This paper presents an efficient hybrid energy harvesting interface to synergistically scavenge power from electromagnetic (EM) and piezoelectric (PE) sources, and drive a single load. The EM harvester output is rectified through a self-powered active doubler structure, and stored on a storage capacitor. The stored energy is then transferred to the PE harvester to increase the damping force and charge extraction. The total synergistically extracted power from both harvesters is more than the power obtained from each independently. The hybrid operation is validated through a compact and wearable platform that includes custom designed EM and PE harvesters for scavenging energy from human motion. The system supplies 1-3.4 V output for powering up wireless sensor nodes with a wide range of vibration frequency, and generates between 1-100 mu W at 90% maximum power conversion efficiency. The solution has superior power generation performance compared to previous stand-alone systems in the literature.