Cynthia Bir

Biomechanics of the head for Olympic boxer punches to the face

Objective: The biomechanics of the head for punches to the jaw and the risk of head injury from translational and rotational acceleration were studied. Methods: Seven Olympic boxers from five weight classes delivered 18 straight punches to the frangible face of the Hybrid III dummy. Translational and rotational head acceleration, neck responses, and jaw pressure distribution were measured. High speed video recorded each blow and was used to determine punch velocity. Equilibrium was used to determine punch force, energy transfer, and power. Results: Punch force averaged 3427 (standard deviation (SD) 811) N, hand velocity 9.14 (SD 2.06) m/s, and effective punch mass 2.9 (SD 2.0) kg. Punch force was higher for the heavier weight classes, due primarily to a higher effective mass of the punch. Jaw load was 876 (SD 288) N. The peak translational acceleration was 58 (SD 13) g, rotational acceleration was 6343 (SD 1789) rad/s2, and neck shear was 994 (SD 318) N. Conclusions: Olympic boxers deliver straight punches with high impact velocity and energy transfer. The severity of the punch increases with weight class.

Intracarpal canal pressures: the role of finger, hand, wrist and forearm position

OBJECTIVE: The study examined the change in intracarpal canal pressure (ICCP) in relationship to finger, hand, wrist and forearm position. DESIGN: The study was an in vivo measurement of ICCP in seven subjects undergoing a standardized set of manoeuvres that systematically varied finger, hand, wrist, and forearm position. BACKGROUND: It has been known that the ICCP increased with extremes of wrist flexion and extension but the change in pressure in response to radial and ulnar deviation as well as hand and forearm position has not been reported. METHODS: The ICCP was measured using a slit catheter technique; each variation of position was repeated three times with continuous monitoring of ICCP, wrist angulation, and metacarpal-phalangeal joint angulation. RESULTS: The study demonstrated that ICCPs were lowest when the wrist is in a neutral position, the hand relaxed with fingers flexed and the forearm in a semi-pronated position. Wrist extension and flexion resulted in the greatest increase in ICCP followed by forearm pronation and supination. Radial and ulnar deviation also increased the pressure but to a lesser extent. CONCLUSIONS: The findings of this study support the concept that the wrist and forearm should be maintained in a neutral position during vocational and avocational activities in an effort to minimize pressure within the carpal tunnel and thereby reduce the risk of developing carpal-tunnel syndrome. RELEVANCE: It is desirable to know how the ICCP changes in response to change in hand, wrist, and forearm position so that work activities are designed to minimize the pressure within the carpal canal and thus maintain the viability of the median nerve within the carpal canal.

Concussion in professional football: comparison with boxing head impacts--part 10.

OBJECTIVE: This study addresses impact biomechanics from boxing punches causing translational and rotational head acceleration. Olympic boxers threw four different punches at an instrumented Hybrid III dummy and responses were compared with laboratory-reconstructed NFL concussions. METHODS: Eleven Olympic boxers weighing 51 to 130 kg (112–285 lb) delivered 78 blows to the head of the Hybrid III dummy, including hooks, uppercuts and straight punches to the forehead and jaw. Instrumentation included translational and rotational head acceleration and neck loads in the dummy. Biaxial acceleration was measured in the boxer’s hand to determine punch force. High-speed video recorded each blow. Hybrid III head responses and finite element (FE) brain modeling were compared to similarly determined responses from reconstructed NFL concussions. RESULTS: The hook produced the highest change in hand velocity (11.0 ± 3.4 m/s) and greatest punch force (4405 ± 2318 N) with average neck load of 855 ± 537 N. It caused head translational and rotational accelerations of 71.2 ± 32.2 g and 9306 ± 4485 r/s2. These levels are consistent with those causing concussion in NFL impacts. However, the head injury criterion (HIC) for boxing punches was lower than for NFL concussions because of shorter duration acceleration. Boxers deliver punches with proportionately more rotational than translational acceleration than in football concussion. Boxing punches have a 65 mm effective radius from the head cg, which is almost double the 34 mm in football. A smaller radius in football prevents the helmets from sliding off each other in a tackle. CONCLUSION: Olympic boxers deliver punches with high impact velocity but lower HIC and translational acceleration than in football impacts because of a lower effective punch mass. They cause proportionately more rotational acceleration than in football. Modeling shows that the greatest strain is in the midbrain late in the exposure, after the primary impact acceleration in boxing and football.

