An implantable device that can automatically monitor and record patient activity as sensed by an activity monitor. In certain variations, the activity monitor can include an accelerometer providing three-axis acceleration signals and in other variations the activity sensor can include a position sensor, such as a GPS receiver. The implantable device automatically determines if patient activity exceeds a determined threshold and monitors and records a total equivalent distance traveled for a determined period, which may be set equal to a standard measure such as a six minute period. The device can monitor and record multiple periods of activity and the periods may be consecutive, overlapping, and/or separate in time. The device may store all activity records or selected records which may correspond to daily, weekly, or other periodic maxima.