Effectiveness of bicycle helmets in preventing head injury in children: case-control study.

OBJECTIVE--To examine the risk of injury to the head and the effect of wearing helmets in bicycle accidents among children. DESIGN--Case-control study by questionnaire completed by the children and their carers. SETTING--Two large children''s hospitals in Brisbane, Australia. SUBJECT--445 children presenting with bicycle related injuries during 15 April 1991 to 30 June 1992. The cases comprised 102 children who had sustained injury to the upper head including the skull, forehead and scalp or loss of consciousness. The controls were 278 cyclists presenting with injuries other than to the head or face. A further 65 children with injuries to the face were considered as an extra comparison group. MAIN OUTCOME MEASURES--Cause and type of injury, wearing of helmet. RESULTS--Most children (230) were injured after losing control and falling from their bicycle. Only 31 had contact with another moving vehicle. Children with head injury were significantly more likely to have made contact with a moving vehicle than control children (19 (19%) v 12 (4%), P < 0.001). Head injuries were more likely to occur on paved surfaces than on grass, gravel, or dirt. Wearing a helmet reduced the risk of head injury by 63% (95% confidence interval 34% to 80%) and of loss of consciousness by 86% (62% to 95%). CONCLUSIONS--The risk of head injury in bicycle accidents is reduced among children wearing a helmet. Current helmet design maximises protection in the type of accident most commonly occurring in this study. Legislation enforcing helmet use among children should be considered.     

The influence of impact force redistribution and redirection on maximum principal strain for helmeted head impacts

Abstract

Sporting helmets with linear attenuating strategies are proficient at reducing the risk of traumatic brain injury. However, the continued high incidence of concussion in American football, has led researchers to investigate novel helmet liner strategies. These strategies typically supplement existing technologies by adding or integrating head-helmet decoupling mechanisms. Decoupling strategies aim to redirect or redistribute impact force around the head, reducing impact energy transferred to the brain. This results in decreased brain tissue strain, which is beneficial in injury risk reduction due to the link between tissue strain and concussive injury.

The purpose of this study was to mathematically demonstrate the effect of ten cases, representing theoretical redirection and redistribution helmet liner strategies, on brain tissue strain resulting from impacts to the head. The kinematic response data from twenty head impacts collected in the laboratory was mathematically modified to represent the altered response of the ten different cases and used as input parameters to determine the effect on maximum principal strain (MPS) values, calculated using finite element modeling. The results showed that a reduced dominant coordinate component (contributes the greatest to resultant) of rotational acceleration decreased maximum principal strain in American football helmets. The study theoretically demonstrates that liner strategies, if applied correctly, can influence brain motion, reduce brain tissue strain, and could decrease injury risk in an American football helmet.     

Finite element modelling of equestrian helmet impacts exposes the need to address rotational kinematics in future helmet designs

Jockey head injuries, especially concussions, are common in horse racing. Current helmets do help to reduce the severity and incidences of head injury, but the high concussion incidence rates suggest that there may be scope to improve the performance of equestrian helmets. Finite element simulations in ABAQUS/Explicit were used to model a realistic helmet model during standard helmeted rigid headform impacts and helmeted head model University College Dublin Brain Trauma Model (UCDBTM) impacts.

Current helmet standards for impact determine helmet performance based solely on linear acceleration. Brain injury-related values (stress and strain) from the UCDBTM showed that a performance improvement based on linear acceleration does not imply the same improvement in head injury-related brain tissue loads. It is recommended that angular kinematics be considered in future equestrian helmet standards, as angular acceleration was seen to correlate with stress and strain in the brain.     

Injury patterns in cyclists attending an accident and emergency department: a comparison of helmet wearers and non-wearers.

