Current equestrian helmet standards may not adequately represent real-world concussive impacts in horse sport, according to researchers.
Biomechanical engineer Michio Clark and his fellow researchers suggest there is an urgent need to assess the protective capacity of equestrian helmets under real-world conditions.
The research team set about examining the biomechanics involved in a series of actual horse accidents in a University College Dublin study reported in the Journal of Science and Medicine in Sport.
Equestrian helmets are designed to pass certification standards based on linear drop tests onto rigid steel surfaces. These drops result in almost instantaneous decelerations, resulting in a massive, albeit brief, spike in g forces.
While fighter pilots might experience accelerations of 8 g or more while flying, the near-instantaneous accelerations resulting from a helmet deceleration on impact are much greater.
Current standards commonly require helmets to meet a threshold of 250 g in a drop on to a steel anvil, which results in impacts lasting less than 15 milliseconds.
But Clark and his colleagues, who examined falls from horse-racing and the cross-country phase of Eventing, found that most concussions occur when a rider is thrown from their mount and obliquely strikes a compliant surface such as turf or sand.
In equestrian sports, the risk of impacting rigid surfaces would only arise for impacts with the likes of a horse’s hoof, concrete surfaces, or a fence.
For the study, video and corresponding accident data from 1119 falls were collected from governing bodies in Ireland and Britain.
Twenty-five concussive and 25 non-concussive falls, involving men and women, were identified as being suitable for the study.
These falls were reconstructed using a combination of video analysis, computational and physical reconstruction methods.
The authors evaluated the head impact location, the impact surface, the horizontal velocities involved, the height of the rider’s head, and the rider’s body position prior to impact.
The experimental reconstructions were conducted in a laboratory setting using a helmeted headform commonly used in accident reconstruction, and a rail-guided launcher.
Three representative anvils was used to reflect the different impact surface for each accident and three impact tests were conducted for each case. This gave the study team data on linear acceleration (g’s) rotational velocity and rotational acceleration.
They calculated the various thresholds for these factors which resulted in a 50% chance of a rider being concussed.
These thresholds for linear acceleration, rotational velocity and rotational acceleration were described by the study team as a unique combination of head kinematic thresholds when compared to other sports.
Rotational velocity thresholds were similar to those reported for American football and Australian Rules football and rugby, while the linear acceleration threshold was at the lower end of reported sporting thresholds, at 59 g.
“Compared to concussive thresholds for ice hockey collisions, the linear acceleration threshold of this study was higher but the rotational acceleration threshold was similar.”
They said the unique combination of head kinematics was a direct consequence of equestrian head impacts tending to be oblique falls on to a compliant surface.
“As such, these 50 reconstructed equestrian accidents constitute an important contribution to the growing body of real-world head injury accidents.
“The low magnitude rotational accelerations and long durations (more than 20 milliseconds) are a reflection of the compliant impact surfaces, whereas the relatively high magnitude linear accelerations for the given impact duration were a reflection of the large amount of energy transferred to the head during falls.”
As expected, concussions were associated with higher impact speeds. “Clearly, for all else being equal, faster impact velocities result in higher head kinematics and brain tissue responses and subsequently increase the risk of injury.
“It was also unsurprising that impact velocity was found to be the best predictor of concussion.”
Impact velocity represented the fundamental difference between concussive and non-concussive cases, they said, as greater levels of impact energy correspond to greater risks of concussion.
They said that while decreasing impact velocity may not be a practical design solution for equestrian sports and horse racing, fall techniques are often taught in combat sports and gymnastics as injury prevention strategies.
However, they acknowledge that falls in equestrian sports do not always allow riders sufficient reaction time before impact.
Further management of impact velocity in Eventing could be achieved by modifying the rules for course completion times.
“The results of this study also have significant implications for equestrian helmet standards and helmet designs,” they said.
In conclusion, concussive accidents associated with an oblique impact to a compliant surface resulted in considerably lower accelerations (less than 130 g) than the commonly used 250 g threshold in current equestrian standards.
The concussive accidents also had considerably longer impact durations than current equestrian helmet standard impacts, which are less than 15 milliseconds.
“This indicates that the current equestrian helmet standards and design tests do not properly account for the loading conditions associated with concussion.
“Consequently, the performance of equestrian helmets under real-world accident loading conditions is currently unknown.”
They suggest that future work should aim to assess the protective capacity of equestrian helmets for oblique impacts to a compliant anvil and the use of appropriate injury threshold values similar to those reported in this study when assessing the risk of concussion.
“From the accident reconstructions, it is apparent that current certification standards for equestrian helmets represent different loading conditions than those associated with real-world concussion.
“It is unknown how equestrian helmets perform for oblique impacts to a compliant surface and, therefore, there is a need to assess the protective capacity of equestrian helmets under these impact loading conditions.”
The study team comprised Clark, Aisling Ni Annaidh and Michael Gilchrist, all with University College Dublin; Andrew Post, Blaine Hoshizaki and Kevin Adanty, with the University of Ottawa; Jonathan Clissold, with British Eventing; Adrian McGoldrick with the Irish Horseracing Regulatory Board; and Jerry Hill, with the British Horseracing Authority.
Proposed injury thresholds for concussion in equestrian sports
Clark, J. Michio et al.
Journal of Science and Medicine in Sport, Volume 23, Issue 3, 222-236 https://doi.org/10.1016/j.jsams.2019.10.006