Amplitude Probability Distribution Function Research Articles

핸드폰 사용이 목과 어깨 근육의 근육활성도와 피로도에 미치는 영향

The smart-phone has become a necessity for most people. In this study, we determined that using a smart-phone for 20 minutes can cause increased neck and shoulder muscle activities and fatigue. Seventeen healthy male smart-phone users who attended Yonsei University played a smart-phone game for 20 minutes and changes in their bilateral cervical erector spinae and upper trapezius muscle activities and fatigue were measured. To assess muscle activities and fatigue, we used the following variables: the median frequency, the 50th percentile Amplitude probability distribution function (APDF) value (median load), and the discrepancy in the 90th percentile APDF value and the 10th percentile APDF value (APDF range). A paired t-test was used to compare pre-smart-phone-use status with post-smart-phone-use-status. The median frequency of the bilateral cervical erector spinae and the upper trapezius decreased significantly after 20 minutes of smart-phone use (p.05). These findings suggest that using smart-phones for 20 minutes can induce muscle fatigue and increased neck and shoulder muscle activities.

Variation in Muscle Activity Among Office Workers When Using Different Information Technologies at Work and Away From Work

To determine differences in muscle activity amplitudes and variation of amplitudes when using different information and communication technologies (ICT). Office workers use different ICT to perform tasks. Upper body musculoskeletal complaints are frequently reported by this occupational group. Increased muscle activity and insufficient variation are potential risk factors for musculoskeletal complaints. Muscle activity of right and left upper trapezius and right wrist extensor muscle bundle (extensor carpi radialis longus and brevis) of 24 office workers (performing their usual tasks requiring different ICT at work and away from work) were measured continuously over 10 to 12 hours. Muscle activity variation was quantified using two indices, amplitude probability distribution function and exposure variation analysis. There was a trend for electronics-based New ICT tasks to involve less electromyography (EMG) variation than paper-based Old ICT tasks. Performing Combined ICT tasks (i.e., using paper- and electronics-based ICT simultaneously) resulted in the highest muscle activity levels and least variation; however, these Combined ICT tasks were rarely performed. Tasks involving no ICT (Non-ICT) had the greatest muscle activity variation. Office workers in this study used various ICT during tasks at work and away from work. The high EMG amplitudes and low variation observed when using Combined ICT may present the greatest risk for musculoskeletal complaints, and use of Combined ICT by workers should be kept low in office work. Breaking up combined, New, and Old ICT tasks, for example, by interspersing highly variable Non-ICT tasks into office workers' daily tasks, could increase overall muscle activity variation and reduce risk for musculoskeletal complaints.

극장식 계단강의실 의자와 일반강의실 의자에서 받아쓰기 과제 수행 시 등세모근육의 근 활성도 비교

The purpose of this study was to investigate the effect of the two different types of chairs on trapezius muscle activation during dictation tasks. Seventeen university students, each of whom were within <TEX>${\pm}1$</TEX> standard deviation of the mean Korean standard body size, voluntarily participated in this study. Surface electromyography was used to collect electrical signals from both the upper and lower trapezius muscles. Amplitude Probability Distribution Function (APDF) was performed to analyze the muscle activity. The findings of this study were 1) The backrest-point height of the auditorium chair and the height, length and width of the connected desk were shorter than what was suggested by the KS. Another difference was that the auditorium chair had a bigger angle of the backrest compared to the classroom chair. 2) Regarding within-subject effect the sole statistically significant difference was found between activation of the upper trapezius muscle. The upper trapezius muscle's %RVC in the APDF 10th-50th-90th percentile was statistically higher for participants sitting in the auditorium chair than for participants sitting in the classroom chair (p<.05). 3) There was an interaction effect between the 'two chair-types' and the 'two muscle-sides' in the APDF 10th-50th percentile (p<.05). 4) There was an interaction effect between the 'two chair-types' and the 'three gaze-direction' in the APDF 90th percentile (p<.05). The findings of this study indicated that maintaining a writing posture for a prolonged period of time in an auditorium chair significantly increased the left upper trapezius muscle activation compared to a classroom chair.

