Tag Archives: angular acceleration

Angular acceleration Dr. John Lloyd has served attorneys nationwide for 25+ years in biomechanics, human factors, helmet testing and motorcycle accident expert

Research article “Brain Injury in Sports” published in Journal of Neurosurgery

Dr. Lloyd is pleased to announce that his research article  on Sports Brain Injury, co-authored with Dr. Frank Conidi has been published in the Journal of Neurosurgery:

Lloyd - Sports Brain Injury

OBJECT
Helmets are used for sports, military, and transportation to protect against impact forces and associated injuries. The common belief among end users is that the helmet protects the whole head, including the sports brain injury. However, current consensus among biomechanists and sports neurologists indicates that helmets do not provide significant protection against concussion and sport brain injury. In this paper the authors present existing scientific evidence on the mechanisms underlying traumatic head and sports brain injury, along with a biomechanical evaluation of 21 current and retired football helmets.

METHODS
The National Operating Committee on Standards for Athletic Equipment (NOCSAE) standard test apparatus was modified and validated for impact testing of protective headwear to include the measurement of both linear and angular kinematics. From a drop height of 2.0 m onto a flat steel anvil, each football helmet was impacted 5 times in the occipital area.

RESULTS
Skull fracture risk was determined for each of the current varsity football helmets by calculating the percentage reduction in linear acceleration relative to a 140-g skull fracture threshold. Risk of subdural hematoma was determined by calculating the percentage reduction in angular acceleration relative to the bridging vein failure threshold, computed as a function of impact duration. Ranking the helmets according to their performance under these criteria, the authors determined that the Schutt Vengeance performed the best overall.

CONCLUSIONS
The study findings demonstrated that not all football helmets provide equal or adequate protection against either focal head injuries or traumatic brain injuries. In fact, some of the most popular helmets on the field ranked among the worst. While protection is improving, none of the current or retired varsity football helmets can provide absolute protection against brain injuries, including concussions and subdural hematomas. To maximize protection against head and brain injuries for football players of all ages, the authors propose thresholds for all sports helmets based on a peak linear acceleration no greater than 90 g and a peak angular acceleration not exceeding 1700 rad/sec2.

http://thejns.org/doi/abs/10.3171/2014.11.JNS141742

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Motorcycle Accident Expert in Biomechanics and Human Factors

Motorcycle Accident Expert

Motorcycle collision analysis is a highly specialized discipline in which Dr. Lloyd is eminently qualified as a motorcycle accident expert. In addition to holding a PhD in Ergonomics (Human Factors), with a specialization in Biomechanics, John has more that 20 years and 200,000 miles of experience riding motorcycles. John-Lloyd-motorcycle-accident-expertDr. Lloyd has completed numerous advanced programs, including Motorcycle Safety Foundation (MSF), Experienced Rider Course and Total Rider Tech Advanced training.

Motorcycle Helmets and Brain Injury

To consider whether a motorcycle helmet might reduce the risk of brain trauma in a motorcycle accident it is first important to understand the two primary mechanisms associated with traumatic brain injury – impact loading and impulse loading.

Impact loading involves a direct blow transmitted primarily through the center of mass of the head, resulting in extracranial focal injuries, such as contusions, lacerations and external hematomas, as well as skull fractures. Shock waves from blunt force trauma may also cause underlying focal brain injuries, such as cerebral contusions, subarachnoid hematomas and intracerebral hemorrhages. Whereas, impulse or inertial loading caused by sudden movement of the brain relative to the skull, produces cerebral concussion. Inertial loading at the surface of the brain can cause subdural hemorrhage due to bridging vein rupture, whereas if affecting the neural structures deeper within the brain can produce diffuse axonal injury (DAI).

Holbourn was the first to cite angular / rotational acceleration as an important mechanism in brain injury. Gennarelli, Thibault, and colleagues, in a series of studies using live primates and physical models investigated the role of rotational acceleration in brain injury. They concluded that angular acceleration contributes more than linear acceleration to brain injuries, including concussion, axonal injury, and subdural hematoma.