OBJECTIVES--To study circumstances of bicycle accidents and nature of injuries sustained and to determine effect of safety helmets on pattern of injuries. DESIGN--Prospective study of patients with cycle related injuries. SETTING--Accident and emergency department of teaching hospital. SUBJECTS--1040 patients with complete data presenting to the department in one year with cycle related injuries, of whom 114 had worn cycle helmets when accident occurred. MAIN OUTCOME MEASURES--Type of accident and nature and distribution of injuries among patients with and without safety helmets. RESULTS--There were no significant differences between the two groups with respect to type of accident or nature and distribution of injuries other than those to the head. Head injury was sustained by 4/114 (4%) of helmet wearers compared with 100/928 (11%) of non-wearers (P = 0.023). Significantly more children wore helmets (50/309 (16%)) than did adults (64/731 (9%)) (P < 0.001). The incidence of head injuries sustained in accidents involving motor vehicles (52/288 (18%)) was significantly higher than in those not involving motor vehicles (52/754 (7%)) (chi 2 = 28.9, P < 0.0001). Multiple logistic regression analysis of probability of sustaining a head injury showed that only two variables were significant: helmet use and involvement of a motor vehicle. Mutually adjusted odds ratios showed a risk factor of 2.95 (95% confidence interval 1.95 to 4.47, P < 0.0001) for accidents involving a motor vehicle and a protective factor of 3.25 (1.17 to 9.06, P = 0.024) for wearing a helmet. CONCLUSION--The findings suggest an increased risk of sustaining head injury in a bicycle accident when a motor vehicle is involved and confirm protective effect of helmet wearing for any bicycle accident.     

Differences in outcomes of mandatory motorcycle helmet legislation by country income level: A systematic review and meta-analysis

BackgroundThe recent Lancet Commission on Legal Determinants of Global Health argues that governance can provide the framework for achieving sustainable development goals. Even though over 90% of fatal road traffic injuries occur in low- and middle-income countries (LMICs) primarily affecting motorcyclists, the utility of helmet laws outside of high-income settings has not been well characterized. We sought to evaluate the differences in outcomes of mandatory motorcycle helmet legislation and determine whether these varied across country income levels.Methods and findingsA systematic review and meta-analysis were completed using the PRISMA checklist. A search for relevant articles was conducted using the PubMed, Embase, and Web of Science databases from January 1, 1990 to August 8, 2021. Studies were included if they evaluated helmet usage, mortality from motorcycle crash, or traumatic brain injury (TBI) incidence, with and without enactment of a mandatory helmet law as the intervention. The Newcastle–Ottawa Scale (NOS) was used to rate study quality and funnel plots, and Begg’s and Egger’s tests were used to assess for small study bias. Pooled odds ratios (ORs) and their 95% confidence intervals (CIs) were stratified by high-income countries (HICs) versus LMICs using the random-effects model. Twenty-five articles were included in the final analysis encompassing a total study population of 31,949,418 people. There were 17 retrospective cohort studies, 2 prospective cohort studies, 1 case–control study, and 5 pre–post design studies. There were 16 studies from HICs and 9 from LMICs. The median NOS score was 6 with a range of 4 to 9. All studies demonstrated higher odds of helmet usage after implementation of helmet law; however, the results were statistically significantly greater in HICs (OR: 53.5; 95% CI: 28.4; 100.7) than in LMICs (OR: 4.82; 95% CI: 3.58; 6.49), p-value comparing both strata < 0.0001. There were significantly lower odds of motorcycle fatalities after enactment of helmet legislation (OR: 0.71; 95% CI: 0.61; 0.83) with no significant difference by income classification, p-value: 0.27. Odds of TBI were statistically significantly lower in HICs (OR: 0.61, 95% CI 0.54 to 0.69) than in LMICs (0.79, 95% CI 0.72 to 0.86) after enactment of law (p-value: 0.0001). Limitations of this study include variability in the methodologies and data sources in the studies included in the meta-analysis as well as the lack of available literature from the lowest income countries or from the African WHO region, in which helmet laws are least commonly present.ConclusionsIn this study, we observed that mandatory helmet laws had substantial public health benefits in all income contexts, but some outcomes were diminished in LMIC settings where additional measures such as public education and law enforcement might play critical roles.