Multivariate, longitudinal analysis of the impact of changes in office work environments on surface electromyography measures

To detect impacts of changes in work environment and worker-equipment interface variables upon surface electromyography (EMG) measures using multivariate, longitudinal analysis. For 33 office workers, yearly measurements (1999-2001) were taken during normal work. Independent variables were related to work environment (expert-observed equipment dimensions, work organization on questionnaire) and interface (expert-observed postures, self-reported workstation-equipment relative fit i.e. inside or outside guidelines-informed location, and 30 min video-based task analysis). Internal mechanical exposure (EMG) was recorded bilaterally from extensor carpi radialis brevis (ECRB) and upper trapezius sites, each side, also for 30 min. Dependent variables were amplitude probability distribution functions (APDF 50 and 90%) and gaptime for entire record EMG (over all tasks) and task-specific EMG (for four separate tasks). Multivariate mixed models used independent variables to predict EMG measures (4 muscle sites × (1 entire record + 4 task specific) = 20 models total). Among EMG measures, 9/16 means and 2/16 variances were significantly different across years (p < 0.1). Environment and interface variables explained part of the variation in EMG measures in 13/20 models. The most consistent predictors included: (1) increased monitor distance predicted reduced APDFs and increased gaptimes; (2) wrist extension <20° predicted decreases in left ECRB APDFs; (3) keyboard location within guidelines predicted improvements in all right ECRB EMG measures during keyboarding; and (4) longer task duration predicted higher APDFs and lower gaptimes. Longitudinal analysis with multivariate models can detect the impacts of changes in environment and interface exposures on EMG measures among office workers.

Observation of Blobs and Holes in the Boundary Plasma of EAST Tokamak

Intermittent convective transport at the edge and in the scrape-off layer (SOL) of EAST was investigated by using fast reciprocating Langmuir probe. Holes, as part of plasma structures, were detected for the first time inside the shear layer. The amplitude probability distribution function of the turbulence is strongly skewed, with positive skewed events (“blobs") prevailing in the SOL region and negative skewed events (“holes") dominant inside the shear layer. The statistical properties coincide with previous observations from JET. The generation mechanism of blobs and holes is also discussed. In addition burst structure and dynamics character of them are also presented.

Modeling of plasma turbulence and transport in the Large Plasma Device

Numerical simulation of plasma turbulence in the Large Plasma Device (LAPD) [W. Gekelman, H. Pfister, Z. Lucky et al., Rev. Sci. Instrum. 62, 2875 (1991)] is presented. The model, implemented in the BOUndary Turbulence code [M. Umansky, X. Xu, B. Dudson et al., Contrib. Plasma Phys. 180, 887 (2009)], includes three-dimensional (3D) collisional fluid equations for plasma density, electron parallel momentum, and current continuity, and also includes the effects of ion-neutral collisions. In nonlinear simulations using measured LAPD density profiles but assuming constant temperature profile for simplicity, self-consistent evolution of instabilities and nonlinearly generated zonal flows results in a saturated turbulent state. Comparisons of these simulations with measurements in LAPD plasmas reveal good qualitative and reasonable quantitative agreement, in particular in frequency spectrum, spatial correlation, and amplitude probability distribution function of density fluctuations. For comparison with LAPD measurements, the plasma density profile in simulations is maintained either by direct azimuthal averaging on each time step, or by adding particle source/sink function. The inferred source/sink values are consistent with the estimated ionization source and parallel losses in LAPD. These simulations lay the groundwork for more a comprehensive effort to test fluid turbulence simulation against LAPD data.

Examining the low, high and range measures of muscle activity amplitudes in symptomatic and asymptomatic computer users performing typing and mousing tasks

Past studies on work-related musculoskeletal disorders (WMSD) have reported increased median muscle activities in terms of 50th% of amplitude probability distribution function (APDF), and this was thought to be a manifestation of altered motor control--an important mechanism contributing to WMSD. The present study aimed to examine whether such altered motor control was also present in other parameters of APDF--the 10th and 90th% values, which can be considered indicators of the low and high measures of muscle activity. The difference between 10th and 90th% APDF can be considered an indicator of the variation in muscle activity amplitude (the "APDF range"). Surface electromyography was examined in female office workers as Case (n = 21) and Control (n = 18) subjects. The APDF variables were measured in cervical erector spinae (CES) and upper trapezius (UT) muscles during typing, mousing and type-and-mouse, for 20 min each. The Case Group had significantly higher CES activity in the 10th, 90th% and APDF range compared to Controls. The UT muscles showed similar trends but the between-group differences were not statistically significant. These results have demonstrated the robustness of the APDF variables as sensitive indicators of motor control variations in symptomatic subjects with musculoskeletal disorders.

