INTRODUCTION:Cervical spine musculature contributes to stability and load carrying capacity of the human head-neck. As muscle morphologies influence segmental neck biomechanics and physiological responses to operational activities, their accurate description in computational musculoskeletal models is needed to better estimate osteoligamentous column loads, and determine the mechanisms of internal load transfer, and segmental and local component load sharing. Cervical muscle morphologies specific to fighter jet pilot populations have not been included in the current musculoskeletal injury models. The objective of the current preliminary descriptive study was to obtain muscle morphological data from a group of pilots from the US Air Force. MATERIALS AND METHODS:Supine magnetic resonance images (MRIs) were taken from nine experienced pilot subjects. Cross-sectional areas of the flexor (longus capitis, longus colli, and sternocleidomastoid) and extensor (semispinalis and spinalis cervicis, semispinalis capitis, and multifidus) muscles of the sub-axial spine were obtained. Muscles were segmented on the axial view images at the inferior vertebral endplate (the inferior axial section of the vertebral body) for each spinal segment. RESULTS:The mean age, stature, total body mass, and body mass index of two female and seven male pilots were 39 ± 5 years, 1.8 ± 0.1 m, 83 ± 8 kg, and 27 ± 2 kg/m2, respectively. These data for the females were 3 ± 5 years, 1.7 ± 0.01 m, 75 ± 4 kg, and 27 ± 1 kg/m2, and for the males were 41 ± 5 years, 1.8 ± 0.1 m, 85 ± 8 kg, and 26 ± 2 kg/m2, respectively. In the flexor group, the area of the sternocleidomastoid muscle decreased cranially from the lower cervical spine (C5 and C6 levels), although the longus colli muscle did not demonstrate such tendency. The longus capitis muscle increased from the lower (C5-C7) to the upper cervical levels, with a peak at the C3. In the extensor group, the area of the semispinalis capitis increased from the inferior to the superior direction although the spinalis cervicis muscles areas showed an inverse pattern. In contrast, the areas of the semispinalis cervicis and multifidus muscles did not show a pattern from the upper to lower or from the lower to upper cervical levels. Level specific data are given in the body of the main paper. CONCLUSIONS:The areas obtained from MRIs at different levels of the cervical column from a group of military pilots showed that their variations depend on muscle type and action. As fighter pilots were the subjects, the primary finding about the patterns in the muscle cross-sectional areas is related to the use of head supported mass, cockpit ergonomics, posture, head accelerations from high-g forces that the pilot experiences, and other factors. From this perspective, the present results are unique. Although the study had more males, an evenly matched group is necessary to elicit male-female differences. It would be a future study to enroll more female fighter pilots to delineate males-to-female differences. The current data can be used in musculoskeletal models to predict realistic neck loads, internal stresses and strains, and anterior and posterior column load sharing under military loading scenarios.

INTRODUCTION:A 2022 survey conducted by Headquarters Air Combat Command Aircrew Performance Branch found that 98% of fighter aircrew reported flight-related neck pain during their career. Despite the high prevalence of neck pain and growing operational demands, there remains no consensus regarding best practices for mitigating aircrew pain and injury. Although most pilot training locations have established aircrew performance teams, only select locations have mandated training hours to support injury mitigation training. Eglin Air Force Base (EAFB) F-35A student pilots (SPs) engage in a mandatory 8-week standardized spine training program (STP). In contrast, the F-15E Flying Course at Seymour Johnson Air Force Base (SJAFB) does not have syllabus hours to support the STP, resulting in the capability to utilize this site as a comparison group for this analysis. The primary objective of this study was to determine if completion of the STP led to significant differences in the Cervical Endurance Hold (CEH). We hypothesized that SPs would exhibit significant training adaptations only if they had dedicated training hours that could support the completion of the STP. MATERIALS AND METHODS:SPs from EAFB who were actively enrolled in the F-35A Flying Course from 2022 to 2024 participated in an 8-week STP. The CEH test was administered before the start of the Flying Course (pre-flying training), after the 8-week STP intervention (post-8 week), after the air-to-air phase of training (post air-to-air), and after the completion of the Flying Course (post-flying training). SPs from SJAFB who were actively enrolled in the F-15E Flying Course from 2022 to 2024 did not participate in the standardized STP. The CEH test was administered before the Flying Course (pre-flying training) and following the completion of the Flying Course (post-flying training). JMP 16.0 (SAS Institute Inc., Cary, NC, United States) was used to retrospectively analyze the data from this study. RESULTS:There was a significant effect from the STP between the intervention (EAFB) and comparison (SJAFB) groups (F(1,81.28) = 7.456; P = .008). Additionally, the STP had a significantly positive effect on CEH time, following the initial 8-week intervention (pre-training = 96.28s ± (37.95s), 8-week = 132.81 seconds ± (30.96s) P < .001), which was maintained throughout the duration of the Flying Course (pre-training = 96.28s ± (37.95s), post-training = 117.34s ± (29.73s) P = .013). CONCLUSIONS:The study results show a significant improvement in CEH outcomes after the 8-week STP intervention, which was not seen at the comparison site. Notably, the benefits of the STP at the intervention site were sustained even after the Flying Course was completed, indicating that the program may have a sustained protective effect. Future analysis of flight profiles between locations that implement the STP and those that do not should be conducted. This comparison could help determine whether the STP is contributing to a reduction in duty limitations. Furthermore, if a relationship exists, these findings may provide valuable insights for experts seeking the most effective spine training methods to mitigate pain, injury, and attrition in fighter aircrew.

