Exploring the link between occupationally relevant whole body vibration and headache and neck pain: is elevated muscle tension an intermediary factor?

Whole body vibration (WBV) is linked to short- and longer-term adverse health outcomes, including cognitive impairment, stress and memory loss, loss of balance, reduced proprioception, visual and vestibular disturbances, gastrointestinal problems, and musculoskeletal disorders. Epidemiological evidence supports the link between WBV and headache and head discomfort, but few experimental studies have examined this relationship, particularly with increased muscle tension, as an intermediary. This study aimed to investigate the relationship between muscle tension and vibration intensity, between perceived neck pain and headache/head discomfort and vibration intensity, and between muscle tension and reported neck pain and headache symptoms from simulated WBV based on field measurements of all-terrain vehicle operation on farm terrain. We observed significantly higher electromyography amplitude in the High condition (equivalent to EU Directive's Exposure Limit Value) compared to both Low (equivalent to EU Directive's Exposure Action Value) and Control (quiet sitting) conditions at the left upper trapezius muscle but there were no significant time effects. Neck pain and headache/head discomfort significantly increased after both Low (91% increase from baseline) and High (154% increase from baseline) vibration conditions but there were no significant differences between conditions. Based on simple regression modeling, the relationship between muscle activity and neck pain or headache was very weak (R2 = 0-0.093). Given the possibility of multiple factors contributing to headache symptoms, future research should not only consider the role of muscle tension but also sensory conflict, excessive noise, biodynamic responses, and a combination of these factors.

Towards in-field assessment of humeral and scapular kinematics: a comparison between laboratory and field settings using inertial sensors.

Introduction: Inertial measurement units allow for quantitative assessment of body motion in many environments. Determining the ability to measure upper limb motion with inertial measurement units, leveraging procedures traditionally used in the lab such as scapular calibration procedures and humeral axial rotation calculation, would expand the opportunities to assess upper limb function in externally valid environments. This study examined if humeral and scapular motion measured in different field settings is consistent with motion measured in a lab setting in similar tasks. Methods: Twenty-eight adults participated in the study (14 field setting, 14 lab setting). Three different types of field settings were included: home (n = 5), work (n = 4), and sports (n = 5). Field participants were matched to lab participants based on sex and body height. All participants were equipped with five inertial and magnetic measurement units (Xsens Awinda, Xsens Technlogies, NL, Fs = 100 Hz) on the torso, humeri, and scapulae. Humeral and scapular angles were measured during a functional task protocol consisting of seven tasks. Data from all three field settings were combined. Statistical parametric mapping (α = .05) was used to assess differences in waveforms between the lab and field data. Results and discussion: Five out of seven tasks displayed no differences for humeral elevation and humeral axial rotation, while scapular upward rotation and tilt were not statistically different for any tasks. Scapular internal rotation variability was very high for the field setting, but not for the lab setting. Task-based differences in humeral elevation and humeral axial rotation may be related to equipment modifications for the field protocol and between subjects' variability in task performance. Data indicate that humeral elevation, humeral axial rotation, and scapular upward rotation can be measured in externally valid field settings, which is promising for the evaluation of upper limb movement in natural environments.

Do Sex and Age Influence Scapular and Thoracohumeral Kinematics During a Functional Task Protocol?

There is mixed evidence on the role that biological sex plays in shoulder biomechanics despite known differences in musculoskeletal disorder prevalence between males and females. Additionally, advancing age may contribute to shoulder kinematic changes. The purpose of this study was to determine if sex and age influenced scapular and thoracohumeral kinematics during a range of functional tasks. Sixty healthy participants aged 19-63 years (30 males; 30 females) completed a functional task protocol while their upper limb motion was recorded. Scapular and humeral angles were calculated and compared with multiple linear regressions to assess the interaction effects of sex and age. Shoulder kinematics were not different between sex and age groups for many of the functional tasks. However, females had lower humeral external rotation in the overhead lift task (15°, P < .001), and less scapular anterior tilt angles in the forward transfer task (6°, P < .001) than males. Age was positively associated with humeral elevation (R2 = .330, P < .001) and scapular rotation (R2 = .299, P < .001) in the Wash Axilla task. There exist some kinematic differences between sex and with advancing age for select functional tasks, which should be considered for musculoskeletal disorder development.

