Evaluating Different Measures of Low Back Pain Among U.S. Manual Materials Handling Workers: Comparisons of Demographic, Psychosocial, and Job Physical Exposure.

OBJECTIVE: To examine differences in demographic, psychosocial, and job physical exposure risk factors between multiple low back pain (LBP) outcomes in a prospective cohort of industrial workers. BACKGROUND: LBP remains a leading cause of lost industrial productivity. Different case definitions involving pain (general LBP), medication use (M-LBP), seeking healthcare (H-LBP), and lost time (L-LBP) are often used to study LBP outcomes. However, the relationship between these outcomes remains unclear. METHOD: Demographic, health status, psychosocial, and job physical exposure risk factors were quantified for 635 incident-eligible industrial workers. Incident cases of LBP outcomes and pain symptoms were quantified and compared across the four outcomes. RESULTS: Differences in age, gender, medical history, and LBP history were found between the four outcomes. Most incident-eligible workers (67%) suffered an LBP outcome during follow-up. Cases decreased from 420 for LBP (25.4 cases/100 person-years) to 303 for M-LBP (22.0 cases/100 person-years), to 151 for H-LBP (15.6 cases/100 person-years), and finally to 56 for L-LBP (8.7 cases/100 person-years). Conversely, pain intensity and duration increased from LBP to H-LBP. However, pain duration was relatively lower for L-LBP than for H-LBP. CONCLUSION: Patterns of cases, pain intensity, and pain duration suggest the influence of the four outcomes. However, few differences in apparent risk factors were observed between the outcomes. Further research is needed to establish consistent case definitions. APPLICATION: Knowledge of patterns between different LBP outcomes can improve interpretation of research and guide future research and intervention studies in industry.

Validation of the Revised Strain Index for Predicting Risk of Incident Carpal Tunnel Syndrome in a Prospective Cohort.

The Revised Strain Index (RSI), a model that quantifies physical exposure from individual hand/wrist exertions, tasks, and multi-task jobs, was used to quantify exposure for 1372 incident-eligible manufacturing, service and healthcare workers. Workers were followed for an average of 2.5 years (maximum 6 years) and had an average carpal tunnel syndrome (CTS) incidence rate of 4.6 per 100 person-years. Exceeding the a-priori RSI limit of 10.0 showed increased risk of CTS (Hazard Ratio (HR) = 1.45, 95% CI: 1.11-1.91, p = 0.01). There also was a dose-response relationship using proposed low (RSI ≤ 8.5, HR = 1.00), medium (HR = 1.42 (95% CI: 0.96-2.09, p = 0.08)), and high limits (RSI > 15, HR = 1.79 (95% CI: 1.19-2.69, p = 0.01), respectively. RSI as a continuous variable showed CTS risk increased steadily by between 1.9% and 3.3% per unit increase in RSI (p ≤ 0.03). These results suggest that the RSI is a useful tool for surveillance as well as for job intervention/design and continuous improvement processes.Practitioner Summary The Revised Strain Index (RSI) quantifies physical exposure from individual hand/wrist exertions, tasks, and multi-task jobs. Increased cumulative RSI scores (i.e. daily exposure score) are associated with increased risk of carpal tunnel syndrome (CTS). The RSI is potentially useful as a risk surveillance and intervention design tool.

Changes in Step Characteristics Over a Known Outdoor Surface Transition: The Effect of Parkinson Disease.

The factors that contribute to the difficulties persons with Parkinson Disease (PwPD) have when negotiating transitions in walking surfaces are not completely known. The authors investigated if PwPD adjusted their step characteristics when negotiating a familiar outdoor surface transition between synthetic concrete and synthetic turf. Force plate and motion capture data were collected for 10 participants with mild to moderate Parkinson disease and 5 healthy older control participants ambulating bidirectionally across the transition between synthetic concrete and synthetic turf. Between groups, PwPD had a significantly higher minimum toe clearance (P = .007) for both directions of travel compared with the healthy control group. Within groups, PwPD significantly increased their hip (P < .001) and ankle (P = .016) range of motion walking from concrete to turf, while the healthy control participants significantly increased their minimum toe clearance (P = .013), margin of stability (P = .019), hip (P < .001) and ankle (P = .038) range of motion, and step length (P < .001). Walking from turf to concrete, both the Parkinson disease group (P = .014) and the healthy control group (P < .001) increased their knee range of motion. Both groups adjusted their step characteristics when negotiating known surface transitions, indicating that surface transitions result in step changes regardless of health status. However, PwPD exhibited overcompensations, particularly in their minimum toe clearance.