Motorcycle Helmet Testing

Traditional testing of motorcycle helmets focuses on reducing the effect of linear impact forces by dropping them from a given height onto an anvil and measuring the resultant peak linear acceleration. According to the Federal Motor Vehicle Safety Standard (FMVSS) 218, commonly known as the DOT helmet standard, the test involves dropping a motorcycle helmet onto a flat steel and hemispherical anvil at an impact velocity of 6.0 m/s (13.4mph).   In general, if peak linear acceleration is less than 400g, the helmet is considered acceptable. Current motorcycle helmet testing standards do not incorporate measures of angular acceleration and therefore do not address whether any helmets can provide adequate protection against catastrophic brain injuries, such as concussion, axonal injury and subdural hematoma.

In 1995, the European Commission Directorate General for Energy and Transport initiated a Cooperative Scientific and Technical Research (COST) program to investigate Motorcycle Safety Helmets. Several agencies from Finland, the United Kingdom, France and Germany participated in this study, which compiled and analyzed data from 4,700 motorcycle fatalities in Europe, each year. The COST report [i] documents that 75% of all fatal motorcycle accidents involve head injury. Linear forces were present in only 31% of fatal head injuries, while rotational forces were found to be the primary cause in over 60% of cases. Within the scope of this study experiments were performed using drop tests with accelerometers to measure linear and rotational accelerations of the brain and skull mass associated with different types of impacts. These tests confirmed rotational acceleration to be a primary cause of brain injury in helmeted motorcycle accidents.

John-Lloyd-motorcycle-accident-expert-helmet

  • Rotational forces acting on the brain are the underlying cause of traumatic brain injuries.
  • Motorcycle helmets, including those certified under DOT and SNELL standards are designed to mitigate forces associated with linear acceleration.
  • Motorcycle helmets are not currently certified under either DOT or SNELL standard against their ability to protect against the angular / rotational forces.
  •  Epidemiologic evidence from the COST-327 report  indicates that motorcycle helmets do not provide adequate protection against closed head and brain injuries

Human Factors of Motorcycle Accidents

Human factors in vehicle collisions include all factors related to drivers and other road users that may contribute to a collision. Examples include driver behavior, visual and auditory acuity, decision-making ability, and reaction speed. A 1985 report based on British and American crash data found driver error, intoxication and other human factors contribute wholly or partly to about 93% of crashes.

Motorcycle Inspection

Motorcycle accident analysis often requires involves a teardown and careful inspection of the machine to investigate for possible contributing factors. Our engineers have a combined 70 years experience with motorcycle mechanics.

John Lloyd motorcycle accident expert inspection

A thorough evaluation includes inspection of tires, brakes, suspension setup, electrical components as well as any aftermarket parts.

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NI Week features John Lloyd football helmet expert

Football helmet expert, Dr. John Lloyd,  had the privilege to present his research on football helmets as part of the Keynote address at the National Instrument conference in Austin, TX this week. The audience of 5,000+ attendees learned about Dr. Lloyd’s research into biomechanics of the brain.

 

It has been said that helmets cannot prevent concussions. I disagree.

As a biomechanist I have dedicated my career to studying the biomechanics of brain injuries. There are two key mechanical forces that give rise to head and brain injuries (1) linear forces, which are responsible for visible injuries, including bruising and skull fractures, and (2) rotational forces, which cause invisible injuries, such as concussion and brain injury.

Since helmets are currently designed to pass testing standards that focus on linear forces only, it is no surprise that helmets have limited benefit in preventing concussions. Through advances in medicine we have learned that concussions can potentially have life-long neurological consequences, including memory impairement and personality changes / behavioral effects.

Over the past years I have developed and validated a testing method to evaluate helmets in terms of their ability to protect against both linear and rotational forces. Using this apparatus I characterized football helmets, results of which have been submitted to Science for publication.

Based on lessons learned from my biomechanical evaluation of various sports helmets, I have devised a matrix of shear-thickening non-Newtonian materials. A prototype helmet was constructed using this matrix liner, results of which show that rotational forces that cause concussion and other brain injuries are reduced by up to 50% compared to a leading football helmet, while also reducing linear forces.

Football helmet expert Dr. John Lloyd

helmet prototype reduces concussion risk

It is my goal and my passion to work with leading helmet companies to make this technology available to players and sports participants of all aged to enhance their protection against brain trauma. I am looking to collaborate with one manufacturer in each sport to offer an exclusive license patent-pending technology.

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