Comparing Equestrian Helmets with and without Rotational Technology Using an Equestrian Concussive Specific Helmet Test Protocol

Abstract

Horse riding is a popular global activity involving a wide range of sporting events including dressage, endurance riding, eventing, show jumping, horse racing and rodeo. Unfortunately, horse riding and equestrian sporting events, report a high prevalence of concussion. The most common mechanism for brain injury in equestrian events involve high levels of linear and rotational acceleration during head impacts when falling from a horse. These accelerations create injurious brain tissue strain. While both linear and rotational accelerations occur during head impacts, the rotational components of acceleration are closely linked to brain tissue strain. To reduce brain strain, helmet technologies have been developed with the aim to reduce head rotational accelerations during an impact. The most common rotational managing technology, multi-directional impact protection system (MIPS), employs a low friction layer to reduce the amount of rotational acceleration sustained by the brain during head impacts. MIPS tests equestrian helmets using a monorail drop rig with a 45-degree steel anvil covered in 80 grit sandpaper at 6.2 m/s. The surface experiencing impact in the MIPS test method is a very low compliant surface (steel). It is impacted at a velocity of 6 m/s, and an anvil angle of 45-degrees. In contrast, most impacts in equestrian involve high compliant material such as sand or turf with an average impact velocity is 9 m/s, and the average angle of impact of 27 degrees. The proposed rotational testing method employed by MIPS may not fully represent the most common accidents involving equestrian events. The objective of this research was to evaluate the effectiveness of a helmet with rotational technology to reduce linear and rotational acceleration, rotational velocity, and maximum principal strain (MPS) in equestrian helmets. An equestrian specific test protocol was developed using the common impact conditions for concussive events for equestrian riders. Nine m/s impact velocity, with an angle of 26.5 degrees to the horizontal axis, and an anvil compliance consisting of 66 mm of 602 vinyl nitrile foam with synthetic grass to represent turf impacts was reported as the most common impact characteristics. Using a Rail Guided Launcher, a helmeted Hybrid III headform was launched and impacted a low and high compliance anvil using the defined velocity and angle parameters. Two equestrian helmet types were impacted, a conventional helmet with no rotational technology and the same helmet model with rotational technology. The impact locations tested included front, side, and rear boss, as these were the most common impact locations reported for concussive events in equestrian. Linear and rotational acceleration and rotational velocity were measured using a DTS SLICE sensor installed inside the headform. The linear and rotational acceleration curves were then used as input to the University College Dublin Brain Trauma Model (V2.0) to calculate MPS. Statistical analysis included four t-tests, two 2x2x3 ANOVA's with 8 pairwise Tukey post-hoc test, significance set to α=0.05. The results were not uniform across impact locations and anvil compliances, the rear boss impact location in helmets with rotational technology revealed significantly lower rotational accelerations and rotational velocity. The results revealed helmets with rotational technology should be designed to perform under these high-energy conditions. If the rotational technology was designed with these considerations, it would be possible to investigate the potential of rotational technologies to decrease dynamic head response and the brain tissue strain.