Risk assessments using the Strain Index and the TLV for HAL, Part II: Multi-task jobs and prevalence of CTS.

The Strain Index (SI) and the American Conference of Governmental Industrial Hygienists (ACGIH) threshold limit value for hand activity level (TLV for HAL) have been shown to be associated with prevalence of distal upper-limb musculoskeletal disorders such as carpal tunnel syndrome (CTS). The SI and TLV for HAL disagree on more than half of task exposure classifications. Similarly, time-weighted average (TWA), peak, and typical exposure techniques used to quantity physical exposure from multi-task jobs have shown between-technique agreement ranging from 61% to 93%, depending upon whether the SI or TLV for HAL model was used. This study compared exposure-response relationships between each model-technique combination and prevalence of CTS. Physical exposure data from 1,834 workers (710 with multi-task jobs) were analyzed using the SI and TLV for HAL and the TWA, typical, and peak multi-task job exposure techniques. Additionally, exposure classifications from the SI and TLV for HAL were combined into a single measure and evaluated. Prevalent CTS cases were identified using symptoms and nerve-conduction studies. Mixed effects logistic regression was used to quantify exposure-response relationships between categorized (i.e., low, medium, and high) physical exposure and CTS prevalence for all model-technique combinations, and for multi-task workers, mono-task workers, and all workers combined. Except for TWA TLV for HAL, all model-technique combinations showed monotonic increases in risk of CTS with increased physical exposure. The combined-models approach showed stronger association than the SI or TLV for HAL for multi-task workers. Despite differences in exposure classifications, nearly all model-technique combinations showed exposure-response relationships with prevalence of CTS for the combined sample of mono-task and multi-task workers. Both the TLV for HAL and the SI, with the TWA or typical techniques, appear useful for epidemiological studies and surveillance. However, the utility of TWA, typical, and peak techniques for job design and intervention is dubious.

Risk assessments using the Strain Index and the TLV for HAL, Part I: Task and multi-task job exposure classifications.

BACKGROUND: The Strain Index (SI) and the American Conference of Governmental Industrial Hygienists (ACGIH) Threshold Limit Value for Hand Activity Level (TLV for HAL) use different constituent variables to quantify task physical exposures. Similarly, time-weighted-average (TWA), Peak, and Typical exposure techniques to quantify physical exposure from multi-task jobs make different assumptions about each task's contribution to the whole job exposure. Thus, task and job physical exposure classifications differ depending upon which model and technique are used for quantification. This study examines exposure classification agreement, disagreement, correlation, and magnitude of classification differences between these models and techniques. METHODS: Data from 710 multi-task job workers performing 3,647 tasks were analyzed using the SI and TLV for HAL models, as well as with the TWA, Typical and Peak job exposure techniques. Physical exposures were classified as low, medium, and high using each model's recommended, or a priori limits. Exposure classification agreement and disagreement between models (SI, TLV for HAL) and between job exposure techniques (TWA, Typical, Peak) were described and analyzed. RESULTS: Regardless of technique, the SI classified more tasks as high exposure than the TLV for HAL, and the TLV for HAL classified more tasks as low exposure. The models agreed on 48.5% of task classifications (kappa = 0.28) with 15.5% of disagreement between low and high exposure categories. Between-technique (i.e., TWA, Typical, Peak) agreement ranged from 61-93% (kappa: 0.16-0.92) depending on whether the SI or TLV for HAL was used. CONCLUSIONS: There was disagreement between the SI and TLV for HAL and between the TWA, Typical and Peak techniques. Disagreement creates uncertainty for job design, job analysis, risk assessments, and developing interventions. Task exposure classifications from the SI and TLV for HAL might complement each other. However, TWA, Typical, and Peak job exposure techniques all have limitations. Part II of this article examines whether the observed differences between these models and techniques produce different exposure-response relationships for predicting prevalence of carpal tunnel syndrome.

Relationships between job organisational factors, biomechanical and psychosocial exposures.

