Rotational motion

Historically, helmets have been designed to protect against linear motion, with the principle aim of protecting against skull fractures. This is mirrored in current regulatory certification standards. However oblique impact is a more common accident scenario and most regulatory standards does not certify helmets against those impacts, even though research show that the human brain is more sensitive to rotational motion than linear motion.

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 140 helmet brands around the world used Mips safety system in their helmet models in 2021, 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
– FIM Helmet Certification Program (FHCP)
– CPSC Consumer Product Safety Commision
– ECE 22.06 Economic Commission for Europe

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 for example the American test insitute, Virginia Tech. Folksam and Länsförsäkringar, Swedish insurance companies, which conducts annual tests of bicycle helmets, started to include protection from angled impacts to the head in their evaluation in 2012.