Statistical analysis of the turbulent Reynolds stress and its link to the shear flow generation in a cylindrical laboratory plasma device

The statistical properties of the turbulent Reynolds stress arising from collisional drift turbulence in a magnetized plasma column are studied and a physical picture of turbulent driven shear flow generation is discussed. The Reynolds stress peaks near the maximal density gradient region, and is governed by the turbulence amplitude and cross-phase between the turbulent radial and azimuthal velocity fields. The amplitude probability distribution function (PDF) of the turbulent Reynolds stress is non-Gaussian and positively skewed at the density gradient maximum. The turbulent ion-saturation (Isat) current PDF shows that the region where the bursty Isat events are born coincides with the positively skewed non-Gaussian Reynolds stress PDF, which suggests that the bursts of particle transport appear to be associated with bursts of momentum transport as well. At the shear layer the density fluctuation radial correlation length has a strong minimum (∼4–6mm∼0.5Cs∕Ωci, where Cs is the ion acoustic speed and Ωci is the ion gyrofrequency), while the azimuthal turbulence correlation length is nearly constant across the shear layer. The results link the behavior of the Reynolds stress, its statistical properties, generation of bursty radially going azimuthal momentum transport events, and the formation of the large-scale shear layer.

Cross-sectional Study of Upper Trapezius Muscle Activity and Self-Reported Neck/Shoulder Pain

The purpose of this cross-sectional study was to compare the observed associations between upper trapezius muscle activity, as estimated with several summary measures obtained from surface electromyography (EMG), and self-reported neck/shoulder pain among a sample of 231 manufacturing workers. EMG methods used in this study included mean root-mean-square amplitude, the amplitude probability distribution function (APDF), EMG gaps analysis, and clustered exposure variation analysis. The observed seven-day prevalence of neck/shoulder pain was 13.9%. Of the EMG summary measures, only the 90 th percentile of the APDF was significantly associated with symptoms, with crude and adjusted odds ratios of 2.57 (1.02–6.49) and 2.78 (1.07–7.21) per natural log unit, respectively. This study was largely inconclusive due to the similarity in the distributions of the summary measures between symptomatic and non-symptomatic participants, and explicit measures of posture and repetition may produce stronger associations with symptoms.

Ergonomic analysis of postural and muscular loads to diagnostic sonographers

Musculoskeletal disorders are prevalent in diagnostic sonographers. This study quantifies the postural and muscular loads during ultrasound scanning. Video-based stop-motion postural analysis at 4 samples/minute for 24 full scans (527.5 minutes) by 11 sonographers showed sonographers spend 68% of scanning time with >30 o shoulder abduction, 63% with >30 o shoulder outward rotation, and 37% with the neck bent forward, laterally or twisted >20 o. The shoulder was observed to be unsupported, or static, for 73% of scanning time and this was significantly higher for carotid scans compared with abdominal, obstetrical or leg scans ( p<0.05). Electromyography (EMG) was collected for seven scans performed by three sonographers on three shoulder muscles: Supraspinatus, infraspinatus, and trapezius; as well as for flexor carpi ulnaris. Static (0.10) amplitude probability distribution functions (APDFs) for all three shoulder muscles exceeded 3% MVC corresponding to a “medium” risk rating for shoulder–neck disorders. Mean forearm flexor EMG was 3.96 kg (SD 2.94), with occasional peak forces as high as 27.6 kg. Relevance to industry Diagnostic sonographers experience long durations in static shoulder abduction and outward rotation, with high peak and sustained grip forces. These risk factors are consistent with the high prevalence of neck and upper limb musculoskeletal disorders and symptoms reported by many sonographers.

Evaluation of Distal Upper Extremity Musculoskeletal Load During Routine Colonoscopy

