Clarification of the 'symmetrical use of both hands' principle of motion economy

Gilbreths' 'symmetrical use of both hands' principle of motion economy has been interpreted over the yeats as either both hands moving in a parallel m anner, simultaneously in and simultaneously out, or both hands moving in an alternating pattern, one hand goes in while the other goes out. This princ iple was reexamined with 109 subjects pet-forming the Both Hands task 16 ti mes for each approach on a Purdue Pegboard. A learning curve was fit to eac h see of 16 trials, and then, various parameters of the curve tested for si gnificance. Females were significantly faster (4%) than males, but the diff erence diminishes with more trials because of a faster rate of learning for males. Although, parallel motion was roughly 1% faster than alternating mo tion, the difference was not significant and was also diminishing with more trials. The result are supported by motor control studies for oscillating motions and lead to the conclusion that either motion is equally economical . Significance: The principles of motion economy are key to successful job re design as part of Methods engineering. Unfortunately, many of the principle s have not been clarified or empirically tested since Gilbreths' time. This study re-examines one such principle, the symmetrical use of both hands, w hich has been frequently misinterpreted over the years.