In a systematic review and meta-analysis, Jacob Lepard and colleagues evaluate the differences in outcomes of mandatory motorcycle helmet legislation by country-income level.     

Towards reducing impact-induced brain injury: lessons from a computational study of army and football helmet pads

We use computational simulations to compare the impact response of different football and U.S. Army helmet pad materials. We conduct experiments to characterise the material response of different helmet pads. We simulate experimental helmet impact tests performed by the U.S. Army to validate our methods. We then simulate a cylindrical impactor striking different pads. The acceleration history of the impactor is used to calculate the head injury criterion for each pad. We conduct sensitivity studies exploring the effects of pad composition, geometry and material stiffness. We find that (1) the football pad materials do not outperform the currently used military pad material in militarily relevant impact scenarios; (2) optimal material properties for a pad depend on impact energy and (3) thicker pads perform better at all velocities. Although we considered only the isolated response of pad materials, not entire helmet systems, our analysis suggests that by using larger helmet shells with correspondingly thicker pads, impact-induced traumatic brain injury may be reduced.     

The influence of impact source on variables associated with strain for impacts in ice hockey

Concussion can occur from a variety of events (falls to ice, collisions etc) in ice hockey, and as a result it is important to identify how these different impact sources affect the relationship between impact kinematics and strain that has been found to be associated to this injury. The purpose of this research was to examine the relationship between kinematic variables and strain in the brain for impact sources that led to concussion in ice hockey. Video of professional ice hockey games was analyzed for impacts that resulted in reported clinically diagnosed concussions. The impacts were reconstructed using physical models/ATDs to determine the impact kinematics and then simulated using finite element modelling to determine maximum principal strain and cumulative strain damage measure. A stepwise linear regression was conducted between linear acceleration, change in linear velocity, rotational acceleration, rotational velocity, and strain response in the brain. The results for the entire dataset was that rotational acceleration had the highest r² value for MPS (r² = 0.581) and change in rotational velocity for cumulative strain damage measure (r² = 450). When the impact source (shoulder, elbow, boards, or ice impacts) was isolated the rotational velocity and acceleration r² value increased, indicating that when evaluating the relationships between kinematics and strain based metrics the characteristics of the impact is an important factor. These results suggest that rotational measures should be included in future standard methods and helmet innovation and design in ice hockey as they have the highest association with strain in the brain tissues.     

Dosimetric impact of uncorrected systematic yaw rotation in VMAT for peripheral lung SABR

AimThis study aimed to evaluate the dosimetric impact of uncorrected yaw rotational error on both target coverage and OAR dose metrics in this patient population.BackgroundRotational set up errors can be difficult to correct in lung VMAT SABR treatments, and may lead to a change in planned dose distributions.Materials and methodsWe retrospectively applied systematic yaw rotational errors in 1° degree increments up to −5° and +5° degrees in 16 VMAT SABR plans. The impact on PTV and OARs (oesophagus, spinal canal, heart, airway, chest wall, brachial plexus, lung) was evaluated using a variety of dose metrics. Changes were assessed in relation to percentage deviation from approved planned dose at 0 degrees.ResultsTarget coverage was largely unaffected with the largest mean and maximum percentage difference being 1.4% and 6% respectively to PTV D98% at +5 degrees yaw.Impact on OARs was varied. Minimal impact was observed in oesophagus, spinal canal, chest wall or lung dose metrics. Larger variations were observed in the heart, airway and brachial plexus. The largest mean and maximum percentage differences being 20.77% and 311% respectively at −5 degrees yaw to airway D0.1cc, however, the clinical impact was negligible as these variations were observed in metrics with minimal initial doses.ConclusionsNo clinically unacceptable changes to dose metrics were observed in this patient cohort but large percentage deviations from approved dose metrics in OARs were noted. OARs with associated PRV structures appear more robust to uncorrected rotational error.     