Does calibration pose improve scapular kinematic repeatability in functional tasks?

Tracking scapular motion can be challenging. More research is needed to determine the best practices for scapular measurement in multi-planar tasks. The purpose of this study was to compare the repeatability of scapular kinematics during a functional task protocol calculated from different calibration procedures. It was hypothesized that select poses would improve repeatability in specific tasks. The torso, humerus, and scapula were tracked with optical motion capture in two sessions for ten pain-free participants. Scapular calibrations were completed in five poses: neutral, maximum elevation, 90° abduction, hand to contralateral shoulder, and hand to back. Each participant completed eight functional tasks (Comb Hair, Wash Axilla, Tie Apron, Overhead Reach, Side Reach, Forward Transfer, Floor Lift, Overhead Lift). Scapular angles were calculated with five different calibration procedures and extracted at 30° increments of humeral elevation in each task. Mean difference, limits of agreement, intraclass correlations, and minimal detectable change (MDC) were calculated for each task and elevation level. The inclusion of different calibration poses did not markedly improve outcomes over the maximum elevation double calibration for most tasks. Using this calibration procedure, median MDCs were 10.0° for upward rotation, 13.7° for internal rotation, and 9.8° for tilt.

Defining humeral axial rotation with optical motion capture and inertial measurement units during functional task assessment.

Humeral motion can be challenging to measure and analyze. Typically, Euler/Cardan sequences are used for humeral angle decomposition, but choice of rotation sequence has substantial effects on outcomes. A new method called True axial rotation calculation may be more precise. The objective of this study is to compare humeral axial rotation measured from two systems (optical motion capture and inertial measurement units (IMUs)) and calculated with two methods (Euler angles and True axial). Motion of torso and dominant humerus of thirty participants free from any upper limb impairments was tracked using both systems. Each participant performed a functional tasks protocol. Humeral axial rotation was calculated with Euler decomposition and the True axial method. Waveforms were compared with two-way ANOVA statistical parametric mapping. A consistent pattern emerged: axial rotation was not different between motion capture systems when using the True axial method (p > .05), but motion capture systems showed relatively large magnitude differences (~ 20-30°) when using Euler angle calculation. Between-calculation method differences were large for both motion capture systems. Findings suggest that the True axial rotation method may result in more consistent findings that will allow for precise measurements and comparison between motion capture systems. Two methods for calculating humeral axial rotation measured from optical motion capture and inertial measurement units were compared.

Defining repeatability for scapulothoracic and thoracohumeral motion during the novel work-related activities and functional task (WRAFT) protocol.

Upper limb motion can be challenging to measure and analyze during work or daily life tasks. Further, humeral angle calculation method substantially influences angle outcomes. Therefore, the purpose of this study was to assess the repeatability of scapular and humeral kinematics and compare thoracohumeral angle calculation during a work-related and functional task (WRAFT) protocol. Thirty healthy young adults completed the WRAFT protocol (Comb Hair, Wash Axilla, Tie Apron, Overhead Reach, Side Reach, Forward Transfer, Floor Lift, and Overhead Lift) on two separate occasions. Peak humeral angles and select scapular angles were extracted for each task. Intra-class correlation coefficients (ICCs), standard error of measurement, and minimal detectable change (MDC) were examined. Humeral angles were compared using the XZY and ZXY rotation sequences and "true" axial rotation for incidence of gimbal lock and amplitude coherence. Results showed that for scapular kinematics, elevation-based WRAFTs produced overall better ICC scores (0.23-0.90) compared to those tasks primarily driven by lateral humeral motion (0.02-0.84). MDCs ranged from 7°-78°, suggesting some tasks demonstrated good repeatability (Comb Hair, Overhead Reach, Floor Lift), while others had very high variability (Side Reach, Tie Apron). Amplitude coherence for thoracohumeral angles was best for ZXY for all tasks except the Comb Hair and Tie Apron, for which XZY is recommended. "True" axial rotation demonstrated good coherence for all but Tie Apron. The WRAFT protocol may be used for functionally relevant scapular and humeral kinematic assessment for select task and posture combinations.