Background: Physicians who perform endoscopies are at increased risk for developing recurrent thumb, hand, elbow and low back pain. Musculoskeletal disorders of the upper extremities are related to repeated, forceful movements of the hands and arms. As the demand for colonoscopy increases, so will the physical loads on the hands and arms of endoscopists. The risk factors of upper extremity overuse injuries during routine endoscopy, such as applied pinch force and muscle loads, have not been evaluated during routine endoscopy. We performed a pilot study to determine right thumb pinch force and hand and wrist muscle activities during colonoscopy. Methods: Three gastroenterologists were studied while each performed three colonoscopies. Electromyographic (EMG) activity of the right and left forearm extensor carpi radialis (ECR), right and left flexor digitorum superficialis (FDR), and left abductor pollicis longus (APL) was measured with surface electrodes. Summary measures of EMG data were calculated using the amplitude probability distribution function (APDF), which is a method to quantify muscular activity by normalizing it to maximum voluntary contraction (MVC). Prior studies have shown median levels of muscle activity (APDF 50%tile) of >7-20% MVC and low levels of muscle activity (APDF 10%ile) of >2-5% MVC are associated with increased risk of injury. Right thumb pinch force was measured using a thin profile, custom designed pressure sensor. Prior studies have shown peak pinch force levels (APDF 90%tile) of >10N are associated with an increased risk of injury. Results: The mean peak pinch force across the 9 patients (APDF 90) was 8.6N (SD ± 2.1). The highest pinch forces occurred during insertion: APDF 90 = 10.4N in the left colon and APDF 90 = 10.1N in the right colon. The highest muscle activities were observed in the left ECR (APDF 10 = 10% MVC and APDF 50 = 20% MVC). Left ECR activity was greatest during insertion into the left colon (APDF 10 = 9.0%, APDF 50 = 25.1%) and right colon (APDF 10 = 11.4%, APDF 50 = 23.9%). APDF 10 values of the other muscle groups studied did not exceed 5% of MVC, and APDF 50 values did not exceed 20% of MVC. Conclusions: Based on this pilot data, colonoscopy is associated with a borderline risk of musculoskeletal disorders of the upper extremities, specifically right thumb and left wrist extensor injury. Repeated, high thumb pinch forces can lead to DeQuervain's tendinitis and carpal tunnel syndrome. Repeated, high left ECR muscle loads can lead to second and third extensor compartment tenosynovitis at the wrist and epicondylitis. Further study is needed to identify modifiable risk factors and evaluate methods to reduce this risk.

Polynomial chaos expansions for travel time and amplitude uncertainty in acoustic time series in ocean waveguides

Polynomial chaos (PC) techniques have shown themselves to be a powerful technique for the estimation of the statistical properties of ocean acoustic propagation for situations where the vertical and horizontal structure of sound speed uncertainty can be specified in terms of empirical orthogonal functions (EOFs) with known amplitude probability distribution functions. Here we extend the CW solutions for the statistical properties of the normal models describing the acoustic field in the presence of internal waves with Gaussian distributed EOF descriptions to the time domain to describe the scintillation of the acoustic time series. Results are compared to exact solutions as well as to estimates based on the adiabatic approximation. Results show that the PC solutions do a much better job of capturing the true variability of the exact solutions for the time series variability than the adiabatic approximations does. [Work supported by ONR.]

Quantifying precision and speed effects on muscle loading and rest in an occupational hand transfer task

Musculoskeletal disorders of the upper limb are common among semi-automated occupational hand transfer tasks. Ten healthy adults were recruited (five males, five females). Surface electromyography (EMG) was collected from eight muscles of the right arm: Upper trapezius, supraspinatus, infraspinatus, brachioradialis, extensor carpi radialis, extensor carpi ulnaris, extensor digitorum indicis, and flexor digitorum superficialis. The task consisted of a repetitive transfer of a 1.8-kg part at 2, 3, and 5 s cycle times (CTs), using power and chuck grips, and under precision and non-precision conditions. EMG was quantified using the amplitude probability distribution function (muscle loading) and gaps analyses (muscle rest). For all muscles, static (tenth percentile APDF) loading exceeded 1% and the muscle rest from gaps was below 10% at 2 and 3 s CT. Precision increased loading in forearm muscles, and increased perceived difficulty ( p<0.001). The findings suggest that precision increased the loading by about 43% in the distal musculature under the conditions tested. Relevance to industry This study will be useful in modeling lower risk CT and designing precision jobs (e.g. hand transfer) in semi-automated industries. Muscle loading and rest as physiologic parameters are influenced differently by CT, grip type and precision requirements of a task.