Concussion in professional football: helmet testing to assess impact performance--part 11

OBJECTIVE:National Football League (NFL) concussions occur at an impact velocity of 9.3 ± 1.9 m/s (20.8 ± 4.2 mph) oblique on the facemask, side, and back of the helmet. There is a need for new testing to evaluate helmet performance for impacts causing concussion. This study provides background on new testing methods that form a basis for supplemental National Operating Committee on Standards for Athletic Equipment (NOCSAE) helmet standards. METHODS:First, pendulum impacts were used to simulate 7.4 and 9.3 m/s impacts causing concussion in NFL players. An instrumented Hybrid III head was helmeted and supported on the neck, which was fixed to a sliding table for frontal and lateral impacts. Second, a linear pneumatic impactor was used to evaluate helmets at 9.3 m/s and an elite impact condition at 11.2 m/s. The upper torso of the Hybrid III dummy was used. It allowed interactions with shoulder pads and other equipment. The severity of the head responses was measured by a severity index, translational and rotational acceleration, and other biomechanical responses. High-speed videos of the helmet kinematics were also recorded. The tests were evaluated for their similarity to conditions causing NFL concussions. Finally, a new linear impactor was developed for use by NOCSAE. RESULTS:The pendulum test closely simulated the conditions causing concussion in NFL players. Newer helmet designs and padding reduced the risk of concussion in 7.4 and 9.3 m/s impacts oblique on the facemask and lateral on the helmet shell. The linear impactor provided a broader speed range for helmet testing and more interactions with safety equipment. NOCSAE has prepared a draft supplemental standard for the 7.4 and 9.3 m/s impacts using a newly designed pneumatic impactor. No helmet designs currently address the elite impact condition at 11.2 m/s, as padding bottoms out and head responses dramatically increase. CONCLUSIONS:The proposed NOCSAE standard is the first to address helmet performance in reducing concussion risks in football. Helmet performance has improved with thicker padding and fuller coverage by the shell. However, there remains a challenge for innovative designs that reduce risks in the 11.2 m/s elite impact condition.

Intracranial pressure increases during exposure to a shock wave

Traumatic brain injuries (TBI) caused by improvised explosive devices (IEDs) affect a significant percentage of surviving soldiers wounded in Iraq and Afghanistan. The extent of a blast TBI, especially initially, is difficult to diagnose, as internal injuries are frequently unrecognized and therefore underestimated, yet problems develop over time. Therefore it is paramount to resolve the physical mechanisms by which critical stresses are inflicted on brain tissue from blast wave encounters with the head. This study recorded direct pressure within the brains of male Sprague-Dawley rats during exposure to blast. The goal was to understand pressure wave dynamics through the brain. In addition, we optimized in vivo methods to ensure accurate measurement of intracranial pressure (ICP). Our results demonstrate that proper sealing techniques lead to a significant increase in ICP values, compared to the outside overpressure generated by the blast. Further, the values seem to have a direct relation to a rats size and age: heavier, older rats had the highest ICP readings. These findings suggest that a global flexure of the skull by the transient shockwave is an important mechanism of pressure transmission inside the brain.

Skull Flexure as a Contributing Factor in the Mechanism of Injury in the Rat when Exposed to a Shock Wave

The manner in which energy from an explosion is transmitted into the brain is currently a highly debated topic within the blast injury community. This study was conducted to investigate the injury biomechanics causing blast-related neurotrauma in the rat. Biomechanical responses of the rat head under shock wave loading were measured using strain gauges on the skull surface and a fiber optic pressure sensor placed within the cortex. MicroCT imaging techniques were applied to quantify skull bone thickness. The strain gauge results indicated that the response of the rat skull is dependent on the intensity of the incident shock wave; greater intensity shock waves cause greater deflections of the skull. The intracranial pressure (ICP) sensors indicated that the peak pressure developed within the brain was greater than the peak side-on external pressure and correlated with surface strain. The bone plates between the lambda, bregma, and midline sutures are probable regions for the greatest flexure to occur. The data provides evidence that skull flexure is a likely candidate for the development of ICP gradients within the rat brain. This dependency of transmitted stress on particular skull dynamics for a given species should be considered by those investigating blast-related neurotrauma using animal models.

Development of biomechanical response corridors of the thorax to blunt ballistic impacts.