Comparison of scapular kinematics from optical motion capture and inertial measurement units during a work-related and functional task protocol.

Understanding scapular motion during everyday tasks is essential for adequate return-to-work and intervention programming, yet most scapular assessments involve restricted motion analysis within a laboratory setting. Inertial measurement units (IMUs) have been used to track scapular motion, but their validity compared to "gold standard" optical motion capture is not well defined. Further, it is unclear how different IMU sensor placements could affect scapular kinematic outcomes during a functional task protocol. To assess the reliability of scapular motion measurements with the use of the "gold standard" optical motion capture and IMUs, and to compare scapular IMU placement to assess which location (acromion or spine) was best for reliability of scapular motion, participants completed two testing sessions. During each lab visit, participant torso, humeri, and scapulae motion was tracked during 3 trials of 8 dynamic tasks and two elevation movements. Scapular angles were extracted during each task. To assess intra-session reliability, intra-class correlation coefficients (ICCs), and root mean square errors (RMSEs) were calculated. Results showed ICCs and RMSEs were acceptable. Although there appeared offsets between the two motion capture system scapular kinematics outcomes based on the plotted waveforms, the movement patterns appeared consistent between both motion capture methods. Data also showed that acromion IMU placement produced slightly more reliable outcomes than placement on the spine. Two placements of scapular tracking IMUs were tested with identical procedures.

An Investigation of Bilateral Symmetry in Softball Pitchers According to Body Composition.

Introduction: High body fat percentage (bf%) is considered a potential injury risk factor for softball pitchers amidst the already high rates of pitching-related injury. Similarly, research points out that large bilateral asymmetries are another risk factor for softball pitchers. As softball pitching is a highly asymmetric sport and the repetitive nature of the windmill pitch places high stress on the body while pitchers are in unbalanced and asymmetric positions, research examining body composition and asymmetry is necessary. Purpose: The purpose of this study was to compare functional characteristics of softball pitchers with a healthy and a high bf%. Bilateral symmetry was assessed for pitchers' hip and shoulder isometric strength (ISO) and range of motion (ROM) between the following two groups of softball pitchers: (1) those with a high bf% (≥32%) and (2) those with a healthy bf% (<32%). Methods: A total of 41 high school female softball pitchers from the southern United States agreed to participate (1.69 ± 0.07 m, 76.14 ± 17.08 kg, 15.1 ± 1.1 years). Pitchers completed a dual-energy X-ray absorptiometry (DEXA) scan and were grouped into one of the following two categories based on their bf%: healthy (<32 bf%) and high (≥32 bf%). Bilateral symmetry was assessed for pitchers' hip and shoulder ISO and ROM using a handheld dynamometer and inclinometer, respectively. Bilateral arm bone and lean mass was also measured via the DEXA. Results: Mixed analyses of variance revealed a significant interaction between bf% groups and side dominance for internal rotation shoulder ROM, F(1, 39) = 14.383, p < 0.001, η2 p = 0.269. Main effects for side dominance were also observed for shoulder external rotation ISO, F(1, 39) = 8.133, p = 0.007, η2 p = 0.173, hip internal rotation ISO, F(1, 39) = 4.635, p = 0.038, η2 p = 0.106, arm bone mass, F(1, 39) = 38.620, p < 0.001, η2 p = 0.498, and arm lean mass, F(1, 39) = 101.869, p < 0.001, η2 p = 0.723. Conclusion: Asymmetries and slight differences in functional characteristics exist between bf% groups. Altered functional characteristics may influence pitchers' windmill pitch movement and should be acknowledged by support staff to improve softball pitchers' health and longevity. Implications: Insight into asymmetries can help researchers and clinicians understand the implication of excess body fat and further theorize mechanisms of injury among this athlete population.

