Per the disclosure subcutaneously implantable medical devices (IMDs) with rate responsive implantable pulse generator (IPG) capability that also include dual patient activity sensors are adaptively controlled. One of the activity sensors uses multiple electrodes adapted to acquire electrocardiographic signals and signals from non-cardiac muscle tissue (myopotentially-based signals). The signals from the electrode-based activity sensor are used to confirm and/or override the patient-activity sensor signals from the other non-myopotentially-based patient activity sensor. The electrodes are directly mechanically coupled to the housing of the IMD and electrically coupled to circuitry that filters, processes, and interprets both the patient activity sensor signals.