Figure 1.

A, level treadmill at a slow speed requiring a = 1 l min⁻¹. B, level treadmill at a faster speed requiring a = 2 l min⁻¹. C, inclined treadmill at the same speed as in A requiring a of 2 l min⁻¹. A–C are excerpts from Casey et al. (1977). D, the tandem chair couples the legs of the experimenter and subject (yellow highlight) and allows the experimenter seated behind the subject to move the subject's legs passively. E, 10 s binned mean (SEM) results from 10 subjects showing the transitions: ventilation (top), breathing frequency (middle) and tidal volume (bottom). At both transitions (red arrows) first from rest to passive movement and then from passive movement to active exercise, ventilation increases quickly. F, the 10-subject mean (SEM) changes in breathing at the exercise transitions shows that rest to passive movement (R-P), and passive to active movement (P-A) sum (R-P + P-A) to equal the rest to active exercise transition (R-A). E and F are excerpts from Bell & Duffin (2006).