All subjects received a brief physical screening by the principle
investigator to confirm the established inclusion and exclusion
criteria. Height and weight were measured and active range of
motion of the upper extremities was visually screened. Female
subjects wore a sleeveless tank top and male subjects exposed their
upper body. The skin area for EMG was prepared with alcohol, after
shaving when necessary. Isometric lifting capacity at the shoulder
level was tested with fully extended elbow and with both feet
together. Subjects were asked to pull a bar attached to a load cell
with a non-elastic strings for 5 s with keeping the trunk in erect
posture. Maximal muscle contraction levels while testing the
isometric lifting capacity was collected to normalize the EMG data
and to estimate the amount of weight to be used for Light and
Heavy lifting conditions.