Effect of Breast Reconstruction on Kinematics and Performance during Upper Limb-Focused Functional Tasks.

BACKGROUND: Breast reconstruction after curative breast cancer surgery is becoming increasingly common. There is evidence to suggest that these surgeries have negative effects on shoulder function, but to date there have been no investigations of shoulder biomechanics during functional tasks in this group. The purpose of this study was to define and compare upper limb motion of patients with breast cancer who underwent mastectomy only or mastectomy with reconstruction with a control group without cancer during a range of work-related functional tasks. METHODS: Ninety-five women participated: 25 controls, 25 patients with breast cancer who received a mastectomy only, and 45 patients with breast cancer who received a mastectomy with reconstruction (implant, latissimus dorsi flap, or deep inferior epigastric artery perforator flap). Motion of the torso, humeri, and scapulae were tracked during arm-focused functional tasks, involving reaching, dexterity, and lifting overhead, and joint angles were calculated. Mean, maximum, and minimum angles were calculated and compared among groups using one-way analyses of variance ( p < 0.05). RESULTS: The reconstruction group had significantly different kinematics than the other two groups. Throughout task performance, patients who had reconstruction had increased scapular posterior tilt and increased humeral external rotation. These findings are consistent with reconstruction surgical procedures and may highlight muscle pattern alterations that interfere with co-contraction, stability, and functional task performance. CONCLUSIONS: The findings suggest that breast reconstruction surgery influences functional task performance. Scapular and humeral kinematics may indicate movement pattern differences that are important to address in rehabilitation. CLINICAL QUESTION/LEVEL OF EVIDENCE: Risk, II.

Do Musculoskeletal Disorders Affect Work Tasks in Farmers: A Study of Rural Saskatchewan.

OBJECTIVE: Musculoskeletal disorders (MSDs) are common among farmers, yet associated difficulty during work is not well understood. The purpose of this study was to determine the connection between MSDs and work-related task difficulty in rural Saskatchewan. METHODS: Rural Saskatchewan farmers and farm workers with history of MSD in the last 5 years ( n = 72) participated via an online survey. RESULTS: Shoulder MSDs were the most common (75%), followed by neck (65%), knees (61%), and lower back (58%). Many participants reported more than one MSD. Presence of MSDs leads to difficulty in work tasks; for example, difficulty when operating power tools with hands was 8.7 times more likely for those with shoulder MSD. CONCLUSIONS: MSDs in rural Saskatchewan farmers are associated with greater work task difficulty, and future research into risk factors related to those tasks can guide prevention strategies.

Evidence of rotator cuff disease after breast cancer treatment: scapular kinematics of post-mastectomy and post-reconstruction breast cancer survivors.

