Rolf Helbig

Effects of vibration on arm and shoulder muscles in three body postures

SummaryThe electromyographic responses of arm and shoulder muscles to vibrations were studied in three postures similar to the postures of drilling in a ceiling, drilling in a wall and drilling in a floor. This experiment was performed within the defined parameters of: vibrational frequency at 30 Hz, acceleration level 40 m·s−2 (rms), pushing force expressed as percentage maximal voluntary contraction, and gripping force which was set at 100 N. The exposure time for each test was 5 min. The general findings from these three body postures show that all the examined muscles were affected by exposure to vibration. The EMG index increased as follows: trapezius muscle 39% (p<0.05), lower-arm flexor muscles 23% (p<0.05), infraspinatus muscle 14% (p<0.05), lower-arm extensor muscles 14% (p<0.1) and biceps muscle 6% (p<0.1). The muscle most affected by vibration was found to be the trapezius muscle. It should be taken into consideration that vibration can be a contributing factor in neck/shoulder disorders among power handtool operators. The general conclusion from this study is that changes in working posture give different transmissions of vibration in the upper extremities. It seems as if the prime movers and muscles with an increased muscle length or increased degree of contraction are most affected by vibration.

Body Posture as an Indicator of Workload in Mental Work

Objective: For this article, the relationships between body posture and workload for four mental tasks simulated on a computer were studied. Background: Human behaviors are observable during work and are related to human mental activities. A novel supplementary method, based on human behavior but not directly related to task execution, is proposed to assess the workload in mental work situations. Method: Body posture was quantitatively analyzed with the use of a video-based analysis system. The distance between a participant’s head and the display, the distance between the shoulder and the hip, and the trunk angle of the shoulder and the hip with respect to the gravitational field were calculated. Results: The various tasks affected the distance between the head and the display (p < .001) and the trunk angle (p < .001). The distance between the head and the display decreased with increasing workload (p = .007). Conclusion: These results indicate that body posture can be used as an indicator for overall workload assessment. Application: The proposed method of workload may be useful for real-time observations or the monitoring of mental states in mental work environments (e.g., rail traffic dispatching, air traffic control).