Figure 2From: Loading and unloading breathing during exercise: respiratory responses and compensatory mechanisms Breath-by-breath responses of mouth pressure (P Im ) to abrupt substitution of the gas mixtures for room air (and vice versa ) during steady-state exercise. Values represent means ± SD, 1/2 open + 1/2 solid circles - Room air; open circles - He-O2; open circles with solid triangles - Ar-O2; solid circles - SF6-O2.Back to article page