ObjectiveTo evaluate neck muscle coactivation across different levels of mental workload during simulated flight tasks.BackgroundNeck pain (NP) is highly prevalent among military aviators. Given the complex nature within the flight environment, mental workload may be a risk factor for NP. This may induce higher levels of neck muscle coactivity, which over time may accelerate fatigue, increase neck discomfort, and affect flight task performance.MethodThree counterbalanced mental workload conditions represented by simulated flight tasks modulated by interstimulus frequency and complexity were investigated using the Modifiable Multitasking Environment (ModME). The primary measure was a neck coactivation index to describe the neuromuscular effort of the neck muscles as a system. Additional measures included perceived workload (NASA TLX), subjective discomfort, and task performance. Participants (n = 60; 30M, 30F) performed three test conditions over 1 hr each while seated in a simulated seating environment.ResultsNeck coactivation indices (CoA) and subjective neck discomfort corresponded with increasing level of mental workload. Average CoAs for low, medium, and high workloads were: .0278(SD = .0232), .0286(SD = .0231), and .0295(SD = .0228), respectively. NASA TLX mental, temporal, effort, and overall scores also increased with the level of mental workload assigned. For ModME task performance, the overall performance score, monitoring accuracy, and resource management accuracy decreased while reaction times increased with the increasing level of mental workload. Communication accuracy was lowest with the low mental workload but had higher reaction times relative to increasing workload.ConclusionMental workload affects neck muscle coactivation during combinations of simulated flight tasks within a simulated helicopter seating environment.ApplicationThe results of this study provide insights into the physical response to mental workload. With increasing multisensory modalities within the work environment, these insights may assist the consideration of physical effects from cognitive factors.

Background: Motion Sickness increases risk of performance deficits and safety of flight concerns. The etiology of motion sickness is poorly understood. Here, we attempted to quantify the physiological effects of motion sickness on static balance and determine the genetic predictors associated with these effects. Methods: 16 subjects underwent a disorientation stimulus to induce motion sickness. Motion sickness susceptibility was identified using the Motion Sickness Susceptibility Questionnaire. Postural balance outcomes were measured using two tasks, and small ribonucleic acid profiles were assessed with blood draws before motion sickness stimulus. Differences in postural sway before and after the stimulus as well as effect modification of susceptibility were assessed. A random forest followed by regression tree analysis was constructed for each postural sway variable to determine top genetic and covariate predictors. Findings: Significant differences existed in mean postural balance responses between before and after stimulus. Individuals with longer stimulus survival experienced a greater (but insignificant) perception of sway, even if not displaying increased sway for all conditions. Circulation small ribonucleic acids were differentially expressed between individuals with long and short stimulus survival, many of these microRNA have purported targets in genes related to vestibular disorders. Interpretation: We found motion sickness produces transient motor dysfunction in a healthy military population. Small ribonucleic acids were differentially expressed between subjects with long and short stimulus survival times.

