Human posture is the co-operation of parts of the body to perform a task. This organization is self optimised by the operator to minimize strain and pain and maximize efficiency. This problem is formulated as a problem of inverse kinematic of a redundant robot. Constraints are imposed by the visual and manual task, and criteria may be modified in relation to operator motivation and tiredness. An interactive graphical software is designed to teach the postural problem and as an ergonomic aid.