Classification of human motions

Stages in the development of the classification for human motions are reviewed from the 17th century up to the present day, with special emphasis on the discrete events approach to the classification of human motions as advocated by the Gilbreths. It is put forward that this approach is inappropriate both from the psychological and the physiological view point; while at the same time it is emphasized that, although the therblig approach contributed significantly to the understanding of human motions and skills, nevertheless it may be more harmful than beneficial in the long run. The additive properties of the discrete events approach to the analysis of human motions are considered. Results of the investigations reported here suggest that, in the performance of repetitive tasks of the nature described here, the therblig times of the task are independent units within a work cycle, when analysed by means of 100 cycles. Thus, the times are additive in the mathematical sense, but when the same task is repeated only once, or a very few times, and analysed by single cycles, the therblig times form an integrated part of the entire work cycle and, therefore, their times are not additive in the mathematical sense.