When performing stationary tasks under elevated cognitive workload, individuals must perform continual muscle contractions to maintain stability of the body, resulting in fatigue of the postural muscles. When the muscles perform these contractions in a prolonged manner, the body potentially responds through small changes in body movements—micromovements that may lead to discomfort. The study purpose was to evaluate impact of cognitive load on micromovements. The micromovements were measured during three different cognitive workloads; low, medium, and high. The NASA-TLX score was used to evaluate the perceived mental workload and discomfort was assessed by visual analog scale. In total, 60 subjects (30 males and 30 females) were recruited and performed cognitive tasks that simulated flight operations such as changing the radio frequency based on air traffic control messages, balancing the fuel levels in simulated fuel tanks, and aiming a reticle in a designated moving target using the cyclic control. Cognitive load was defined by the frequency of events. Micromovements were defined by changes in the center of pressure (COP) of the seat pan and COP standard deviation. It was found that the high cognitive workloads had the highest NASA-TLX scores including mental demands, temporal demands, and effort. The neck area had the highest overall levels of discomfort followed by upper back. The highest standard deviation for COP shift and number of micromovements occurred for medium cognitive workloads. While there were some interesting trends, few trends reached a statistical significance due to high variability among subjects for the outcome variables.

Objective Assess neck muscle activity for varying interactions between helmet, posture, and visual stress in a simulated “helo-hunch” posture. Background Military aviators frequently report neck pain (NP). Risk factors for NP include head-supported mass, awkward postures, and mental workload. Interactions between these factors could induce constant low-level muscle activation during helicopter flight and better explain instances of NP. Method Interactions between physical loading (helmet doffed/donned), posture (symmetric/asymmetric), and visual stress (low/high contrast) were studied through neck muscle electromyography (EMG), head kinematics, subjective discomfort, perceived workload, and task performance. Subjects ( n = 16) performed eight 30-min test conditions (varied physical loading, posture, and visual stress) while performing a simple task in a simulated “helo-hunch” seating environment. Results Conditions with a helmet donned had fewer EMG median frequency cycles (which infer motor unit rotation for rest/recovery, where more cycles are better) in the left cervical extensor and left sternocleidomastoid. Asymmetric posture (to the right) resulted in higher normalized EMG activity in the right cervical extensor and left sternocleidomastoid and resulted in less lateral bending compared with neutral across all conditions. Conditions with high visual stress also resulted in fewer EMG cycles in the right cervical extensor. Conclusion A complex interaction exists between the physical load of the helmet, postural stress from awkward postures, and visual stress within a simulated “helo-hunch” seating environment. Application These results provide insight into how visual factors influence biomechanical loading. Such insights may assist future studies in designing short-term administrative controls and long-term engineering controls.

Fatigue from prolonged seating with an axial load on the trunk may impair neuromuscular control and spine stability which may elevate risk of low back pain (LBP) for dynamic tasks following seating. The objective of this study was to assess local dynamic trunk stability using the maximum Lyapunov exponent (λMAX) with corresponding coactivation patterns to understand possible effects from prolonged seating. An increase in λMAX would indicate decreased stability. Twenty participants (10 male, 10 female) performed a controlled, cyclic sagittal flexion task at 40 cycles per minute before and after three hours of seating in a simulated helicopter-seating environment with a weighted vest. A statistically significant decrease was seen in λMAX (bits/s) (Pre-Test = 0.654 ± 0.172; Post-Test = 0.829 ± 0.268, p = 0.002), trunk cumulative coactivation index (unitless/s) (Pre-Test = 1.71 ± 0.97; Post-Test = 1.59 ± 0.96, p = 0.0095), and abdominal activation (normalized) (Pre-Test = 0.46 ± 0.17, Post-Test = 0.41 ± 0.18, p = 0.0146) post-seating exposure. Trunk extension was reduced (∼4°, p = 0.0004) during the post-seating cyclic test with slight corresponding increases in flexion. This study provides evidence of potential effects of fatigue from prolonged seating to neuromuscular control, which may have implications for occupations requiring highly dynamic tasks after prolonged seated postures. Future studies would repeat the tests with dynamic environments (i.e., vibration), test the cyclic flexion protocols with different seating interventions, and continue to test the approach to develop a tool to assess back impairment or intervention effectiveness.

