The effect of respiratory muscle fatigue on respiratory sensations.

1. Eight subjects maintained maximal inspiratory pressure as long as possible. The subjects accurately judged the pressure developed, but considered that the sense of effort or motor command increased progressively during the contraction as fatigue developed. 2. A reference inspiratory load was overestimated after maximal inspiratory contractions. 3. These findings are consistent with the hypothesis that awareness of the motor command or effort contributes to the estimation of respiratory loads.