Effect of hand loads on upper extremity muscle activity during pushing and pulling motions.

Manual pushing or pulling with a hand tool is a coordinated action by various upper extremity muscles. The objective of this experimental study was to examine the effects of horizontal and vertical hand loads on upper extremity muscle activity during concentric pushing and pulling exertions. Twenty young female participants conducted repetitive pushing and pulling trials with three horizontal loads (1 kg, 2 kg, 3 kg) and two vertical loads (0.6 kg, 1.3 kg) in a seated posture, while the myoelectric activity of seven upper extremity and shoulder muscles were quantified. Study results indicate that the shoulder flexor and extensor muscles were more strongly associated with horizontal load, and elbow flexors were more sensitive to vertical load. The empirical data from this systematic evaluation can offer initial insights for ergonomic design and evaluation of hand tools or occupational tasks that involve repetitive pushing or pulling.