BACKGROUND: Breast cancer survivors may be at risk of experiencing rotator cuff disease after treatment. Biomechanical alterations following surgery potentially predispose survivors to develop this disorder. OBJECTIVE: To examine scapular kinematics in breast cancer survivors with and without impingement pain during an overhead reach task. DESIGN: A cross-sectional study. METHODS: Three surgery groups were included: non-cancer controls, mastectomy-only survivors and post-reconstruction survivors. Breast cancer survivor groups were also categorized by the presence of impingement pain. Scapular motion was tracked during an overhead reach task, performed separately by both arms. Maximum scapular internal rotation, upward rotation and tilt were calculated. Two-way analyses of variance with interactions (p < .05) were used to test the effects of group (control, mastectomy-only, reconstruction) and impingement pain (pain, no pain) on each variable within a (left/right) side. RESULTS: Scapular kinematics varied with the group by pain interaction. On the right side, the mastectomy-pain group had reduced upward rotation, while the reconstruction-pain group had higher upward rotation (mastectomy-only: 22.9° vs. reconstruction: 31.2°). On the left side, the mastectomy-pain group had higher internal rotation, while the reconstruction-pain group had reduced internal rotation (mastectomy-only: 45.1° vs. reconstruction: 39.3°). However, time since surgery was longer in the mastectomy-pain group than reconstruction-pain group, suggesting there may be a temporal component to kinematic compensations. CONCLUSIONS: There are kinematic alterations in breast cancer survivors that may promote future development of rotator cuff disease. Compensations may begin as protective and progress to more harmful alterations with time.KEY MESSAGESScapular kinematics varied with surgery and pain interaction: upward rotation was lower and internal rotation higher in mastectomy-pain group, while upward rotation was higher and internal rotation lower in reconstruction-pain group.Kinematics alterations may also be associated with time since surgery, as the mastectomy-pain group had longer time since surgery than the reconstruction-pain group.Kinematic alterations may transition from protective to harmful over time.In-depth analyses by reconstruction type are needed to determine surgery-specific effects on kinematics and their potential impact on the development of rotator cuff disease.

The utility of the acromion marker cluster (AMC) in a clinical population.

INTRODUCTION: The acromion marker cluster (AMC) is a non-invasive scapular motion tracking method. However, it lacks testing in clinical populations, where unique challenges may present. This investigation resolved the utility of the AMC approach in a compromised clinical population. METHODS: The upper body of breast cancer survivors (BCS) and controls were tracked via motion capture and scapular landmarks palpated and recorded using a digitizer at static neutral to maximum elevation postures. The AMC tracked the scapula during dynamic maximum arm abduction. Both single (SC) and double calibration (DC) methods were applied to calculate scapular angles. The influences of calibration method, elevation, and group on mean and absolute error with two-way fixed ANOVAs with interactions (p < 0.05). Root mean square errors (RMSE) were calculated and compared. RESULTS: DC improved AMC estimation of palpated scapular orientation over SC, especially at higher arm elevations; RMSE averaged 11° higher for SC than DC at maximum elevation, but the methods were only 2.2° different at 90° elevation. DC of the AMC yielded mean error values of ∼5-10°. These approximate errors reported for AMC with young, lean adults. CONCLUSIONS: The AMC with DC is a non-invasive method with acceptable error for measuring scapular motion of BCS and age-matched controls.

Activation patterns of shoulder internal and external rotators during pure axial moment generation across a postural range.

Musculoskeletal risk is mediated by body posture, especially for static tasks. Workstations that require non-neutral postures can lead to increased load, muscular fatigue and injury risk. However, demands during simple axial rotation tasks are not well-defined. The purpose of this study is to quantify the muscular activity of during static axial rotation in a range of postures. Eighteen participants performed 76 axial rotation exertions in varying combinations of humeral elevation angles (30°-60°-90°-120°-150°), plane of elevation (30°-60°-90°-120°) and exertion intensity (20-40%). Six unilateral (right) muscles (pectoralis major (clavicular and sternal), posterior deltoid, teres major, infraspinatus, latissiumus dorsi) were monitored using surface electromyography (EMG). EMG was normalized and integrated over 2 s. The influences of elevation, plane, and intensity on activity levels were then tested with a 3-way ANOVAs (p < .05). During internal rotation, activity was highest at low elevation/high plane combinations for the internal rotators, but at high elevation/low plane combinations for the external rotators. During the 40% intensity exertions, activity levels were highest at lower elevations for internal rotator but at high elevations for the external rotators. During external rotation, as the degree of elevation increased, the activity of the external rotator muscles also increased while internal rotators were unaffected. Humeral muscles responsible for axial rotation are influenced by arm posture during axial rotation exertions. High elevation and plane combinations resulted in high demands for external rotator muscles and this should be considered for job design and injury risk.