Human responses are critical to understanding injury biomechanics in blunt ballistic impacts, which are defined as 20-200 g projectiles impacting at 20-250 m/s. 13 human cadavers were exposed to three distinct ballistic impacts of the chest to determine force-time, deflection-time and force-deflection responses. Comparisons were made between biomechanical responses for ballistic impacts and those previously reported for lower speed, higher mass impacts. Impact condition B (140 g at 40 m/s) gave the largest peak force 10,602+/-2226 N and deflection 54.7+/-14.6 mm. Impact condition A (140 g at 20 m/s) involved lower impact energy and produced lower peak force 3383+/-761 N and deflection 25.9+/-3.1 mm, as did impact condition C (40 g at 60 m/s), which gave 3158+/-309 N and 20.1+/-7.8 mm. The results indicate each impact condition gives distinctive responses, which differ from those previously reported in the automotive literature for lower speed impacts. This information provides the foundation for future biomechanical research in the area of blunt ballistic impacts, specifically the development of test surrogates and evaluation of protective equipment.

Muscle responses to simulated torque reactions of hand-held power tools

The aim of this work was to investigate physiological responses to torque reaction forces produced by hand-held power tools used to tighten threaded fasteners. Such tools are used repetitively by workers in many industries and are often associated with upper limb musculoskeletal complaints. The tools considered for stimulation in this study had straight handles and required from 100 to 400 ms to tighten fasteners to a peak torque of 1.0 to 2.5 Nm and from 50 to 150 ms for the torque to decay to zero. A tool stimulator was constructed to apply a programmed torque profile to a handle similar to that of a straight in-line power screwdriver. Wrist flexor and extensor surface EMGs and handle position were recorded as subjects held handles subjected to controlled torque loads that tended to flex the wrist. It was found that: (1) very high EMG values occurred even though torques were of short duration (50 to 600 ms) and the peak torques were low (7-28% of maximum strength); (2) high EMGs in anticipation of torque are directly related to torque build-up rate and peak torque; (3) high peak flexor and extensor EMGs during and following torque onset are related to torque build-up rate and peak torque; (4) minimum time of peak EMGs of 72-87 ms following the onset of torques with 50 ms build-up suggests the contribution of an extensor muscle stretch reflex component; delayed peak for longer build-ups suggests a central control of muscle force in response to torque; (5) angular excursions of handles increase with decreasing torque build-up time and increasing torque magnitude causes increasing eccentric work; (6) the results show that the slow torque build-up times (450 ms) correspond to minimum peak EMGs; and (7) accumulated EMGs increase with increasing torque and torque build-up times. Further studies are needed to evaluate fatigue and musculoskeletal injuries associated with prolonged periods of tool use.

An evaluation of the cumulative concussive effect of soccer heading in the youth population

Soccer is the most popular team sport in the world, with 120 million individuals participating and 16 million of these individuals being based in the United States. In addition, soccer has become the fastest growing team sport in the United States over the past 10 years. Head impact injuries have been cited as comprising 15% of all injuries related to soccer. Previous studies have identified the technique of heading as being a significant factor in head impact injuries. In fact, 85% of various subgroups of participants, 19 years of age and older, have had a diminution in cognitive function abilities on a permanent basis. It was the purpose of this study to evaluate the effect of repetitive head impacts due to heading in 57 youth soccer players with a mean age of 11.5 years. The data were collected over three seasons during the first year, which correlated to approximately 60 games and/or practices. One team of 18 boys was followed for an additional year. The data collected included a cognitive function test, as well as documentation of concussive symptoms. These cognitive evaluations, conducted at both periods of time, revealed that statistically significant differences were not evident when compared to standardized norms with the exception of verbal learning. There was an inverse relationship between the number of ball impacts and verbal learning. Of note, however, is that 49% of the year-one study group did complain of headaches after heading the ball.

Blast-induced neurotrauma leads to neurochemical changes and neuronal degeneration in the rat hippocampus.

Blast‐induced neurotrauma is a major concern because of the complex expression of neuropsychiatric disorders after exposure. Disruptions in neuronal function, proximal in time to blast exposure, may eventually contribute to the late emergence of clinical deficits. Using magic angle spinning 1H MRS and a rodent model of blast‐induced neurotrauma, we found acute (24–48 h) decreases in succinate, glutathione, glutamate, phosphorylethanolamine and γ‐aminobutyric acid, no change in N‐acetylaspartate and increased glycerophosphorylcholine, alterations consistent with mitochondrial distress, altered neurochemical transmission and increased membrane turnover. Increased levels of the apoptotic markers Bax and caspase‐3 suggested active cell death, consistent with increased FluoroJade B staining in the hippocampus. Elevated levels of glial fibrillary acidic protein suggested ongoing inflammation without diffuse axonal injury measured by no change in β‐amyloid precursor protein. In conclusion, blast‐induced neurotrauma induces a metabolic cascade associated with neuronal loss in the hippocampus in the acute period following exposure. Copyright