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 years as either both hands moving in a parallel manner, simultaneously in and simultaneously out, or both hands moving in an alternating pattern, one hand goes in while the other goes out. This principle was reexamined with 109 subjects performing the Both Hands task 16 times for each approach on a Purdue Pegboard. A learning curve was fit to each set of 16 trials, and then, various parameters of the curve tested for significance. Females were significantly faster (4%) than males, but the difference diminishes with more trials because of a faster rate of learning for males. Although, parallel motion was roughly 1% faster than alternating motion, 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.