The effects of lumbar massage on muscle fatigue, muscle oxygenation, low back discomfort, and driver performance during prolonged driving

An increasing dependence of society on automobiles for both work and leisure and the corresponding increase in time spent seated in the car has been correlated with a greater risk of low back pain and absence from work (Porter and Gyi 2002). This study examined the effects of three types of lumbar massage units on seating comfort, muscle fatigue, muscle oxygenation, muscle blood flow and driving performance during a 1 h simulated driving task. Electromyographic (EMG) signals were recorded from the right and left thoracic and lumbar erector spinae musculature. Average EMG (AEMG), mean power frequency (MPF), gaps and amplitude probability distribution function (APDF) parameters were analysed from the three massage seats and compared to a control seat. Near infrared spectroscopy (NIRS) and skin temperature from the right thoracic and lumbar erector spinae were used as an indication of muscle oxygenation and blood flow throughout the driving task. Ratings of perceived discomfort were used to assess driver discomfort, and driving performance was assessed by calculating mean lap times for the duration of each driving trial. The results showed statistically significant increases in skin temperature compared with the control seat after 60 min of driving. The NIRS results reflected these trends although the results were not statistically significant. AEMG and MPF measures showed no significant differences between the seats. MPF measures were found to increase over time, effects attributed to increases in muscle temperature. Gaps and APDF analyses revealed greater rest times and lower activation levels, respectively, with the control seat, which could result in increased loading of passive structures. This study demonstrated the beneficial effects of lumbar massage systems in increasing muscle blood flow and oxygenation. Although EMG parameters were not significantly different, the trends support the significant blood flow results. Future research should include longer driving times and adjustments in EMG measures to account for the effects of increasing muscle temperature on AEMG and MPF measures.

Intermittent turbulence and turbulent structures in a linear magnetized plasma

Strongly intermittent turbulence is observed in the shadow of a limiter in the large plasma device at UCLA [W. Gekelman et al., Rev. Sci. Instrum. 62, 2875 (1991)]. The amplitude probability distribution function of the turbulence is strongly skewed, with density depletion events (or “holes”) dominant in the high-density region and density-enhancement events (or “blobs”) dominant in the low-density region. Two-dimensional cross-conditional averaging shows that the blobs are detached, outward-propagating filamentary structures with a clear dipolar potential, while the holes appear to be part of a more extended turbulent structure. A statistical study of the blobs reveals a typical size of ten times the ion sound gyroradius and a typical velocity of one-tenth the sound speed.

Evaluation of Shoulder Muscular Fatigue Induced during Mouse Operation in a VDT Task

This study was designed to evaluate localized muscular fatigue induced during mouse operation in a VDT task. Ten male undergraduates from 19 to 23 years old participated in the experiment. The subject performed a pointing task with a PC mouse for about 4 hours. The EMG measurements and psychological rating of fatigue were conducted before the experimental task and after each 30-minutes block during the experimental task. The changes in the Mean Power Frequency (MPF) and Percentage Maximum Voluntary Contraction (%MVC)-shift for the constant cumulative probability in the Amplitude Probability Distribution Function (APDF) with time were explored. The correspondence between the index (MPF or APDF) and the subjective rating of localized muscular fatigue was also examined. The performance was nearly constant across all blocks. The psychological rating of fatigue tended to increase with time. The MPF tended to increase with time, although the main effect of block (time) was not statistically significant. The %MVC-shift tended to increase with time. The correspondence with the perceived sensation of localized muscular fatigue was higher when using the %MVC-shift than when using the MPF. Based on the results, the effectiveness of the indexes used for evaluating localized muscular fatigue was discussed. The %MVC-shift obtained from the APDF was found to be a sensitive index of localized muscular fatigue and corresponded well with the subjective rating of localized muscular fatigue.

The effect of sampling frequency on EMG measures of occupational mechanical exposure

The purpose of the present study was to determine how much it is possible to downsample EMG without loosing the accuracy of some EMG measures of occupational mechanical exposure frequently used in the literature. The EMG signals of four muscles (two trapezius, right deltoid and right extensor digitorum) were collected (sampling frequency: 1024 Hz) from 20 subjects while performing a 20 min computer work task. The EMG RMS amplitude was computed from 0.125 s successive time-windows for the original (1024 Hz) and four additional digitally resampled (at 512, 256, 128 and 64 Hz) EMG signals. Three of the most frequently used data reduction methods (1. gaps analysis, 2. amplitude probability distribution function and 3. exposure variation analysis) were used to summarise the 20 min EMG activation profiles. The results from the exposure variation analysis were summarized into three variables using a new method detailed here. In general, the ANOVA for repeated measures demonstrated that a decrease of the sampling frequency significantly changed the EMG measures (relative to the 1024 Hz sampling condition) most of the time at 64 and 128 Hz, occasionally at 256 Hz, but practically never at 512 Hz. An analysis of the maximal errors (relative to the 1024 Hz condition) across all subjects supported these findings. Consequently, it was concluded that 512 Hz is quite conservative and should practically never lead to invalid EMG parameters estimations. Conversely, 256 Hz represents the lowest limit tolerable for some EMG parameters (gaps analysis, amplitude probability distribution function) while it is unacceptable for others (modified exposure variation analysis).

