Local muscle and circulatory strain in load lifting, carrying and holding tasks

Abstract In order to quantify local muscle and circulatory strain in manual handling, continuous parcel lifting, carrying and holding tasks were simulated in the laboratory. In the tasks the parcel weighed 4 kg, and the set maximum work time was 30 min. The subjects were six female (age 26–41 years) and six male (age 32–41 years) volunteers. The maximum work time and the local ratings of perceived exertion (RPE) showed that strain on the back became intolerable after holding for 7.6±4.5 min . According to the EMG amplitude distribution probability function (related to muscle force, %MVC) in each task, strain for at least two of the studied muscles (brachioradialis, upper trapezius, erector spinae (L3 level), and semitendinosus) was too high at the static (over 5 %MVC) and/or median (over 14 %MVC) contraction levels. Heart rate, blood pressure and the overall RPE indicated that average circulatory strain in the tasks was low. Strain was significantly higher during lifting than holding, and the difference was accentuated if a subject used the leg lift technique. There were only few differences in local and circulatory strain due to sex. To prevent the development of excessive local muscle strain in these types of tasks the work pattern should be individually adjustable, and include sufficient rest pauses.