Evaluation of helmet and goggle designs by modeling non-penetrating projectile impacts

Despite the progress in developing personal combat-protective gear, eye and brain injuries are still widely common and carry fatal or long-term repercussions. The complex nature of the cranial tissues suggests that simple methods (e.g. crash-dummies) for testing the effectiveness of personal protective gear against non-penetrating impacts are both expensive and ineffective, and there are ethical issues in using animal or cadavers. The present work presents a versatile testing framework for quantitatively evaluating protective performances of head and eye combat-protective gear, against non-penetrating impacts. The biomimetic finite element (FE) head model that was developed provides realistic representation of cranial structure and tissue properties. Simulated crash impact results were validated against a former cadaveric study and by using a crash-phantom developed in our lab. The model was then fitted with various helmet and goggle designs onto which a non-penetrating ballistic impact was applied. Example data show that reduction of the elastic and shear moduli by 30% and 80% respectively of the helmet outer Kevlar-29 layer, lowered intracranial pressures by 20%. Our modeling suggests that the level of stresses that develop in brain tissues, which ultimately cause the brain damage, cannot be predicted solely by the properties of the helmet/goggle materials. We further found that a reduced contact area between goggles and face is a key factor in reducing the mechanical loads transmitted to the optic nerve and eye balls following an impact. Overall, this work demonstrates the simplicity, flexibility and usefulness for development, evaluation, and testing of combat-protective equipment using computational modeling.

• Highlights

• A finite element head model was developed for testing head gear.

• Reduced helmet’s outer layer elastic and shear moduli lowered intracranial stresses.

• Gear material properties could not fully predict impact-related stress in the brain.

• Reduced goggles-face contact lowered transmitted loads to the optic nerve and eyes.

     

Finite element analysis for the evaluation of protective functions of helmets against ballistic impact

The ballistic impact of a human head model protected by a Personnel Armor System Ground Troops Kevlar^® helmet is analysed using the finite element method. The emphasis is to examine the effect of the interior cushioning system as a shock absorber in mitigating ballistic impact to the head. The simulations of the frontal and side impacts of the full metal jacket (FMJ) and fragment-simulating projectile (FSP) were carried out using LS-DYNA. It was found that the Kevlar^® helmet with its interior nylon and leather strap was able to defeat both the FMJ and FSP without the projectiles penetrating the helmet. However, the head injuries caused by the FMJ impact can be fatal due to the high stiffness of the interior strap. The bulge section at the side of the Kevlar^® helmet had more room for deformation that resulted in less serious head injuries.     

Simulation-based assessment for construction helmets

In recent years, there has been a concerted effort for greater job safety in all industries. Personnel protective equipment (PPE) has been developed to help mitigate the risk of injury to humans that might be exposed to hazardous situations. The human head is the most vulnerable to impact as a moderate magnitude can cause serious injury or death. That is why industries have required the use of an industrial hard hat or helmet. There have only been a few articles published to date that are focused on the risk of head injury when wearing an industrial helmet. A full understanding of the effectiveness of construction helmets on reducing injury is lacking. This paper presents a simulation-based method to determine the threshold at which a human will sustain injury when wearing a construction helmet and assesses the risk of injury for wearers of construction helmets or hard hats. Advanced finite element, or FE, models were developed to study the impact on construction helmets. The FE model consists of two parts: the helmet and the human models. The human model consists of a brain, enclosed by a skull and an outer layer of skin. The level and probability of injury to the head was determined using both the head injury criterion (HIC) and tolerance limits set by Deck and Willinger. The HIC has been widely used to assess the likelihood of head injury in vehicles. The tolerance levels proposed by Deck and Willinger are more suited for finite element models but lack wide-scale validation. Different cases of impact were studied using LSTC's LS-DYNA.     

