A study was conducted to determine the effect of varying magnitude of load
and work rate on muscular strain in seated manual handling tasks performed
with one hand. The study also investigated the effect of direction of movem
ent on muscular strain. Ten subjects (males and females) participated in th
e study who performed the task of moving weights from a conveniently locate
d outwards position to a point closer to the body midline. Subject used the
dominant hand to perform the task and handled weights of magnitude 1 and 2
kg at the work rates of 10 and 20 movements/min. Starting positions were f
ixed at 45 degrees, 90 degrees and 150 degrees with respect to the body mid
line. The distance over which weights were moved was fixed at 38 cm. Using
a metronome precisely controlled the pace of the work. Subjects worked at a
n adjustable work station and adjusted it until their elbow height and tabl
e height were at the same level. Electromyography (EMG) activity was record
ed from 5 muscles of the dominant arm-shoulder region using a computerised
data recording and analysis system. Root-mean-squared (RMS) values of EMG s
ignals were computed to compare the influence of experimental conditions on
muscle strain. Static, dynamic and mean components of EMG activities were
obtained. Total muscle load was also determined. Results of the study show
that muscular strain as measured by EMG activity was in general sensitive t
o Variations in magnitude of load and work rate. Work rate had relatively l
arge influence on muscular strain as compared to magnitude of load. The res
ults of the study indicate that the total muscle load was dependent on the
direction of movement. Individual muscle strain also showed some direction
of movement dependence though the results varied from muscle to muscle. The
results of the present study have been compared with other published studi
es and suggestions for future work have been given.