from rotational motion. The growing awareness can be exemplified by an increased focus from organisations’ and regulatory bodies’ working groups on helmet standards. Furthermore, more than 60 helmet brands around the world used MIPS BPS in their helmet models in 2017, which points to an increased brand and consumer awareness when it comes to protection from rotational motion.

Several working groups, linked to organisations and regulatory bodies, which in various ways influence helmet standards, are increasingly discussing the effects of rotational motion and various ways of incorporating protection from rotational motion in the helmet standards. Examples of working groups are:

    • CEN TC158 – WG11
    • NOCSAE new test method for American football helmets
    • FIM Helmet Certification Program (FHCP)

    This increased focus on the subject has been especially visible over recent years.

    Proof of the increased awareness about protection from rotational motion is the fact that certain consumer tests have started including protection from angled impacts in their methods of comparing different helmets. Folksam, the Swedish insurance company, which conducts an annual test of bicycle helmets, started to include protection from angled impacts to the head in their evaluation in 2012. In addition, Consumer Report, a non-profit-making organization based in the US that conducts tests and comparisons, started to include angled impacts to the head in their bicycle helmet tests during 2016. These comparative consumer studies have been supplemented by scientific publications where, for instance, a research team from the Vehicle Safety Institute at the Graz University of Technology, Austria, has compared six bicycle helmets (one fitted with MIPS BPS) and conducted tests including measurements of rotational motion that have been transmitted to the brain.

    – MCELHANEY J. H., ROBERTS V. L., HILYARD J. F. (1976). “PROPERTIES OF HUMAN TISSUES AND COMPONENTS: NERVOUS TISSUES,” I HANDBOOK OF HUMAN TOLERANCE (TOKYO: AUTOMOBILE RESEARCH INSTITUTE INC)
    – GENNARELLI T. A., THIBAULT L. E., TOMEI G., WISER R., GRAHAM D. I., ADAMS J. (1987). “DIRECTIONAL DEPENDENCE OF AXONAL BRAIN INJURY DUE TO CENTROIDAL AND NON-CENTROIDAL ACCELERATION,” I PROCEEDINGS OF THE 31ST STAPP CAR CRASH CONFERENCE (WARRENDALE, PA: SOCIETY OF AUTOMOTIVE ENGINEERS)
    – HTTP://WWW.SIS.SE/NYHETER-OCH-PRESS/NYHETER/NY-PROVNINGSMETOD-FOR-HJALMAR/
    – NOCSAE DOC (ND)002-16, HTTP://NOCSAE.ORG/WP-CONTENT/FILES_MF/1451499468ND00216MFRDFBHELMETSSTANDARDPERFORMANCE.PDF
    – HTTP://WWW.FIM-LIVE.COM/EN/ARTICLE/FIM-HELMET-CERTIFICATION-PROGRAMME
    – KLUG C, FEIST F, TOMASCH E, TESTING OF BICYCLE HELMETS FOR PREADOLESCENTS, PROCEEDING OF IRCOBI CONFERENCE 2015