Electromyographic evaluation of muscular work pattern as a predictor of trapezius myalgia.

Abstract

VEIERSTED KB, WESTGAARDRH, ANDERSEN P. Electromyographic evaluation of muscular work pattern as a predictor of trapezius myalgia. Scand J Work En viron Health 1993;19:284-90. Electromyographic (EMG) measurements and interviews concerning muscular pain and disability were performed prospectively every 10th week on 30 healthy new female employees of a chocolate manufacturing plant. The static muscle activity and rate of short unconscious interruptions in EMG activity (EMG gaps) of the trapezius muscle during repetitive work tasks were evaluated as possible risk factors for patient status with trapezius myalgia. At the start of employment, the static and median contraction levels were significantly higher in future patients than in the rest of the subjects (nonpatients). In subsequent recordings these values were reduced to the level of the nonpatients. Throughout the study, the future patients had a lower frequency of EMG gaps than the nonpatients. A regression analysis showed a significant value for a low rate of EMG gaps to predict future patient status.Key terms: muscle activity pauses, neck and shoulder disorder, prospective design, repetitive work load, static work load.Occupations with maintained po stures and repetiti ve work tasks are commonly coupled to a high pre valence of neck and shoulder di so rders ( I , 2). Crosssectional studies have shown that pat ients with trapezius myalgia use their muscles at a higher static level than healthy subj ec ts do (3-5). Subjects who ha ve suffered mu scle pain on a previou s occasion, but not during a recording sess ion, have also shown a higher static electromyographic (EMG) level than subj ec ts without sy mptoms (6) . Subjects who hav e experienced muscular pa in ha ve dem onstrated fewer short, uncon sc iou s interruptions in EMG activ ity (EM G "gaps," with a duration of 0.2-2 s) during repetitive work task s than healthy subjects (6). A previous prospective study of the relation bet ween muscular effort during work and subs eque nt pain used video recordings as indirect measurements of mu scle lo ad (7). It found th at relative time with elevated shoulders and a flexed neck was a risk fa ctor.Th e present report is the fir st pr ospecti ve study wi th direct measurements of oc cupati onal mu scular activi ty and an asse ssment of mu scular pain. The development of mu scular pain and subjectively assessed risk factors for trapezius myalgia among workers with rep etitive light manu al wor k in the sa me manufacturing plant ha ve been described elsewhere (2, 8). 284Th e main purpose of thi s paper was to analyze the ass ocia tion between the le vel and pattern of mu scl e usage du ring the performance of a stereotyped job and the development of trapezius myalgia. Subjects and methods Subje ctsFifty-five fem ale workers hired consec utively by a chocolate manufacturing company were included in the study as the y started their employ me nt. Except for three subjects who declined to participate , all of the subjects signed an in formed consent form. The study was ...

Trapezius muscle rest time during standardised computer work – A comparison of female computer users with and without self-reported neck/shoulder complaints

“…As previously presented by Veiersted et al (1993), lack of muscle rest periods is a plausible risk factor for development of WMSDs. Due to the cross-sectional design of the present study, it cannot be stated whether the cases showed less muscle rest than controls also before the complaints developed.…”

“…Due to the cross-sectional design of the present study, it cannot be stated whether the cases showed less muscle rest than controls also before the complaints developed. Veiersted et al (1993) showed that the number of short muscle rest periods were significantly lower for the patients, also before patient status. Moreover, a prospective study of light manual workers in the poultry and fish industries showed higher mean shoulder muscle EMG activity both prior to and after the start of complaints among workers who later developed neck/shoulder complaints presented, compared with workers who stayed healthy (Madeleine et al, 2003).…”

“…Based on this theory, it has been hypothesised that a low degree of muscle rest is a risk factor for development of WMSDs. This hypothesis is supported by a one-year prospective study of light manual work (Veiersted et al, 1993), where surface electromyography (EMG) was recorded and a regression analysis showed that a low amount of short muscle rest periods (gaps) predicted future development of WMSDs. More-over, an extensive prospective study of computer users showed a significant association between perceived muscular tension and an increased risk for developing neck pain (Wahlström et al, 2004).…”

Effect of mental and physical demands on muscular activity during the use of a computer mouse and a keyboard

“…A muscular activity pattern with almost no EMG gaps may be crucial, as it has been shown that few EMG gaps may be related to the development of work-related musculoskeletal symptoms (23). One of the mechanisms behind this relationship may be an association between EMG gaps and the rotation of motor unit recruitment (24), which thus possibly prevents the overload of muscle fibers.…”

Interindividual variation of physical load in a work task

“…In a prospective field study of repetitive industrial work, the muscle activity pattern had predictive value (15). Some studies show no unambiguous associations between EMG data and disorders (16,17).…”