A method for automatically determining the ventilatory (or “anaerobic”) threshold breakpoint for adaptive rate pacing without the need for directly measuring anaerobic threshold or ventilatory threshold comprises: (a) positioning a first sensing electrode in the heart or superior vena cava of a patient carrying an implanted pacemaker, the first sensing electrode connected to the implanted pacemaker; (b) positioning a second sensing electrode in the thoracic region of the patient and spaced apart from the first sensing electrode; (c) determining the chest wall impedance of the patient between the first sensing electrode and the second sensing electrode; (d) measuring the ventilation (e.g., the minute ventilation) of the subject from the chest wall impedance during submaximal exercise by the patient; and then (e) determining the ventilatory threshold breakpoint of the patient from the measured ventilation. In the pacemaker, the adaptive rate pacing is preferably based on measured chest wall impedance, with pacing rate increasing as exercise or metabolic activity sensed thereby increases. The implanted pacemaker is then preferably programmed, preferably automatically, so that the rate of increase in pacing rate in response to increasing ventilation by the pacemaker is attenuated after the breakpoint is reached. Peak ventilation is preferably also determined so that the maximum pacing rate of the pacemaker output is matched to the peak ventilation during adaptive rate pacing from the pacemaker. Apparatus implementing the method is also disclosed.