Chris L. Zimmermann

Effects of seated posture on erector spinae EMG activity during whole body vibration.

The purpose of this study was to evaluate the electromyographic (EMG) response of the erector spinae to whole body vibration in three different unsupported seated postures: neutral upright, forward lean, and posterior lean. Subjects were 11 healthy college-age men. EMG was collected using bipolar surface electrodes placed bilaterally over the erector spinae at the L4 level. A modified chair with attached accelerometer was affixed to an induction type vibrator. Subjects were vibrated vertically at 4.5 Hz and 6.21 m.s-2 RMS. Data were collected in each of the three postures for 30 s pre- and post-vibration and for 2 min during vibration. Mean EMG values were determined for each sampling period and compared using ANOVA. The mean value for anterior lean was significantly larger (p < 0.05) than that for posterior lean and neutral. EMG data analysed by triggered averaging showed a phase-dependent response to the vibratory cycle for the forward leaning and neutral upright postures. The results of this study indicate that the magnitude of the vibration synchronous response of the erector spinae musculature is dependent upon body posture. This response may be an important factor in the onset of muscular fatigue and the increased incidence of back disorders among individuals exposed to whole body vibration.

Work-related musculoskeletal symptoms among construction workers in the pipe trades

Workers in the construction trades experience high rates of injuries and illnesses, including work-related musculoskeletal disorders. As the basis for formulating and implementing ergonomic changes to reduce musculoskeletal disorders among workers in the pipe trades, a cross-sectional survey was conducted. The survey instrument assessed the prevalence of work-related musculoskeletal symptoms and identified job factors that may contribute to those symptoms. A two-page questionnaire was mailed out to members of three plumber and pipe/steamfitter unions. Results from 526 (40% response rate) apprentices and journeymen indicated that the highest work-related symptoms and reported lost work time due to those symptoms, were in the back, neck, and knees. Awkward postures and working in the same position for long periods were identified as the leading causes of work-related musculoskeletal symptoms. These results can be used to formulate appropriate intervention strategies for the reduction of musculoskeletal symptoms for construction workers in the pipe trades.

Electromyographic Analysis of a Repetitive Hand Gripping Task.

Electromyography (EMG) has been proposed as a method for determining muscle effort in repetitive upper limb tasks, which are often related to cumulative trauma disorders. EMG activity of the finger flexor musculature was investigated during a repetitive hand gripping task having 5 different cycle durations (2 to 6 s), various percentage of work time (and rest) within the work cycle (20% to 80%), and 3 different grip force levels. Thirty healthy adult participants each performed 27 randomly ordered 30-s repetitive hand gripping trials as well as 3 isometric contractions, which were used to normalize data from the hand gripping trials. There was a significant decrease in mean EMG as the duration of the work-rest cycle time increased. At each force level, EMG increased as the percentage of work time within the work-rest cycle increased, but to a greater extent at the highest force level. The results of this study suggest that overall muscle effort, and perhaps muscle fatigue, can be reduced most effectively by modifying the force requirements of the repetitive task. Other variables, such as the percentage of work time within a cycle and overall work cycle time have less effect on the EMG activity level. The results of this study have implications for developing strategies to reduce muscle fatigue during repetitive hand gripping tasks in an effort to reduce the effects of cumulative trauma disorders.

Electromyographic effects of ergonomic modifications in selected meatpacking tasks

This project evaluated the feasibility of a new method of collection of electromyographic (EMG) data during working conditions in industry, and quantified the effects of specific job modifications on the EMG activity of selected upper extremity muscle groups. Average root mean square (RMS) surface EMG activity, calibrated to force equivalent units, was collected on 20 workers from three pork processing tasks before and after ergonomic modifications to their tasks. Significant reductions in muscle effort were detected in the biceps and/or wrist and finger flexors after modification for two of the three tasks. This EMG measurement technique can be used to objectively validate reduced muscle effort with ergonomic modifications.

Work-Related Musculoskeletal Disorders in Bricklaying: A Symptom and Job Factors Survey and Guidelines for Improvements

Abstract Workers in the construction trades experience high rates of injury and illness, including work-related musculoskeletal disorders. As the basis for formulating and implementing ergonomics changes to reduce musculoskeletal disorders among bricklayers, a questionnaire survey was conducted regarding work-related musculoskeletal disorders and the troublesome job factors which bricklayers perceived as contributing to those disorders. A two-page questionnaire was mailed out to all members of a Midwestern bricklayers union local. The responses of 39 nonretired bricklayers, having an average age of 45 and an average of 21.8 years of work experience, were analyzed. Results indicated that work-related symptomatic areas, and those accounting for the most reported lost work time and physician visits, were primarily back, neck, and shoulder, and secondarily, elbow and wrist/hand. The survey respondents consistently identified job factors describing awkward postures of the back and shoulder, and handling bricks...

Work-Related Musculoskeletal Symptoms and Injuries among Operating Engineers: A Review and Guidelines for Improvement

Abstract Among construction workers, operating engineers encounter job factors considerably different from those of their counterparts in other construction trades. While many professionals in the construction trades are faced with risk factors for work-related musculoskeletal disorders (WMD) such as heavy lifting, carrying, power tool use, and forceful repeated motions, operating engineers are confronted with more subtle stressors. The sustained and awkward postures they are required to maintain, the controls they are required to operate, and the vibrating environments in which they work are major risk factors for WMDs among operating engineers. This article reviews the current literature and recommendations for improvement. Considering symptom and disability prevalence rates along with biomechanical and physiological considerations, four primary recommendations to reduce WMDs are indicated. Equipment designs should minimize the magnitude and frequency of vibration reaching the operator. Placement of equ...