A novel power optimization technique, called adaptive tracking is proposed in this paper for successive approximation analog-to-digital converters aiming implantable device applications. A SAR-ADC can easily be equipped with the proposed tracking technique by a minor modification in its digital circuitry (SAR). This work relies on the similarity of consecutive sample values in band-limited bio-potentials. The proposed adaptive tracking scheme can reduce power consumption of a wide variety of SAR-ADCs. In particular, we show that the tracking scheme can save 30% of power in a conventional SAR-ADC, 31% of power in those using binary SAR-ADCs using a weighted DAC with split MSB capacitor, and 8% of power in those using charge sharing DAC.