The effects of armrests and high seat heights on lower-limb joint load and muscular activity during sitting and rising

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Abstract
The loading moment of force on the hip, knee, and ankle joints of nine healthy men rising from four different types of stools were compared, together with the levels of myoelectrical activity (EMG) in four leg muscles. Two types of stool (stand stools) had higher seats than a normal chair. The other two were of ordinary seat height, but one also had armrests. The bodyweight carried by the different stools when sitting was also measured, and the subjects estimated the effort required for each trial. The mean maximum knee moment was over 60% lower when rising from the high stool than from ‘ordinary’ seat height. The difference between the high and low stand stool was also significant (pp<0·00l). The rectus femoris muscle was little activated and the semitendinosus muscle was activated earlier when rising from higher seat heights. All subjects estimated the effort of rising from the higher stand stool to be lower than from the lower stand stool or from ‘ordinary’ height without arm rests. It was concluded that stand stools are good alternatives for workers who change frequently between sitting and standing work.