BACKGROUND:Motion sickness and low back disorders are prevalent and debilitating conditions that affect the health, performance, and operational effectiveness of military aircrews. This study explored the effects of a motion sickness stimulus on biomechanical and genetic factors that could potentially be involved in the causal pathways for both disorders. METHODS:Subjects recruited from a military population were exposed to either a mild (n = 12) or aggressive (n = 16) motion sickness stimulus in a Neuro-Otologic Test Center. The independent variable of interest was the motion sickness stimulus exposure (before vs. after), though differences between mild and aggressive stimuli were also assessed. Dependent measures for the study included motion sickness exposure duration, biomechanical variables (postural stability, gait function, low back function, lumbar spine loading), and gene expression. FINDINGS:Seven of twelve subjects experiencing the mild motion sickness stimulus endured the full 30 min in the NOTC, whereas subjects lasted an average of 13.2 (SD 5.0) minutes in the NOTC with the aggressive motion sickness stimulus. Mild motion sickness exposure led to a significant decrease in the postural stability measure of sway area, though the aggressive motion sickness exposure led to a statistically significant increase in sway area. Both stimuli led to decreases in low back function, though the decrease was only statistically significant for the mild protocol. Both stimuli also led to significant changes in gene expression. INTERPRETATION:Motion sickness may alter standing balance, decrease low back function, and lead to changes in the expression of genes with roles in osteogenesis, myogenesis, development of brain lymphatics, inflammation, neuropathic pain, and more. These results may provide preliminary evidence for a link between motion sickness and low back disorders.

The creation of stable test phantoms that mimic the scattering characteristics of biological tissue is important for characterizing different Optical imaging methods through biological tissue. Unfortunately utilizing organic materials as tissue test structures pose problems in biomedical imaging research; tissues tend to have short lifetime, change their scattering and other optical characteristics rapidly with time, and are difficult to uses as reliable standards for comparing calibrating imaging systems. To solve these problems ongoing work has shown it is technically possible to create long term stable phantoms which can last for up to 5 years while maintaining consistent optical characteristics which mimic skin characteristics. These long term test phantom is created by encapsulating an intralipid-infused agar layer within clear polymer. Varying the intralipid concentration allows control of the scattering parameters with typical values of µs = 20cm-1, g = 0.95. The phantoms can be created in a wide range of thicknesses and shapes. To characterize these we developed a technique using a digitial camera to capture, in a single measurement, the scattered light from laser beams passing through the test phantoms. Analysis of the image allows hundreds of measurements of scattering values at a wide range of angles using a Matlab program to identify the scattering center and the angular positions. We fitted this to scattering models to extract the µs and g parameters for each test phantom Consistent results were obtained using a Henyey-Greenstein two-term model, probably because the Agar and intralipid impacted the scattering separately.

Objective Develop a coactivation index for the neck and test its effectiveness with complex dynamic head motions. Background Studies describing coactivation for the cervical spine are sparse in the literature. Of those in existence, they were either limited to a priori definitions of agonist/antagonist activity that limited the testing to sagittal and lateral planes or consisted of isometric exertions. Multiplanar movements would allow for a more realistic understanding of naturalistic movements in the cervical spine and propensity for neck pain. However, a gap in the literature exists in which a method to describe coactivation during complex dynamic motions does not exist for the cervical spine. Methods An electromyography-based coactivation index was developed for the cervical spine based on previously tested methodology used on the lumbar spine without a high-end model and tested using a series of different postures and speeds. Results Complex motions involving twisting (i.e., flexion and twisting) and higher speed had higher magnitudes of coactivation than uniplanar motions in the sagittal or lateral plane, which was expected. The coupled motion of flexion and twisting showed four to five times higher coactivation than uniplanar (sagittal or lateral) movements. Conclusion The coactivation index developed accommodates multiplanar, naturalistic movements. Testing of the index showed that motions requiring higher degrees of head control had higher effort due to coactivation, which was expected. Application Overall, this coactivation index may be utilized to understand the neuromuscular effort of various tasks in the cervical spine.