The relationships between work organisational, biomechanical and psychosocial factors were studied using cross-sectional data from a pooled dataset of 1834 participants. The work organisational factors included: job rotation, overtime work, having second jobs and work pace. Task and job level biomechanical variables were obtained through sub-task data collected in the field or analysed in the laboratory. Psychosocial variables were collected based on responses to 10 questions. The results showed that job rotations had significant effects on all biomechanical and most psychosocial measures. Those with job rotations generally had higher job biomechanical stressors, and lower job satisfaction. Overtime work was associated with higher job biomechanical stressors, and possibly self-reported physical exhaustion. Those having second jobs reported getting along with co-workers well. Work pace had significant influences on all biomechanical stressors, but its impact on job biomechanical stressors and psychosocial effects are complicated. PRACTITIONER SUMMARY: The findings are based on a large number of subjects collected by three research teams in diverse US workplaces. Job rotation practices used in many workplaces may not be effective in reducing job biomechanical stressors for work-related musculoskeletal disorders. Overtime work is also associated with higher biomechanical stressors.

The effect of ergonomic laparoscopic tool handle design on performance and efficiency.

BACKGROUND: Many factors can affect a surgeon's performance in the operating room; these may include surgeon comfort, ergonomics of tool handle design, and fatigue. A laparoscopic tool handle designed with ergonomic considerations (pistol grip) was tested against a current market tool with a traditional pinch grip handle. The goal of this study is to quantify the impact ergonomic design considerations which have on surgeon performance. We hypothesized that there will be measurable differences between the efficiency while performing FLS surgical trainer tasks when using both tool handle designs in three categories: time to completion, technical skill, and subjective user ratings. METHODS: The pistol grip incorporates an ergonomic interface intended to reduce contact stress points on the hand and fingers, promote a more neutral operating wrist posture, and reduce hand tremor and fatigue. The traditional pinch grip is a laparoscopic tool developed by Stryker Inc. widely used during minimal invasive surgery. Twenty-three (13 M, 10 F) participants with no existing upper extremity musculoskeletal disorders or experience performing laparoscopic procedures were selected to perform in this study. During a training session prior to testing, participants performed practice trials in a SAGES FLS trainer with both tools. During data collection, participants performed three evaluation tasks using both handle designs (order was randomized, and each trial completed three times). The tasks consisted of FLS peg transfer, cutting, and suturing tasks. RESULTS: Feedback from test participants indicated that they significantly preferred the ergonomic pistol grip in every category (p < 0.05); most notably, participants experienced greater degrees of discomfort in their hands after using the pinch grip tool. Furthermore, participants completed cutting and peg transfer tasks in a shorter time duration (p < 0.05) with the pistol grip than with the pinch grip design; there was no significant difference between completion times for the suturing task. Finally, there was no significant interaction between tool type and errors made during trials. CONCLUSIONS: There was a significant preference for as well as lower pain experienced during use of the pistol grip tool as seen from the survey feedback. Both evaluation tasks (cutting and peg transfer) were also completed significantly faster with the pistol grip tool. Finally, due to the high degree of variability in the error data, it was not possible to draw any meaningful conclusions about the effect of tool design on the number or degree of errors made.

The strain index and TLV for HAL: risk of lateral epicondylitis in a prospective cohort.

BACKGROUND: This study's objective was to quantify exposure-response relationships between job physical exposure (JPE) and incidence of lateral epicondylitis (LE). METHODS: A cohort of 536 workers was enrolled from 10 manufacturing facilities and followed monthly for 6 years to ascertain changes in JPE and health status. JPE was individually measured and quantified using the Strain Index (SI) and TLV for HAL. Worker demographics, medical history, psychosocial factors, and current musculoskeletal disorders were obtained. RESULTS: Fifty-six workers developed LE. In multivariate models JPE, age, family problems, and swimming were associated with increased risk of LE. SI showed an exposure-response relationship with maximum hazard ratio (HR) of 4.5(P = 0.04). TLV for HAL showed a non-statistically significant trend for increased risk of LE (P = 0.19). CONCLUSION: JPE is associated with increased risk of LE. The SI and TLV for HAL are useful metrics for estimating JPE.

The Impact of Design Factors on User Behavior in a Virtual Hospital Room to Explore Fall Prevention Strategies.

