therbligs

Therbligs are a set of elemental motions used in time-and-motion study to analyze manual work. The term was introduced by Frank B. Gilbreth and Lillian M. Gilbreth in the early 20th century. The word therblig is “Gilbreth” spelled backward with a rearrangement, chosen to name these primitive motions. The original system defined 18 basic motions that together comprise most manual tasks, covering actions such as reaching for an object, transporting or moving it, grasping, using a tool, positioning, releasing, and inspecting; other motions include seeking, planning, waiting, and resting. Each therblig is associated with a symbol and a standard duration, used to study and optimize work.

In practice, analysts break tasks into therbligs by observing work, or filming it and labeling the motions, in order to identify unnecessary or inefficient motions. This information can guide redesign of tools, workplaces, and tasks to reduce fatigue and increase productivity. The therblig concept played a central role in early industrial engineering and educational programs, influencing time studies, motion studies, and ergonomic design. While influential, the approach has limitations: it often oversimplifies cognitive aspects of work, and critics note that it may not capture modern tasks that involve complex decision-making or digital tools. Consequently, therbligs are now primarily of historical interest, studied as part of the development of human factors and methods-time measurement (MTM) used for task analysis.