Designing flocked energy-absorbing material layers into sport and military helmet pads

A systematic study is reported on applying flocked energy-absorbing materials (FEAM) to designing sport and military helmet pad structures. An executed parametric study shows that the impact force absorbing (IFA) properties of FEAM elements are optimized when using (a) higher denier flock fiber (60 to 100 denier) and (b) longer flock fibers (3 to 4 mm length) at higher flock densities. Continuing work focuses on the importance of IFA/areal density ratios in helmet pad functional design. It is found that foam materials like vinyl-nitrile and ethylene vinyl acetate (EVA) inherently exhibit higher IFA/areal density (IFA/AD) ratios than FEAM material structures. With this finding, a new strategy for developing sport and military helmet pads was devised involving the combination of foam and FEAM layer elements. Here, the meritorious properties of foam materials (light weight and excellent IFA properties) and the excellent IFA and breathability (wearer comfort, sweat and heat management) properties of FEAM could be favorably encompassed. A plan was conceived and implemented whereby combination foam/FEAM test pads having high amounts of the high IFA/AD ratio VN-600 or EVA foam layer component were impact tested. By gradually introducing the more comfortable, breathable, body-heat managing FEAM layers into the helmet pad structure, some “trade-off” helmet pad configurations were designed and evaluated. Experiments showed that helmet pad designs having not more than 40% to 50% FEAM content should produce adequate IFA/AD ratio “trade-off” property helmet pad configurations.

Upright Magnetic Resonance Imaging Study of Cervical Flexor/Extensor Musculature and Cervical Lordosis in Females After Helmet Wear

ABSTRACT Introduction Addition of head-supported mass imparts greater demand on the human neck to maintain functionality. The same head-supported mass induces greater demand on the female spine than the male spine because female necks are comparatively slender. Prevalence of neck pain is greater in military than civilian population because of the head-borne mass (among other factors). The goal of this study is to determine quantifiable parameters related to muscle geometry using female human volunteers and upright magnetic resonance imaging. Materials and Methods Young healthy subjects were consented. Demographics and head–neck anthropometry were recorded. For all the 7 subjects, the T1- and T2-weighted magnetic resonance imaging in the neutral sitting position was obtained immediately following donning and after 4 hours of continuous wear of standard issued military helmet, while seated in the same posture for 4 hours. Cross-sectional areas of sternocleidomastoid and multifidus muscles from C2-C7, overall and segmental Cobb angles (C2-T1), and centroid and radius of each muscle were calculated. Data were compared with determine differences with the continuous helmet wear. Results There were level specific changes in morphological parameters for each of the muscles. Significant difference (P < 0.05) in cross-sectional areas was noted at C2-3 level for sternocleidomastoid and at C3-4 and C5-6 levels for multifidus. For centroid angles, significant difference (P < 0.05) was observed at C2-3 and C5-6 levels for sternocleidomastoid and at C3-4 level for multifidus. There was no significant difference (P > 0.05) in muscle centroid radii between the pre- and posttest conditions. Conclusions Alterations in muscle geometries were muscle specific and level specific: sternocleidomastoid was significant at the upper level, whereas multifidus was significant at the mid-lower cervical spine segments. The insignificant difference in the Cobb angles was attributed to length of time of continuous helmet wear attributed and sample size. Helmet wear can lead to morphometric alterations in cervical flexor/extensor musculature in females.

407 Is Pickelhaube Sign really the hallmark of arrhythmogenic MVP in athletes? And does MVP really cause sudden death? A case report