Coactivation is an important component for understanding the physiological cost of muscular and spinal loads and their associations with spinal pathology and potentially myofascial pain. However, due to the complex and dynamic nature of most activities of daily living, it can be difficult to capture a quantifiable measure of coactivation. Many methods exist to assess coactivation, but most are limited to two-muscle systems, isometric/complex analyses, or dynamic/uniplanar analyses. Hence, a void exists in that coactivation has not been documented or assessed as a multiple-muscle system under realistic complex dynamic loading. Overall, no coactivation index has been capable of assessing coactivation during complex dynamic exertions. The aim of this review is to provide an understanding of the factors that may influence coactivation, document the metrics used to assess coactivity, assess the feasibility of those metrics, and define the necessary variables for a coactivation index that can be used for a variety of tasks. It may also be clinically and practically relevant in the understanding of rehabilitation effectiveness, efficiency during task performance, human-task interactions, and possibly the etiology for a multitude of musculoskeletal conditions.

Twenty subjects performed typing tasks on a desktop computer and touch-screen tablet in two chairs for an hour each, and the effects of chair, device, and their interactions on each dependent measure were recorded. Biomechanical measures of muscle force, spinal load, and posture were examined, while discomfort was measured via heart rate variability (HRV) and subjective reports. HRV was sensitive enough to differentiate between chair and device interactions. Biomechanically, a lack of seat back mobility forced individuals to maintain an upright seating posture with increased extensor muscle forces and increased spinal compression. Effects were exacerbated by forward flexion upon interaction with a tablet device or by slouching. Office chairs should be designed with both the human and workplace task in mind and allow for reclined postures to off-load the spine. The degree of recline should be limited, however, to prevent decreased lumbar lordosis resulting from posterior hip rotation in highly reclined postures.

When high-energy cosmic particles hit pixels in digital imagers (cameras) they deposit charges as in CMOS digital circuits. In regular ICs this charge deposition sometimes changes a flip-flop's state, creating a short lived Soft Error or a Single Event Upset (SEU). SEUs are hard to study in ICs as the error is buried within the chip. By comparison in digital camera CMOS Active Pixel Sensor pixels the deposited charge is captured, appearing like illuminated pixel(s) whose value is related directly to the deposited charge. Thus a series of dark field (unilluminated) images records SEU information. Digital camera SEU analysis provides important information about the nature and charge deposited by particle hits, their occurrence rate, and the charge spread area. In this paper we extend the study from 7 μm-4 μm (DSLR cameras) down to 1.2 μm (cell phone) to better understand the SEU process in both digital imagers and regular ICs. As the smallest pixels are found in cell phone imagers special techniques were developed to test these. Tests on multiple phones of 1.34 μm pixels showed SEU rates/cm 2 /s which were ~10X that of the larger pixel imagers. SEUs were mostly confined to single pixels indicating the charge spread was less than 1.34 μm.

BACKGROUND:Many methods exist to describe coactivation between muscles. However, most methods have limited capability in the assessment of coactivation during complex dynamic tasks for multi-muscle systems such as the lumbar spine. The ability to assess coactivation is important for the understanding of neuromuscular inefficiency. In the context of this manuscript, inefficiency is defined as the effort or level of coactivation beyond what may be necessary to accomplish a task (e.g., muscle guarding during postural stabilization). The objectives of this study were to describe the development of an index to assess coactivity for the lumbar spine and test its ability to differentiate between various complex dynamic tasks.METHODS:The development of the coactivation index involved the continuous agonist/antagonist classification of moment contributions for the power-producing muscles of the torso. Different tasks were employed to test the range of the index including lifting, pushing, and Valsalva.FINDINGS:The index appeared to be sensitive to conditions where higher coactivation would be expected. These conditions of higher coactivation included tasks involving higher degrees of control. Precision placement tasks required about 20% more coactivation than tasks not requiring precision, lifting at chest height required approximately twice the coactivation as mid-thigh height, and pushing fast speeds with turning also required at least twice the level of coactivity as slow or preferred speeds.INTERPRETATION:Overall, this novel coactivation index could be utilized to describe the neuromuscular effort in the lumbar spine for tasks requiring different degrees of postural control.