OBJECTIVES: Falls in hospitals pose a significant safety risk, leading to injuries, prolonged hospitalization, and lasting complications. This study explores the potential of augmented reality (AR) technology in healthcare facility design to mitigate fall risk. BACKGROUND: Few studies have investigated the impact of hospital room layouts on falls due to the high cost of building physical prototypes. This study introduces an innovative approach using AR technology to advance methods for healthcare facility design efficiently. METHODS: Ten healthy participants enrolled in this study to examine different hospital room designs in AR. Factors of interest included room configuration, door type, exit side of the bed, toilet placement, and the presence of IV equipment. AR trackers captured trajectories of the body as participants navigated through these AR hospital layouts, providing insights into user behavior and preferences. RESULTS: Door type influenced the degree of backward and sideways movement, with the presence of an IV pole intensifying the interaction between door and room type, leading to increased sideways and backward motion. Participants displayed varying patterns of backward and sideways travel depending on the specific room configurations they encountered. CONCLUSIONS: AR can be an efficient and cost-effective method to modify room configurations to identify important design factors before conducting physical testing. The results of this study provide valuable insights into the effect of environmental factors on movement patterns in simulated hospital rooms. These results highlight the importance of considering environmental factors, such as the type of door and bathroom location, when designing healthcare facilities.

The effect of time to amputation on medical costs accrued during the first twelve months after injury-A California workers' compensation claims study.

BACKGROUND: This study investigated whether the time to amputation (TtoA) after a work-related injury had a significant effect on the medical costs accrued in the first year after injury. DATA SOURCE: Six thousand nine hundred fifty-three person-level workers' compensation claims data from the state of California, USA, from 2007 to 2018. METHODS: Multiple quantile regression was used to assess the impact of TtoA on medical costs accrued during the first 12 months after injury. Three time intervals for TtoA were investigated: immediate (0, 1 days), short-delay (2-31 days), and long-delay (>31 days). RESULTS: The median (interquartile range) medical dollars paid per claim during the first 12 months for the study population was $12,414 ($6,324-$29,347). Amputations that occurred during the short-delay time interval resulted in significant ( p < 0.001) median (95% CI) savings of -$3,196 (-$3,968 to -$2,424) compared with the immediate amputation group. The long-delay time interval resulted in significantly ( p < 0.001) increased median (95% CI) spending of $5,613 ($4,675-$6,551) compared with the immediate amputation group. Covariates that significantly increased costs were medical intensity, medical complexity, use of a prosthesis, and if the injured worker pursued legal action in addition to a workers' compensation claim. CONCLUSIONS: This study presents the impact of TtoA on medical spending in the first year after a work-related injury that results in an amputation. Amputations that occurred within the first month after an injury resulted in reduced medical spending compared with immediate amputations, and amputations that occurred after the first month resulted in increased medical spending.

Axial muscle activation provides stabilization against perturbations while running.

Incidence of traumatic brain injury is an important hazard in sports and recreation. Unexpected (blind-sided) impacts with other players, obstacles, and the ground can be particularly dangerous. We believe this is partially due to the lack of muscular activation which would have otherwise provided protective bracing. In this study participants were asked to run on the treadmill while undergoing perturbations applied at the waist which pulled participants in the fore-aft and lateral directions. To determine the effect of unexpected impacts, participants were given a directional audio-visual warning 0.5 s prior to the perturbation in half of the trials and were unwarned in the other half of the trials. Perturbations were given during the start of the stance phase and during the start of the flight phase to examine two distinct points within the locomotor cycle. Muscle activity was monitored in axial muscles before, during, and after the perturbations were given. We hypothesized that the presence of a warning would allow for voluntary axial muscle activity prior to and during perturbations that would provide bracing of the body, and decreased displacement and acceleration of the head compared to unwarned perturbations. Our results indicate that when a warning is given prior to perturbation, the body was displaced significantly less, and the linear acceleration of the head was also significantly lessened in response to some perturbations. The perturbations given in this study caused significant increases in axial muscle activity compared to activity present during control running. We found evidence that cervical and abdominal muscles increased activity in response to the warning and that typically the warned trials displayed a lower reflexive muscle activity response. Additionally, we found a stronger effect of the warnings on muscle activity within the perturbations given during flight phase than those given at stance phase. Results from this study support the hypothesis that knowledge regarding an impending perturbation is used by the neuromuscular system to activate relevant core musculature and provide bracing to the athlete.

Cardiovascular Disease Risk Factors Predict the Development and Numbers of Common Musculoskeletal Disorders in a Prospective Cohort.