A centric/non-centric impact protocol and finite element model methodology for the evaluation of American football helmets to evaluate risk of concussion

American football reports high incidences of head injuries, in particular, concussion. Research has described concussion as primarily a rotation dominant injury affecting the diffuse areas of brain tissue. Current standards do not measure how helmets manage rotational acceleration or how acceleration loading curves influence brain deformation from an impact and thus are missing important information in terms of how concussions occur. The purpose of this study was to investigate a proposed three-dimensional impact protocol for use in evaluating football helmets. The dynamic responses resulting from centric and non-centric impact conditions were examined to ascertain the influence they have on brain deformations in different functional regions of the brain that are linked to concussive symptoms. A centric and non-centric protocol was used to impact an American football helmet; the resulting dynamic response data was used in conjunction with a three-dimensional finite element analysis of the human brain to calculate brain tissue deformation. The direction of impact created unique loading conditions, resulting in peaks in different regions of the brain associated with concussive symptoms. The linear and rotational accelerations were not predictive of the brain deformation metrics used in this study. In conclusion, the test protocol used in this study revealed that impact conditions influences the region of loading in functional regions of brain tissue that are associated with the symptoms of concussion. The protocol also demonstrated that using brain deformation metrics may be more appropriate when evaluating risk of concussion than using dynamic response data alone.     

Brain tissue analysis of impacts to American football helmets

Concussion in American football is a prevalent concern. Research has been conducted examining frequencies, location, and thresholds for concussion from impacts. Little work has been done examining how impact location may affect risk of concussive injury. The purpose of this research was to examine how impact site on the helmet and type of impact, affects the risk of concussive injury as quantified using finite element modelling of the human head and brain. A linear impactor was used to impact a helmeted Hybrid III headform in several locations and using centric and non-centric impact vectors. The resulting dynamic response was used as input for the Wayne State Brain Injury Model to determine the risk of concussive injury by utilizing maximum principal strain as the predictive variable. The results demonstrated that impacts that occur primarily to the side of the head resulted in higher magnitudes of strain in the grey and white matter, as well as the brain stem. Finally, commonly worn American football helmets were used in this research and significant risk of injury was incurred for all impacts. These results suggest that improvements in American football helmets are warranted, in particular for impacts to the side of the helmet.     

A six degree of freedom head acceleration measurement device for use in football

The high incidence rate of concussions in football provides a unique opportunity to collect biomechanical data to characterize mild traumatic brain injury. The goal of this study was to validate a six degree of freedom (6DOF) measurement device with 12 single-axis accelerometers that uses a novel algorithm to compute linear and angular head accelerations for each axis of the head. The 6DOF device can be integrated into existing football helmets and is capable of wireless data transmission. A football helmet equipped with the 6DOF device was fitted to a Hybrid III head instrumented with a 9 accelerometer array. The helmet was impacted using a pneumatic linear impactor. Hybrid III head accelerations were compared with that of the 6DOF device. For all impacts, peak Hybrid III head accelerations ranged from 24 g to 176 g and 1,506 rad/s(2) to 14,431 rad/s(2). Average errors for peak linear and angular head acceleration were 1% ± 18% and 3% ± 24%, respectively. The average RMS error of the temporal response for each impact was 12.5 g and 907 rad/s(2).     

Nonuse of bicycle helmets and risk of fatal head injury: a proportional mortality, case�Ccontrol study

Background:

The effectiveness of helmets at preventing cycling fatalities, a leading cause of death among young adults worldwide, is controversial, and safety regulations for cycling vary by jurisdiction. We sought to determine whether nonuse of helmets is associated with an increased risk of fatal head injury.

Methods:

We used a case–control design involving 129 fatalities using data from a coroner’s review of cycling deaths in Ontario, Canada, between 2006 and 2010. We defined cases as cyclists who died as a result of head injuries; we defined controls as cyclists who died as a result of other injuries. The exposure variable was nonuse of a bicycle helmet.

Results:

Not wearing a helmet while cycling was associated with an increased risk of dying as a result of sustaining a head injury (adjusted odds ratio [OR] 3.1, 95% confidence interval [CI] 1.3–7.3). We saw the same relationship when we excluded people younger than 18 years from the analysis (adjusted OR 3.5, 95% CI 1.4–8.5) and when we used a more stringent case definition (i.e., only a head injury with no other substantial injuries; adjusted OR 3.6, 95% CI 1.2–10.2).

