Go on give your patients some privacy. Here the walkway is 39m long 2.8m wide and 2,82m high. The full distance is used for EMG gait analysis. Usualy the subject walks 4.7m before and 3.7m after the field of view of the cameras. No force plate used for gait analysis but 2 Kistler force plate for posture and balance analysis.
Most labs are small because they tend to be retrofits in to an older building.
There are 2 factors to consider when answering the question. The 2nd is equipment requirements and field of view size. With our CODA mpx30 we can create a slightly larger than 2 x 2 x 2 m field of view by having the sensors 6 m apart. With our Selspot II the field of view tended to be 2 x2 x 1.5 m because of the limited focal distance. In my view for all types of walking this is a good size.