A Versatile Program for the Analysis of Electromyographic Data

Ergonomists and researchers often utilize electromyographic (EMG) recordings to produce estimates of muscular work load in occupational exposure assessment. Prolonged measurements, possible with recent technological advances in portable data acquisition and compact memory storage technologies, require efficient data reduction methods not always available in commercial software packages. The Iowa EMG Analysis Program (IEAP) was created to provide researchers the means to incorporate multiple processing techniques suited for the analysis of prolonged EMG measurements. IEAP currently includes subroutines to calculate the amplitude probability distribution function, exposure variation analysis, clustered exposure variation analysis, and gaps analysis profiles for up to four channels of root-mean-square processed EMG data. Data management functions include the creation of customized hypertext markup language (HTML) documentation and text files able to seamlessly incorporate analysis results into existing statistical software packages. IEAP is a powerful EMG analysis tool ideally suited for ergonomists and researchers involved in occupational ergonomics studies.

Effect of Computer Keyboard Slope on Wrist Position and Forearm Electromyography of Typists Without Musculoskeletal Disorders

Positioning a computer keyboard with a downward slope reduces wrist extension needed to use the keyboard and has been shown to decrease pressure in the carpal tunnel. However, whether a downward slope of the keyboard reduces electromyographic (EMG) activity of the forearm muscles, in particular the wrist extensors, is not known. Sixteen experienced typists participated in this study and typed on a conventional keyboard that was placed on slopes at angles of 7.5, 0, -7.5, and -15 degrees. Electromyographic activity of the extensor carpi ulnaris (ECU), flexor carpi ulnaris (FCU), and flexor carpi radialis (FCR) muscles was measured with surface electrodes, while the extension and ulnar deviation angles of the right and left wrists were measured with electrogoniometers. Wrist extension angle decreased from approximately 12 degrees of extension while typing on a keyboard with a 7.5-degree slope to 3 degrees of flexion with the keyboard at a slope of -15 degrees. Although the differences were in the range of 1% to 3% of maximum voluntary contraction (MVC), amplitude probability distribution function (APDF) of root-mean-square EMG data points from the ECU, FCU, and FCR muscles varied across keyboard slopes. Wrist extension decreased as the keyboard slope decreased. Furthermore, a slight decrease in percentage of MVC of the ECU muscle was noted as the keyboard slope decreased. Based on biomechanical modeling and published work on carpal tunnel pressure, both of these findings appear to be positive with respect to comfort and fatigue, but the exact consequences of these findings on the reduction or prevention of injuries have yet to be determined. The results may aid physical therapists and ergonomists in their evaluations of computer keyboard workstations and in making recommendations for interventions with regard to keyboard slope angle.

Trunk posture:: reliability, accuracy, and risk estimates for low back pain from a video based assessment method

It has been recently reported that both dynamic movement characteristics, as well as the duration of postures adopted during work, are important in the development of low back pain (LBP). This paper presents a video-based posture assessment method capable of measuring trunk angles and angular velocities in industrial workplaces. The inter-observer reliability, system accuracy, and the relationship of the measured exposures to the reporting of low back pain are reported. The video analysis workstation consisted of a desktop computer equipped with digital video capture and playback technology, a VCR, and a computer game type joystick. The operator could then use a joystick to track trunk flexion and lateral bending during computer-controlled video playback. The joystick buttons were used for binary input of twisting. The inter-observer reliability for peak flexion and percentage of time spent in posture category variables were excellent (ICC>0.8). Lower reliability levels were observed for peak and average velocity and movement related variables. The video analysis system time series data showed very high correlation to the criterion optoelectronic imaging system ( r=0.92). Root mean square errors averaged 5.8° for the amplitude probability distribution function data. Trunk flexion variables including peak level, peak velocity, average velocity indicators, and percent time in flexion category indicators all showed significant differences between cases and controls in the epidemiological study. A model consisting of the measures peak trunk flexion, percent time in lateral bend and average lateral bending velocity emerged after multivariable analysis for relationship to low back pain. Relevance to industry Risk of injury for the low back is multifactorial. The trunk position and movement velocity are emerging as important parameters. This analysis confirms the importance of these factors and demonstrates the utility of a video-based method to measure them in industrial settings.