This paper proposed a hybrid energy harvesting interface for wearable electronic devices, which achieves the simultaneous harvesting of piezoelectric and thermoelectric energy from the human body. The interface employs an inductor-shared converter with maximum power point tracking (MPPT) assistance to convert the piezoelectric energy rectified by a parallel synchronized switch harvesting on capacitor (P-SSHC) rectifier and the thermoelectric energy into a regulated output. The harvester employs an adaptive switching cycle (ASC) scheme to reduce the ripple of the tracking to improve the MPPT accuracy and end-to-end efficiency. In parallel, for efficient harvesting of both sources simultaneously, a multiplexed MPPT technique is incorporated into the harvester to reduce the chip area. In addition, to reduce the power loss resulting from the sampling phase of the FOCV method, a single-cycle fast-sampling technique is employed to assist the piezoelectric energy harvesting. The proposed hybrid energy harvester is fabricated by a $0.18 \mu \text{m}$ CMOS process with a core area of $1.2 \times 0.7$ mm². The measured results show that the peak tracking efficiency of the PZT and TEG is 99.58% and 99.37%, respectively. The peak of end-to-end efficiency of the interface reaches 86.67%.