The Collagens DPY-17 and SQT-3 Direct Anterior-Posterior Migration of the Q Neuroblasts in C. elegans.

Cell adhesion molecules and their extracellular ligands control morphogenetic events such as directed cell migration. The migration of neuroblasts and neural crest cells establishes the structure of the central and peripheral nervous systems. In C. elegans, the bilateral Q neuroblasts and their descendants undergo long-range migrations with left/right asymmetry. QR and its descendants on the right migrate anteriorly, and QL and its descendants on the left migrate posteriorly, despite identical patterns of cell division, cell death, and neuronal generation. The initial direction of protrusion of the Q cells relies on the left/right asymmetric functions of the transmembrane receptors UNC-40/DCC and PTP-3/LAR in the Q cells. Here, we show that Q cell left/right asymmetry of migration is independent of the GPA-16/Ga pathway which regulates other left/right asymmetries, including nervous system L/R asymmetry. No extracellular cue has been identified that guides initial Q anterior versus posterior migrations. We show that collagens DPY-17 and SQT-3 control initial Q direction of protrusion. Genetic interactions with UNC-40/DCC and PTP-3/LAR suggest that DPY-17 and SQT-3 drive posterior migration and might act with both receptors or in a parallel pathway. Analysis of mutants in other collagens and extracellular matrix components indicated that general perturbation of collagens and the extracellular matrix (ECM) did not result in directional defects, and that the effect of DPY-17 and SQT-3 on Q direction is specific. DPY-17 and SQT-3 are components of the cuticle, but a role in the basement membrane cannot be excluded. Possibly, DPY-17 and SQT-3 are part of a pattern in the cuticle and/or basement membrane that is oriented to the anterior-posterior axis of the animal and that is deciphered by the Q cells in a left-right asymmetric fashion. Alternatively, DPY-17 and SQT-3 might be involved in the production or stabilization of a guidance cue that directs Q migrations. In any case, these results describe a novel role for the DPY-17 and SQT-3 collagens in directing posterior Q neuroblast migration.

A randomized controlled trial investigating effects of an individualized pedometer driven walking program on chronic low back pain.

BACKGROUND: Walking is an easily prescribed physical activity for people with low back pain (LBP). However, the evidence for its effectiveness to improve pain and disability levels for people with chronic low back pain (CLBP) within a community setting has not been evaluated. This study evaluates the effectiveness of a clinician guided, pedometer-driven, walking intervention for increasing physical activity and improving clinical outcomes compared to education and advice. METHODS: Randomized controlled trial recruiting N = 174 adults with CLBP. Participants were randomly allocated into either a standardized care group (SG) or pedometer based walking group (WG) using minimization allocation with a 2:1 ratio to the WG. Prior to randomization all participants were given a standard package of education and advice regarding self-management and the benefits of staying active. Following randomization the WG undertook a physiotherapist guided pedometer-driven walking program for 12 weeks. This was individually tailored by weekly negotiation of daily step targets. Main outcome was the Oswestry Disability Index (ODI) recorded at baseline, 12 weeks, 6 and 12 months. Other outcomes included, numeric pain rating, International Physical Activity Questionnaire (IPAQ), Fear-Avoidance Beliefs Questionnaire (FABQ), Back Beliefs questionnaire (BBQ), Physical Activity Self-efficacy Scale, and EQ-5D-5L quality of life estimate. RESULTS: N = 138 (79%) participants completed all outcome measures at 12 weeks reducing to N = 96 (55%) at 12 months. Both observed and intention to treat analysis did not show any statistically significant difference in ODI change score between the WG and the SG at all post-intervention time points. There were also no significant between group differences for change scores in all secondary outcome measures. Post hoc sensitivity analyses revealed moderately disabled participants (baseline ODI ≥ 21.0) demonstrated a greater reduction in mean ODI scores at 12 months in the WG compared to SG, while WG participants with a daily baseline step count < 7500 steps demonstrated a greater reduction in mean ODI scores at 12 weeks. CONCLUSIONS: Overall, we found no significant difference in change of levels of (ODI) disability between the SG and WG following the walking intervention. However, ODI responses to a walking program for those with moderate levels of baseline disability and those with low baseline step count offer a potential future focus for continued research into the benefit of walking as a management strategy for chronic LBP. TRIAL REGISTRATION: United States National Institutes of Health Clinical Trails registry (http://ClinicalTrials.gov/) No. NCT02284958 (27/10/2014).