The objective of this study was to evaluate how different workstations may influence physical behavior in office work through motion and how that may affect spinal loads and discomfort. Twenty subjects performed a typing task in three different workstations (seated, standing, and perching) for one hour each. Measures of postural transitions, spinal loads, discomfort, and task performance were assessed in order to understand the effects of workstation interaction over time. Results indicated that standing had the most amount of motion (6–8 shifts/min), followed by perching (3–7 shifts/min), and then seating (<1 shift/min). Standing had the highest reports of discomfort and seating the least. However, spinal loads were highest in A/P shear during standing (190N posterior shear, 407N anterior shear) compared to perching (65N posterior shear, 288N anterior shear) and seating (106N posterior shear, 287 anterior shear). These loads are below the risk threshold for shear, but may still elicit a cumulative response. Perching may induce motion through supported mobility in the perching stool, whereas standing motion may be due to postural discomfort. Office workstation designs incorporating supported movement may represent a reasonable trade-off in the costs-benefits between seating and standing.

The objective of this study was to identify biomechanical measures that can distinguish texting distraction in a laboratory-simulated driving environment. The goal would be to use this information to provide an intervention for risky driving behaviour. Sixteen subjects participated in this study. Three independent variables were tested: task (texting, visual targeting, weighted and non-weighted movements), task direction (front and side) and task distance (close and far). Dependent variables consisted of biomechanical moments, head displacement and the length of time to complete each task. Results revealed that the time to complete each task was higher for texting compared to other tasks. Peak moments during texting were only distinguishable from visual targeting. Peak head displacement and cumulative biomechanical exposure measures indicated that texting can be distinguished from other tasks. Therefore, it may be useful to take into account both temporal and biomechanical measures when considering warning systems to detect texting distraction.

The objective of this study was to identify how physiological measures relate to self-reported vehicle seating discomfort. Twelve subjects of varied anthropometric characteristics were enrolled in the study. Subjects sat in two seats over a 2-h period and were evaluated via three physiological measures (near-infrared spectroscopy, electromyography and pressure mapping) yielding six testing sessions. Subjective discomfort surveys were recorded before and after each session for nine regions of the body. Conditional classification discomfort models were developed through dichotomised physiological responses and anthropometry to predict subjective discomfort in specific body locations. Models revealed that subjects taller than 171 cm with reduced blood oxygenation in the biceps femoris or constant, low-level muscle activity in the trapezius tended to report discomfort in the lower extremities or neck, respectively. Subjects weighing less than 58 kg with reduced blood oxygenation in the biceps femoris or unevenly distributed pressure patterns tended to report discomfort in the buttocks. The sensitivities and specificities of cross-validated models ranged between 0.69 and 1.00. Practitioner Summary: Discomfort has been studied extensively in order to enhance the seating design process. However, biomechanical and physiological responses relative to subjective discomfort have been largely ignored in the literature. Considering these responses along with anthropometry may provide insight into why a specific individual reports a seat as uncomfortable.

OBJECTIVE:The objective of this study was to quantify shoulder muscle fatigue during repetitive exertions similar to motions found in automobile assembly tasks.BACKGROUND:Shoulder musculoskeletal disorders (MSDs) are a common and costly problem in automotive manufacturing.METHOD:Ten subjects participated in the study. There were three independent variables: shoulder angle, frequency, and force. There were two types of dependent measures: percentage change in near-infrared spectroscopy (NIRS) measures and change in electromyography (EMG) median frequency. The anterior deltoid and trapezius muscles were measured for both NIRS and EMG. Also, EMG was collected on the middle deltoid and biceps muscles.RESULTS:The results showed that oxygenated hemoglobin decreased significantly due to the main effects (shoulder angle, frequency, and force). The percentage change in oxygenated hemoglobin had a significant interaction attributable to force and repetition for the anterior deltoid muscle, indicating that as repetition increased, the magnitude of the differences between the forces increased. The interaction of repetition and shoulder angle was also significant for the percentage change in oxygenated hemoglobin. The median frequency decreased significantly for the main effects; however, no interactions were statistically significant.CONCLUSIONS:There was significant shoulder muscle fatigue as a function of shoulder angle, task frequency, and force level. Furthermore, percentage change in oxygenated hemoglobin had two statistically significant interactions, enhancing our understanding of these risk factors.APPLICATION:Ergonomists should examine interactions of force and repetition as well as shoulder angle and repetition when evaluating the risk of shoulder MSDs.