Interpretation:

Not wearing a helmet while cycling is associated with an increased risk of sustaining a fatal head injury. Policy changes and educational programs that increase the use of helmets while cycling may prevent deaths.One cyclist dies in Canada each week, and cycling fatalities account for more than 2% of traffic fatalities, a leading cause of death in young adults.¹ Cycling safety regulations vary by jurisdiction, and controversy remains about the effectiveness of safety measures such as helmets. There is strong evidence that helmets prevent nonfatal head injuries,² but very limited evidence exists related to fatal head injuries. A meta-analysis of case–control studies showed a protective effect of helmets against head injuries, but it was based on just 4 case fatalities in which helmets were not worn.³ Another large study involving 1710 cycling collisions found a trend toward a protective effect of helmets, but included only 14 fatalities.⁴ The existing literature leaves open the possibility that helmets prevent nonfatal head injuries, but not fatal ones.We sought to determine whether cycling without a helmet was associated with an increased risk of sustaining a fatal head injury.     

Evaluation of a flexible force sensor for measurement of helmet foam impact performance

The association between translational head acceleration and concussion remains unclear and provides a weak predictive measure for this type of injury; thus, alternative methods of helmet evaluation are warranted. Recent finite element analysis studies suggest that better estimates of concussion risk can be obtained when regional parameters of the cranium, brain and surrounding tissues are included. Lacking, however, are empirical data at the head–helmet interface with regards to contact area and force. Hence, the purpose of this study was to evaluate a system to capture the impact force distribution of helmet foams. Thirteen Flexiforce^® sensors were arranged in a 5×5 cm array, secured to a load cell. Three densities of foam were repeatedly impacted with 5 J of energy during ambient (20 °C) and cold (?25 °C) conditions. RMS error, calculated relative to the global force registered by the load cell, was <1.5% of the measurement range during individual calibration of the Flexiforce^® sensors. RMS error was 5% of the measured range for the global force estimated by the sensor array. Load distribution measurement revealed significant differences between repeated impacts of cold temperature foams for which acceleration results were non-significant. The sensor array, covering only 36% of the total area, possessed sufficient spatial and temporal resolution to capture dynamic load distribution patterns. Implementation of this force mapping system is not limited to helmet testing. Indeed it may be adopted to assess other body regions vulnerable to contact injuries (e.g., chest, hip and shin protectors).     

Efficacy of two intervention approaches on functional walking capacity and balance in children with Duchene muscular dystrophy

Objectives:Children with Duchene muscular dystrophy have weak muscles, which may impair postural adjustments. These postural adjustments are required for gait and dynamic balance during the daily living activities. The aim was to compare between the effect of bicycle ergometer versus treadmill on functional walking capacity and balance in children with Duchenne muscular dystrophy.Methods:Thirty boys aged from 6 to 10 years old diagnosed as Duchene muscular dystrophy participated in this study. Children were assigned randomly into two groups (A&B). Children in group (A) underwent a designed program of physical therapy plus aerobic exercise training in form of bicycle ergometer while, group (B) received the same program as group (A) and aerobic exercise training by treadmill for one hour, at three times a week for three successive months. Functional walking capacity and balance were assessed before and after treatment by using the 6-minute walk test and Biodex balance system equipment respectively.Results:The post treatment results revealed significant difference in all measured variables (P<0.05) as compared with its pre-treatment results. Post-treatment values indicated that there was a significant difference in all measured variables in favor of group B.Conclusions:treadmill training as an aerobic exercise can improve walking capacity and balance more effectively than bicycle ergometer in children with Duchenne muscular dystrophy.     