OBJECTIVE: The aim of the study is to assess risk of common musculoskeletal disorders (MSDs) based on cardiovascular disease (CVD) risk scores. METHODS: Data from a 9-year prospective cohort of 1224 workers in three states were analyzed. Baseline data included questionnaires, structured interviews, physical examinations, anthropometric measurements, nerve conduction studies, and individualized measurement of job physical factors. Monthly follow-ups were conducted. Framingham risk scores were calculated. A priori case definitions were constructed for carpal tunnel syndrome, lateral epicondylopathy, medial epicondylopathy, and rotator cuff tendinopathy. RESULTS: Adjusted RRs for one or more MSDs increased to 3.90 (95% confidence interval, 2.20-6.90) among those with 10-year cardiovascular disease risk scores greater than 15% and 17.4 (95% confidence interval, 3.85-78.62) among those with more than 4 disorders. CONCLUSIONS: Cardiovascular disease factors are strongly associated with the subsequent development of common MSDs. Risks among those with multiple MSDs are considerably stronger.

Motorized Robotic Closed Cervical Traction: Biomechanical Proof of Concept.

STUDY DESIGN: Biomechanical study. OBJECTIVE: To demonstrate that robotic cervical traction can apply closed cervical traction as effectively as manual weight-and-pulley traction in extension spring and cadaveric models. SUMMARY OF BACKGROUND DATA: Closed cervical traction is used to reduce subaxial cervical spine dislocation injuries and to distract the intervertebral space during cervical spine surgery. Weight-and-pulley cervical traction relies on cumbersome and imprecise technology without any safeguard to prevent over-traction or weights being pulled/released inadvertently. METHODS: A prototype robotic traction device was designed and manufactured by the authors with real-time tensile force measurement, ±1-lbs (5 N) force application accuracy, locking/non-backdriveable linear actuators with actuator position sensing, 200-lbs (900 N) maximum force capability, up to 20° of flexion/extension manipulation, <25-lbs (111 N) device weight, and compatibility with Gardner-Wells tongs or Mayfield head clamp. The device was tested using an extension spring model and an intact fresh cadaver specimen to assess applied and desired force over time and radiographic changes in the cervical spine as traction force increased. The cadaver was tested in manual traction initially and then robotic traction in 10-lbs (50 N) increments up to 80-lbs (355 N) to compare methods. RESULTS: The prototype device met or exceeded all requirements. In extension spring testing, the device reached the prescribed forces of both 25-lbs (111 N) and 80-lbs (355 N) accurately and maintained the desired weight. In cadaveric testing, radiographic outcomes were equivalent between the prototype and manual weight-and-pulley traction at 80-lbs (355 N; disk space measurements within ±10% for all levels), and the device reached the desired weight within±1-lbs (5 N) of accuracy at each weight interval. CONCLUSION: This preliminary work demonstrates that motorized robotic cervical traction can safely and effectively apply controlled traction forces.

Classifying hazardous movements and loads during manual materials handling using accelerometers and instrumented insoles.

Improper manual material handling (MMH) techniques are shown to lead to low back pain, the most common work-related musculoskeletal disorder. Due to the complex nature and variability of MMH and obtrusiveness and subjectiveness of existing hazard analysis methods, providing systematic, continuous, and automated risk assessment is challenging. We present a machine learning algorithm to detect and classify MMH tasks using minimally-intrusive instrumented insoles and chest-mounted accelerometers. Six participants performed standing, walking, lifting/lowering, carrying, side-to-side load transferring (i.e., 5.7 kg and 12.5 kg), and pushing/pulling. Lifting and carrying loads as well as hazardous behaviors (i.e., stooping, overextending and jerky lifting) were detected with 85.3%/81.5% average accuracies with/without chest accelerometer. The proposed system allows for continuous exposure assessment during MMH and provides objective data for use with analytical risk assessment models that can be used to increase workplace safety through exposure estimation.

Upper-extremity kinematics and interlimb movement correlation in persons with Parkinson Disease on irregular terrain, cross-slope, and under dual-task condition.

