Complex sentence: According to Opsvik the feet are the ignored extremities in ergonomics and as our feet and legs have prime responsibility for moving us in all situations it seemed natural for him to make sure that the chair respond to and is controlled by the feet.
Split into simpler sentences: According to Opsvik the feet are the ignored extremities in ergonomics. As our feet and legs have prime responsibility for moving us in all situations it seemed natural for him to make sure that the chair respond to and is controlled by the feet.