Respiratory motor output during an inspiratory capacity maneuver is preserved despite submaximal exercise

- Diaphragm EMG reached a plateau during either 80% or 60% constant work rate exercise tests.
- Plateau of the diaphragm EMG during exercise does not mean that there is neural inhibition.
- Inspiratory capacity maneuver seldom entails a maximal effort even in well trained normal subjects.

It is unknown whether respiratory motor output is constrained during exhaustive exercise in healthy adults. We hypothesised that neural inhibition did occur; to test this hypothesis we measured diaphragm EMG from a maximal inspiratory capacity maneuver (EMGdi-IC) at rest and during exercise. EMGdi-IC was measured before and after the amplitude of the diaphragm EMG entered a plateau phase in eleven healthy adults undertaking exercise at 60% and 80% of maximal workload achieved from incremental exercise. The mean EMGdi-IC at rest was 65 ± 16% of the maximum that could be obtained from a battery of inspiratory tasks. Before and after the plateau phase of diaphragm EMG, EMGdi-IC was 68 ± 13% and 72 ± 12% (p > 0.05) during 60% of the maximum workload, and was 70 ± 13% and 78 ± 13% (p > 0.05) during 80% of the maximum workload achieved on an incremental test. A further sub-study in which 5 participants exercised at 90% of the maximum workload also showed that EMGdi-IC was not diminished during exercise. Our data show that exercise condition does not reduce the magnitude of EMGdi-IC. This argues against neural inhibition as feature of submaximal exercise in healthy adults.