Assuming that employees have adjustable chairs of the right size, they then must be able to make effortless changes in posture during cross performance. They should not have to stop what they're doing and adjust their chairs every time they change to another task. For reasons of efficiency and practicality, the chair should be designed to allow spontaneous postural movements that support the flow of performance. Ergonomists are still debating the Mandal and Grandjean theories of optimal posture at work. Mandal advocates a forward-sloping seat that keeps the back upright and tilts the thighs forward.
Grandjean proponents say the position puts too much pressure on the legs.
They favor a neutral to backward tilt, citing studies which show that VDT workers in particular spend a large part of the day reclining to do their work. Rather than continue such polarization, it would seem more helpful to recall what Charles Eames said about designing chairs for how people sit rather than how they should sit. Time-lapse photography of employees working on computers shows them going through a continuum of postural changes from Mandal to Grandjean. Based on how people sit, there is no one right posture for productive cross performance. Instead of prescribing posture, a cross performance chair supports many work styles.