Background: A defining clinical characteristics of Parkinson disease is reduced upper-extremity movements. Irregular terrain, the presence of a cross slope, and dual-task conditions have been found to alter the lower-limb gait characteristics of persons with Parkinson disease but there is little information how different environmental and cognitive conditions impact upper-limb kinematics as well as interlimb movement correlation. Research question: Do environmental conditions, such as irregular terrain and the presence of cross slope, as well as dual-task condition impact the upper-extremity kinematics and interlimb movement correlation of persons with Parkinson disease compared to healthy, age-matched controls? Methods: Three-dimensional whole-body gait data were collected for nine participants with mild-to-moderate Parkinson disease and nine healthy age-matched control participants. All participants ambulated on a regular terrain, irregular terrain, with and without cross slope, and under dual and single-task conditions. The primary outcomes were arm swing magnitude, arm swing asymmetry, and normalized cross-correlation between the ipsilateral arms and contralateral legs, which characterized movement correlation. Results: For all conditions, persons with Parkinson disease exhibited reduced arm swing magnitude and greater arm swing asymmetry compared to the healthy controls. All participants increased their arm swing magnitude on the irregular surface and under the dual-task condition. In the healthy group, the arm swing asymmetry was invariant to terrain but declined under the dual-task condition while the persons with Parkinson disease exhibited increased asymmetry on the cross slope, on the irregular terrain, and under the dual-task condition. Interlimb movement correlation decreased on the irregular terrain for the persons with Parkinson disease while the healthy group exhibited decreased interlimb movement correlation on the cross slope as well as under the dual-task condition. Significance: Persons with Parkinson disease were able to increase their arm swing magnitude when their balance was challenged and the most significant threat to their safety as defined by the greatest reduction in the interlimb movement correlation was the irregular terrain.

Regulation of whole-body and segmental angular momentum in persons with Parkinson's disease on an irregular surface.

BACKGROUND: Persons with Parkinson's disease have impaired motor control that increases their chance of falling when walking, especially on difficult terrains. This study investigated how persons with Parkinson's disease regulate their dynamic balance on a regular and an irregular surface. METHODS: Nine participants with Parkinson's disease and nine healthy, age-matched control participants ambulated on both a regular and an irregular surface. Whole-body and segmental angular momenta were calculated using three-dimensional motion capture data. Major modes of variability between health groups on the two surfaces were investigated using principal component analysis, while differences within each health group between surfaces was investigated using statistical parametric mapping t-tests. FINDINGS: Between groups, the Parkinson participants had greater sagittal, frontal, and transverse whole-body angular momentum on both surfaces, primarily following heel-strike, and the magnitude difference on the irregular surface was greater than on the regular surface. The greatest between group segmental differences on the irregular compared to the regular surface were the legs in the sagittal plane and the head/trunk/pelvis in the transverse plane, with the Parkinson group having greater magnitudes. The within-group comparison found the Parkinson participants had poorer regulation of whole-body angular momentum in the sagittal plane, while the healthy participants showed no consistent differences between surfaces. INTERPRETATION: On an irregular surface, persons with Parkinson's disease exhibit poor control of dynamic balance in the frontal and sagittal planes. These results emphasize the need for weight transfer techniques and training in both the sagittal and frontal planes to maximize balance and reduce fall risk.

The role of neck muscle co-contraction and postural changes in head kinematics after safe head impacts: Investigation of head/neck injury reduction.

Concerns surrounding concussions from impacts to the head necessitate research to generate new knowledge about ways to prevent them and reduce risk. In this paper, we report the relative temporal characteristics of the head resulting from neck muscle co-contraction and postural changes following a sudden force applied to the head in four different directions. In the two "prepared" conditions (i.e., co-contraction and postural), participants experienced impulsive forces to the head after hearing a warning. The warning given for the postural condition informed both the direction and timing of the impulsive force. Participants responded to the postural warning by altering their head posture, whereas in the co-contraction warning, the force direction was unknown to them, and they were asked to isometrically co-contract their neck muscles after the warning. Peak angular velocity reduced by 29% in sagittal extension, 18% in sagittal flexion, and 23% in coronal lateral flexion in prepared vs. unwarned conditions. Peak linear acceleration was attenuated by 15% in sagittal extension, 8% in sagittal flexion, and 18% in coronal lateral flexion in prepared vs. unwarned conditions. Changes in peak angular acceleration were not uniform. We also measured a significant delay in the peak angular velocity (22 vs. 44.8 ms) and peak angular acceleration (7 vs. 20 ms) after peak linear acceleration in prepared compared to unwarned conditions. An increase in muscle activation significantly reduced the peak angular velocity and linear acceleration. Gross head movement was significantly decreased with preparation. These findings suggest that a warning prior to impact can reduce head kinematics associated with injury.