Examining assessment methods of scapular motion: Comparing results from planar elevations and functional task performance.

BACKGROUND: Scapular kinematics of breast cancer survivors are most often evaluated during arm elevation. However, known compensations exist during functional task performance. The purpose of this study was to determine if scapular kinematics of breast cancer survivors during arm elevation are related to scapular kinematics during functional task performance. METHODS: Scapular kinematics of 25 non-cancer controls and 25 breast cancer survivors (split by presence of impingement pain) during arm elevation in 3 planes and 3 reaching and lifting functional tasks were measured. Scapular upward rotation and scapulohumeral rhythm (SHR) at 30° increments of arm elevation were calculated. Between-group differences of upward rotation during arm elevation were evaluated with one-way ANOVAs (p < 0.05). The association of upward rotation angle and SHR during arm elevation and functional tasks was tested with Pearson correlations (p < 0.05). FINDINGS: Scapular upward rotation was reduced for the breast cancer survivor with pain at lower levels of arm elevation in each plane by up to 7.1° (p = .014 to 0.049). This is inconsistent with functional task results, in which upward rotation decrements occurred at higher levels of arm elevation. Upward rotation angles and SHR during arm elevation had an overall weak-to-moderate relationship (r = 0.003 to 0.970, p = .001 to 0.048) to values from functional tasks. Arm elevation during sagittal plane elevation demonstrated scapular upward rotation that was most closely associated to upward rotation during functional task performance. INTERPRETATION: Inconsistent relationships suggests that clinical evaluations should adopt basic functional movements for scapular motion assessment to complement simple arm elevations.

Estimating Muscle Forces for Breast Cancer Survivors During Functional Tasks.

Breast cancer survivors have known scapular kinematic alterations that may be related to the development of secondary morbidities. A measure of muscle activation would help understand the mechanisms behind potential harmful kinematics. The purpose of this study was to define muscle force strategies in breast cancer survivors. Shoulder muscle forces during 6 functional tasks were predicted for 25 breast cancer survivors (divided by impingement pain) and 25 controls using a modified Shoulder Loading Analysis Module. Maximum forces for each muscle were calculated, and 1-way analysis of variance (P < .05) was used to identify group differences. The differences between maximum predicted forces and maximum electromyography were compared with repeated-measures analysis of variance (P < .05) to evaluate the success of the model predictions. Average differences between force predictions and electromyography ranged from 7.3% to 31.6% but were within the range of previously accepted differences. Impingement related pain in breast cancer survivors is associated with increased force of select shoulder muscles. Both pectoralis major heads, upper trapezius, and supraspinatus peak forces were higher in the pain group across all tasks. These force prediction differences are also associated with potentially harmful kinematic strategies, providing a direction for possible rehabilitation strategies.

Impingement pain affects kinematics of breast cancer survivors in work-related functional tasks.