The Pickelhaube Sign is today recognized as a novel Echocardiographic Risk Marker for Malignant Mitral Valve Prolapse Syndrome. Mitral Valve Prolapse (MVP) has long been recognized to be a relatively common valve abnormality in the general population. Patients with relatively non-specific symptoms and asymptomatic athletes who have MVP still represent an important clinical conundrum for any physician involved in preventive medicine and sports screening. Although cardiac arrhythmias and/or cardiac death are an undesirable problem in MVP patients, when these subjects were studied with Holter Electrocardiogram (ECG) monitoring a prevalence of ventricular arrhythmias up to 34% was observed, with premature ventricular contractions as the most common pattern (66% of cases). At this regard a paper by Anders et al. described a series of cases that suggest that even clinically considered benign cases of MVP in young adults may cause sudden and unexpected death. However, cardiac arrest and Sudden Arrhythmic Cardiac Death (SCD) resulted in rare events only in patients with MVP based on data from a community study. A middle-aged athletic male who has been practicing competitive cycling for about 20 years came to our Sports Medicine Centre to undergo screening of sports preparation for competitive cycling and the related renewal of certification for participation in sports competitions. This athlete was always considered suitable in previous competitive fitness assessments performed in other sports medicine centers. His family history was unremarkable, as well as his recent and remote pathological anamnesis. The physical examination revealed a 3/6 regurgitation heart murmur with a click in the mid late systole. Previous echocardiographic examinations revealed a MVP which was considered benign with mild not relevant mitral regurgitation. He did not complain of symptoms such as dyspnoea or heart palpitations during physical activity. The resting ECG showed negative T waves in the inferior limb leads, and the stress test showed sporadic premature ventricular beats (a couple) with right bundle branch block morphology. An echocardiogram confirmed the presence of a classic mitral valve prolapse with billowing of both mitral leaflets, associated with a mild to moderate valve regurgitation. The TDI exam at the level of the lateral mitral annulus showed a high-velocity mid-systolic spike like a Pickelhaube sign, i.e. spiked German military helmet morphology. Consequently, an in-depth diagnostic imaging with cardiac magnetic resonance imaging was proposed, but the athlete refused it, both because he was totally asymptomatic and above all because he would be forced to pay a considerable amount of money as the examination is not guaranteed by the Italian National Health Service. In conclusion, the athlete remained sub judice as for competitive suitability, Finally, the question is: does MVP really cause sudden death? Is it enough to detect the Pickelhaube signal by echocardiography to stop this athlete? Let us bear in mind that this athlete was asymptomatic, and he had not had any trouble during exercise and maximal effort for many years. Why must we declare him unsuitable to do competitive sports?

Rate Dependent Material Model for Helmet Pads

Foam pads are commonly used in sports and military helmet for energy absorption, form-fitting and comfort. Both for low velocity and high velocity applications, their rate-dependent mechanical properties need to be characterized to understand their ability to effectively modulate the transmitted stress pulse. Impact experiments were conducted on bilayer helmet pads at a range of velocities covering low to medium rates up to ∼7000/s. Images from high-speed camera were used to construct x-T diagrams to measure the shock speeds from the impact experiments. Numerical simulations were carried out to validate a foam pad model and to understand experimental uncertainties. The scatter in the measured shock speeds was found to be related to the scatter in the material properties.

UK military helmet design and test methods

The aim of this paper was to provide the military medical community with an expert summary of military helmets used by HM Armed Forces. The design of military helmets and test methods used to determine the fragmentation and non-ballistic impact protection are discussed. The helmets considered are Parachutist, Combat Vehicle Crewman, Mk6, Mk6A, Mk7 and VIRTUS. The helmets considered provide different levels of fragmentation and non-ballistic impact protection dictated by the materials available at the time of the helmet design and the end-user requirement. The UK Ministry of Defence defines the area of coverage of military helmets by considering external anatomical features to provide protection to the brain and the majority of the brainstem. Established test methods exist to assess the performance of the helmet with respect to the threats; however, these test methods do not typically consider anatomical vulnerability.

Helmet-induced headache among Danish military personnel

Aims: External compression headache is defined as a headache caused by an external physical compression applied on the head. It affects about 4% of the general population; however, certain populations (e.g. construction workers and military personnel) with particular needs of headwear or helmet are at higher risk of developing this type of headache. External compression headache is poorly studied in relation to specific populations. This study aimed to investigate the prevalence and pattern of helmet-induced external compression headache among Danish military personnel of the Northern Jutland region in Denmark. Methods: Data acquisition was based on a custom-made questionnaire delivered to volunteers who used helmets in the Danish military service and who agreed to participate in this study. The military of the Northern Jutland region of Denmark facilitated recruitment of the participants. The questionnaires were delivered on paper and the collected (anonymous) answers (total 279) were used for further analysis. Results: About 30% of the study participants reported headache in relation to wearing a military helmet. Headache was defined as a pressing pain predominantly in the front of the head with an average intensity of 4 on a visual analogue scale of 0 (no pain) to 10 (worst pain imaginable). It was also found that helmets with different designs influenced both the occurrence of headache and its characteristics. Conclusions: This study is the first to demonstrate the prevalence and pattern of compression headache among military personnel in North Jutland, Denmark. The findings of this study call for further attention to helmet-induced external compression headache and strategies to minimize the burden.