The effects of joint hypermobility syndrome on the kinematics and kinetics of the vertical jump test

PurposeBiomechanical impairments are not apparent during walking in people with Joint Hypermobility Syndrome (JHS). This research explored biomechanical alterations during a higher intensity task, vertical jumping.Materials and methodsThis cross-sectional study compared a JHS group (n = 29) to a healthy control group (n = 30). Joint kinematics and kinetics were recorded using a Qualisys motion capture system synchronized with a Kistler platform. Independent sample t-tests and standardised mean differences (SMD) were used for statistical analysis.ResultsNo significant statistical or clinical differences were found between groups in joint kinematics and jump height (p ≥ 0.01). Sagittal hip and knee peak power generation were statistically lower in the JHS group during the compression phase (p ≤ 0.01), but not clinically relevant (SMD < 0.5). Clinically relevant reductions were found in the JHS group knee and ankle peak moments during the compression phase, and hip and knee peak power generation during the push phase (SMD ≥ 0.5), although these were not statistically significant (p ≥ 0.01).ConclusionThe JHS group achieved a similar jump height but with some biomechanical alterations. Further understanding of the joint biomechanical behavior could help to optimize management strategies for JHS, potentially focusing on neuromuscular control and strength/power training.     

Maximizing and evaluating the impact of test-trace-isolate programs: A modeling study

BackgroundTest-trace-isolate programs are an essential part of coronavirus disease 2019 (COVID-19) control that offer a more targeted approach than many other nonpharmaceutical interventions. Effective use of such programs requires methods to estimate their current and anticipated impact.Methods and findingsWe present a mathematical modeling framework to evaluate the expected reductions in the reproductive number, R, from test-trace-isolate programs. This framework is implemented in a publicly available R package and an online application. We evaluated the effects of completeness in case detection and contact tracing and speed of isolation and quarantine using parameters consistent with COVID-19 transmission (R₀: 2.5, generation time: 6.5 days). We show that R is most sensitive to changes in the proportion of cases detected in almost all scenarios, and other metrics have a reduced impact when case detection levels are low (<30%). Although test-trace-isolate programs can contribute substantially to reducing R, exceptional performance across all metrics is needed to bring R below one through test-trace-isolate alone, highlighting the need for comprehensive control strategies. Results from this model also indicate that metrics used to evaluate performance of test-trace-isolate, such as the proportion of identified infections among traced contacts, may be misleading. While estimates of the impact of test-trace-isolate are sensitive to assumptions about COVID-19 natural history and adherence to isolation and quarantine, our qualitative findings are robust across numerous sensitivity analyses.ConclusionsEffective test-trace-isolate programs first need to be strong in the “test” component, as case detection underlies all other program activities. Even moderately effective test-trace-isolate programs are an important tool for controlling the COVID-19 pandemic and can alleviate the need for more restrictive social distancing measures.     

On the accuracy of the Head Impact Telemetry (HIT) System used in football helmets

On-field measurement of head impacts has relied on the Head Impact Telemetry (HIT) System, which uses helmet mounted accelerometers to determine linear and angular head accelerations. HIT is used in youth and collegiate football to assess the frequency and severity of helmet impacts. This paper evaluates the accuracy of HIT for individual head impacts. Most HIT validations used a medium helmet on a Hybrid III head. However, the appropriate helmet is large based on the Hybrid III head circumference (58 cm) and manufacturer's fitting instructions. An instrumented skull cap was used to measure the pressure between the head of football players (n=63) and their helmet. The average pressure with a large helmet on the Hybrid III was comparable to the average pressure from helmets used by players. A medium helmet on the Hybrid III produced average pressures greater than the 99th percentile volunteer pressure level. Linear impactor tests were conducted using a large and medium helmet on the Hybrid III. Testing was conducted by two independent laboratories. HIT data were compared to data from the Hybrid III equipped with a 3-2-2-2 accelerometer array. The absolute and root mean square error (RMSE) for HIT were computed for each impact (n=90). Fifty-five percent (n=49) had an absolute error greater than 15% while the RMSE was 59.1% for peak linear acceleration.