BACKGROUND: Breast cancer survivors may encounter upper limb morbidities post-surgery. It is currently unclear how these impairments affect arm kinematics, particularly during functional task performance. This investigation examined upper body kinematics during functional tasks for breast cancer survivors and an age-matched control group. METHODS: Fifty women (aged 35-65) participated: 25 breast cancer survivors who had undergone mastectomy and 25 age-range matched controls. Following basic clinical evaluation, including shoulder impingement tests, motion of the torso and upper limbs were tracked during six upper limb-focused functional tasks from which torso, scapular, and thoracohumeral angles were calculated. Between-group differences were evaluated with independent t-tests (p < .05). The breast cancer group was then divided based upon impingement tests and differences between the three new groups were tested with one-way ANOVAs (p < .05). FINDINGS: Breast cancer survivors had higher disability scores, lower range of motion, and lower performance scores. The largest kinematic differences existed between the breast cancer survivors with impingement pain and the two non-pain groups. During overhead tasks, right peak scapular upward rotation was significantly reduced (d = 0.80-1.11) in the breast cancer survivors with impingement pain. This group also demonstrated trends of decreased peak humeral abduction and internal rotation at extreme postures (d = 0.54-0.78). These alterations are consistent with kinematics considered high risk for rotator cuff injury development. INTERPRETATION: Impingement pain in breast cancer survivors influences functional task performance and may be more important to consider than self-reported disability when evaluating pain and potential injury development.

Workstation configuration and container type influence upper limb posture in grocery bagging.

INTRODUCTION: Repetitive movements and awkward postures are two persistent injury risk factors for grocery store cashiers. Due to the recent rise in popularity of environmentally-friendly grocery bagging options, current recommendations for cashiers are likely outdated. Correspondingly, the objective of this study was to examine the effects of cashier-specific work demands, workstation configuration, and container type on upper limb postures during typical job activities. METHODS: Fifteen experienced cashiers bagged groceries at varying combinations of workstation height (low, medium, high) and container type (reusable bins, reusable bags, plastic bags). Upper limb movement was quantified with motion capture and amplitude probability distribution functions of humeral elevation and humeral axial internal rotation were used to assess the static (10th percentile), median (50th percentile), and peak (90th percentile) postural demands, which were then interpreted in the context of existing postural guidelines. RESULTS: High workstation height and reusable bags increased right arm elevation at peak posture by 15.7° compared to the low workstation height and reusable bin combination. However, reusable bins increased internal rotation demands of the right arm by 4.3° compared to other container types. Left arm elevation and internal rotation were consistently lower than right arm angles. CONCLUSION: Cashiers are encouraged to adjust the workstation to decrease the arm elevation and internal rotation required by higher workstation heights and tall containers, and to use both arms for scanning and packing, when possible, to reduce undesirable arm postures.

The combined fatigue effects of sequential exposure to seated whole body vibration and physical, mental, or concurrent work demands.

Many occupations in agriculture, construction, transportation, and forestry are non-routine, involving non-cyclical tasks, both discretionary and non-discretionary work breaks, and a mix of work activities. Workers in these industries are exposed to seated whole body vibration (WBV) and tasks consisting of physical, mental, or a combination of demands. Risk assessment tools for non-routinized jobs have emerged but there remains a need to understand the combined effects of different work demands to improve risk assessment methods and ultimately inform ergonomists and workers on optimum work arrangement and scheduling strategies. The objective of this study was to investigate fatigue-related human responses of WBV sequentially combined with physical, mental, or concurrent physical and mental demands. Sixteen healthy participants performed four conditions on four separate days: (1) physically demanding work, (2) mentally demanding work, (3) concurrent work, and (4) control quiet sitting. For each condition, participants performed two 15-minute bouts of the experimental task, separated by 30-minutes of simulated WBV based on realistic all-terrain vehicle (ATV) riding data. A test battery of fatigue measures consisting of biomechanical, physiological, cognitive, and sensorimotor measurements were collected at four interval periods: pre-session, after the first bout of the experimental task and before WBV, after WBV and before the second bout of the experimental task, and post-session. Nine measures demonstrated statistically significant time effects during the control condition; 11, 7, and 12 measures were significant in the physical, mental, and concurrent conditions, respectively. Overall, the effects of seated WBV in combination with different tasks are not additive but possibly synergistic or antagonistic. There appears to be a beneficial effect of seated ATV operation as a means of increasing task variation; but since excessive WBV may independently pose a health risk in the longer-term, these beneficial results may not be sensible as a long-term solution.