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.

Effects of vibration frequency and postural changes on human responses to seated whole-body vibration exposure.

The present investigation evaluated the effects of changes in pelvic orientation and vibration frequency on the seated human's response to wholebody vibration (WBV). Seat-to-trunk and seat-to-head acceleration transmissibility, peak-to-peak pelvic motion and erector spinae EMG and mean erector spinae EMG was collected across three pelvic orientations (9 degrees anterior pelvic tilt, neutral pelvis, and 9 degrees posterior pelvic tilt) and frequencies ranging from 4.5 to 16 Hz. Subjects included 30 healthy males between the ages of 18 and 35. Ensemble averages, two vibration cycles in length, were produced for each subject within each frequency-pelvic orientation combination. Group ensemble averages within each frequency-pelvic orientation combination were then compared using ANOVA. Changes in pelvic orientation produced significant differences in acceleration transmissibility, pelvic motion, and erector spinae EMG. At frequencies below 6 Hz, acceleration transmissibility at the head and pelvic motion were significantly greater in the posterior pelvic orientation than in the other two. At frequencies above 6 Hz, acceleration transmissibility at the head and trunk were significantly greater in the anterior pelvic orientation than in the other two. Peak-to-peak EMG responses were similar across all pelvic orientations at frequencies below 6 Hz. However, above 6 Hz, the response was significantly greater in the anterior pelvic orientation than in the other two. Thus, vibration frequency and pelvic orientation were shown to have significant interactive effects on the seated human's response to WBV. These interactive effects need to be considered when determining appropriate vibration exposure guidelines.

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.

Active surveillance for the control of cumulative trauma disorders: a working model in the newspaper industry.

Health and risk factor surveillance is a critical aspect of an effective ergonomics process. Physical therapists are becoming increasingly involved in many components of the ergonomics process, including health and risk factor surveillance. The purpose of this study was to develop and implement a multistaged active surveillance program for the management and control of cumulative trauma disorders. The surveillance program was established at three newspaper companies consisting of 1,150 employees. This study focused on the first three stages of the multistage surveillance model, which incorporates the use of symptom and job factor questionnaires, specific anatomical surveys, and clinical detection tests. The results of the study indicated that 1) musculoskeletal symptoms in the back, neck, and hands accounted for the majority of reported missed work among the newspaper workers; 2) production workers had a higher prevalence of musculoskeletal symptoms than office workers; and 3) the prevalence of probable carpal tunnel syndrome among the newspaper workers was 1.5%.

Effects of stair-stepping exercise direction and cadence on EMG activity of selected lower extremity muscle groups.

Step ergometry has become a popular treatment mode in cardiovascular fitness and knee rehabilitation programs. The following study describes the effects of forward stair stepping at 35 and 95 steps/minute and forward and retrograde stair stepping at 60 steps/minute on the mean electromyographic (EMG) activity of the gluteus maximus, rectus femoris, vastus medialis, semimembranosus/semitendinosus, and gastrocnemius muscles. Thirty-three subjects without prior lower extremity pathology participated in the study. Analysis of variance was used to compare mean EMG activity during the knee extension phase of the different stepping conditions. Significant differences (p < 0.05) in mean EMGs of gluteus maximus, rectus femoris, vastus medialis, and gastrocnemius were noted across all cadences. The semimembranosus/semitendinosus EMG activity displayed a single significant difference between the cadences of 35 and 95. The comparison between forward and retrograde stepping identified only one significant difference in mean EMG (semimembranosus/semitendinosus). The effects of cadence on EMG activity should be considered when developing conditioning or rehabilitation programs for the lower extremity. Faster cadences result in increased peak activity of shorter duration for the gluteus maximus, quadriceps, and gastrocnemius. There is no apparent difference in EMG activity of the hamstrings due to cadence. Also, noting the minimal activation that occurs, stair-stepping exercise would not be recommended for strengthening of the hamstrings musculature.

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.

EMG Comparison of Lateral Step-up and Stepping Machine Exercise.

The availability and use of stairstepping machines in both the rehabilitation and fitness industries have seen a significant increase in the last several years. The primary purpose of this study was to evaluate the electromyographic (EMG) activity levels of the rectus femoris (R), vastus medialis (V), biceps femoris (B), gastrocnemius (G), and semimembranosus/semitendonosus (S) muscles during exercise on a stepping machine and during performance of an 8-in lateral step-up. Eighteen subjects, without prior knee pathology, participated in the study. The root mean square EMG activity was obtained using surface electromyography and normalized to percent of maximum voluntary isometric contraction. Each exercise was broken down into knee flexion and knee extension phases for descriptive purposes. Analysis of variance (p < .05) was used for between exercise comparisons. Mean R and V activity were significantly greater during the lateral step-up exercise. Mean G activity was significantly greater for stepping machine exercise. Both B and S showed no significant mean differences between exercises. The stepping machine, in general, showed decreased activity during the knee extension phase and very little activity during the knee flexion phase when compared to the lateral step-up. The results indicate that exercise on the stepping machine would result in a more conservative rehabilitation approach for strengthening the quadriceps and hamstrings. J Orthop Sports Phys Ther 1992;16(3):108-113.

Relationship of extremity muscle torque and bone mineral density in postmenopausal women.

The purpose of this study was to examine the correlations between the torque of four extremity muscle groups and the bone mineral density (BMD) of the lumbar spine and hip in postmenopausal women. Fifty-six postmenopausal women (means age = 55.4 years, s = 7.1; means height = 162.6 cm, s = 6.4; means weight = 65.9 kg, s = 9.3) served as subjects. Bone mineral density was measured from the L2-L4 vertebral bodies, greater trochanter, femoral neck, and Ward's triangle using dual-photon absorptiometry. Hip abduction, knee extension, hip flexion, and grip force were assessed using the Spark Muscle Examination and Exercise Dosimeter (MEED) 3000 system. The Pearson product-moment correlations between muscle torque and BMD ranged from .07 to .42. The significant (p less than .05) correlations between torque and BMD (r = .27-.42) occurred in functionally and anatomically related areas. Results of this study demonstrate a statistically significant relationship between torque and BMD in anatomically related areas in postmenopausal women. This relationship, however, is not sufficiently strong to allow for prediction of BMD from the four muscle groups tested in this study. The relationship does suggest that strength may be a factor in the determination of BMD. Maintenance of strength in those muscle groups with anatomical or functional relationships to the hip and lumbar spine may play a role in the prevention and cessation of the osteoporotic changes that occur.