Local muscular strain dependent on the direction of horizontal arm movements

Abstract

Manual material handling still plays an important role in assembly work as well as in the service industry. By means of an ergonomic layout of working places, the effects of disadvantageous working conditions, especially static load resulting from unfavourable postures of the body as well as unnecessary physiological cost arising from body movements may be avoided. In this context knowledge about the optimum directions of horizontal arm movements is fundamental. Therefore by means of advanced methods of multi-channel electromyography (EMG) and applying computer assisted evaluation methods, physiological responses to one-handed horizontal material handling in a sitting position were recorded. In order to obtain myoelectric signals from the most important task-relevant muscles out of more than 40 muscle groups of the hand-arm-shoulder-system, preceding research was done also aiming at standardized lead positions for surface EMG. Groups of five young females each participated in a series of successive experiments, in which the direction of movements of the left arm was varied. The subjects worked without and with an external load imposed by weights of 0, 1, 2 and 4 kg. The movements between 20 degrees and 230 degrees--measured from the frontal plane of the subjects--included working from ahead and from behind. The lifting distance was 38 cm starting from different outward points within the reach to a fixed point near the body. Also in one test series the handling frequency was varied between 12, 24 and 48 lifts per minute. Assessment of the physiological cost by electromyographic activities (EA), especially the determination of the most stressful and least expensive directions of repetitive horizontal movements, was more effective when differentiating static and dynamic portions of muscular strain than common means of EA.

Effects of cooling and clothing on vertical trajectories of the upper arm and muscle functions during repetitive light work

“…Literature regarding the eVect of cooling on EMG activity is contradictory, but several authors have found that EMG activity is increased in cold conditions (Petrofsky and Lind 1980;Winkel and Jørgensen 1991;Hammarskjöld et al 1992;Meigal et al 1998;Oksa et al 2002;). It has also been shown that muscular strain depends on the direction of movement (Strasser and Keller 1989), and movement in a 30° direction in the horizontal plane causes less than half of the muscular load compared to directions between 90° and 160° (Strasser and Muller 1999). The results of this study support this Wnding, since the increase of a-EMG was signiWcantly higher particularly at extreme angles of the trajectories (200° and 220°).…”

Musculoskeletal risk factors in cleaning occupation—A literature review

“…Low back disorders have been associated with working in a forward, bent position (Vinga˚rd et al, 2000). In other studies the relationships between poorly designed workplaces resulting in poor posture and disorders of the musculoskeletal system have been described (Kilbom, 1988;Louhevaara et al, 1990;Ohlsson et al, 1989;Strasser et al, 1989).…”

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

“…5,6,28 The APDF model, which was described and illustrated by Jonsson,29 states that the static level of muscle activity is the percentage of MVC that is below the lowest 10% of the cumulative RMS EMG signal, whereas the dynamic level (90th percentile APDF) is the percentage of MVC that is above the greatest 10% of the cumulative EMG signal.…”