The invention relates to a system for detecting respiratory muscle activity of a patient (1) receiving assisted breathing, which is connected to an assistance device (2) by a pneumatic circuit (3). Said system is characterised in that it comprises: a means (4, 5) for acquiring air pressure and flow signals in the pneumatic circuit (3), sent to a means (6) for continuously estimating the theoretical air pressure expected in the pneumatic circuit in absence of respiratory muscle activity from the patient and a means (7) for comparing estimated and actual theoretical pressures in order to continuously detect a pressure differential showing respiratory muscle activity in the patient.
