Differences in mouth occlusion pressure and breathing pattern between arm and leg incremental exercise.

The aim of the study was to compare breathing pattern, mouth occlusion pressure, mean inspiratory flow and the ratio of mouth occlusion pressure to mean inspiratory flow at the same power output and carbon dioxide output during arm and leg incremental exercise. Mouth occlusion pressure was used as an index of inspiratory neuromuscular activity and its ratio to mean inspiratory flow as an index of the 'effective' impedance of the respiratory system. Eight normal subjects performed two incremental exercise tests, one with arms, the other with legs, on different weeks and in randomized order, and on two identical cycle ergometers. The power output was increased by steps of 25 W for arms and 50 W for legs every 4 min until exhaustion. At the same power output, oxygen consumption, carbon dioxide output, ventilation, mean inspiratory flow, mouth occlusion pressure, 'effective' impedance (P < 0.001) and respiratory frequency (P < 0.01) were higher during arm exercise than during leg exercise, whereas inspiratory time (P < 0.05) and expiratory time (P < 0.01) were lower. At the same carbon dioxide output, mouth occlusion pressure, ventilation, 'effective' impedance (P < 0.001) and respiratory frequency (P < 0.01) were higher and expiratory time (P < 0.05) was lower during arm exercise. In conclusion, the higher inspiratory neuromuscular activity and impedance of the respiratory system during arm exercise and the differences observed in ventilation and breathing pattern at equal carbon dioxide output seem related to the differences in exercising muscle afferents and the presence of an increased load due to contraction of rib cage muscles to stabilize posture.