Cervical Muscle Activation Due to an Applied Force in Response to Different Types of Acoustic Warnings.

Mild traumatic brain injury (mTBI) and whiplash-associated disorder are the most common head and neck injuries and result from a sudden head or body acceleration. The head and neck injury potential is correlated with the awareness, level of muscle activation, and posture changes at the time of the perturbation. Environmental acoustic stimuli or a warning system can influence muscle activation and posture during a head perturbation. In this study, different acoustic stimuli, including Non-Directional, Directional, and Startle, were provided 1000 ms before a head impact, and the amplitude and timing of cervical muscle electromyographic (EMG) data were characterized based on the type of warning. The startle warning resulted in 49% faster and 80% greater EMG amplitude compared to the Directional and Non-Directional warnings after warning and before the impact. The post-impact peak EMG amplitudes in Unwarned trials were lower by 18 and 21% in the retraction and rebound muscle groups, respectively, compared to any of the warned conditions. When there was no warning before the impact, the retraction and rebound muscle groups also reached their maximum activation 38 and 54 ms sooner, respectively, compared to the warned trials. Based on these results, the intensity and complexity of information that a warning sound carries change the muscle response before and after a head impact and has implications for injury potential.

Trends in incidence and correlation between medical costs and lost workdays for work-related amputations in the State of California from 2007 to 2018.

BACKGROUND: Detailed information regarding workers who experience an amputation in the workplace over the last decade is limited. To better understand the financial and functional impact of a work-related amputation, this study quantifies the incidence of work-related amputations in the California workforce from 2007 to 2018 as well as the relationship between medical costs and lost workdays as a function of amputation level. METHODS: Workers' compensation claims data from California spanning the years 2007 to 2018 were evaluated to describe trends in amputation incidence (N = 16 931). Quartile values for medical costs, indemnity costs, and lost workdays were reported as a function of amputation level. Correlations were performed between medical costs and lost workdays to examine their relationship. RESULTS: The average incidence from 2007 to 2018 was 8.9 (95% CI 8.5, 9.4) amputations per 100 000 workers. There was a significant spike in amputations in 2008. Partial-hand amputations were the most common with 73.3 (95% CI 69.2, 77.7) cases per 1 000 000 workers, and the industry with the highest incidence was construction with 26.0 (95% CI 22.4, 30.0) cases per 100 000 workers. Overall, medical costs were moderately correlated with lost workdays (Spearman's rho = 0.51), and that level of correlation remained relatively consistent across all levels of amputation (Spearman's rho = 0.48-0.62). CONCLUSIONS: Amputations represent high medical costs and number of lost workdays. Considering the type of amputation and the industry the injury occurred in is important in order to work toward returning this population to work. Our results present the status of amputations in the California workplace and establish a basis for using medical costs to infer lost work productivity for this population.

Cervical Muscle Activation Characteristics and Head Kinematics in Males and Females Following Acoustic Warnings and Impulsive Head Forces.

Sex, head and neck posture, and cervical muscle preparation are contributing factors in the severity of head and neck injuries. However, it is unknown how these factors modulate the head kinematics. In this study, twenty-four (16 male and 8 female) participants experienced 50 impulsive forces to their heads with and without an acoustic warning. Female participants demonstrated a 71 ms faster (p = 0.002) muscle activation onset compared to males after warning. The magnitude of muscle activation was not significant between sexes. Females exhibited 21% (p < 0.008) greater peak angular velocity in all force directions and 18% (p < 0.04) greater peak angular acceleration in sagittal plane compared to males. Females exhibited 15% (p = 0.03) greater peak linear acceleration compared to males only in sagittal flexion. Preparation attenuated head kinematics significantly (p < 0.03) in 11 out of 18 investigated head kinematics for both sexes. A warning eliciting a startle response 420 ms prior to the impact resulted in significant attenuation of all measured head kinematics in sagittal extension (p < 0.037). In conclusion, both sex and warning type were significant factors in head kinematics. These data provide insight into the complex relationship of muscle activation and sex, and may help identify innovative strategies to reduce head and neck injury risk in sports.