This paper presents a battery-less wireless sensor network (WSN) equipped with electromagnetic (EM) energy harvesters and sensor nodes with adjustable time-interval based on stored the energy. A wearable EM energy harvesting system is developed and optimized to power-up a typical wireless sensor mote from body motion. This is realized through characterization of the body motion and design of a compact EM energy harvester according to vibration frequencies generated during human running and walking. The harvesting system provides self-initiating and regulated supply voltage through rectifying, charging buffer capacitance, and buck DC-DC converter. The proposed system provides maintenance-free operation and adjustment of the sensing-rate according to jogger activity. It is shown that energy-level-based adjustment of the sensing and transmitting time-interval can prolong the lifetime of the battery-less sensor node. It is experimentally demonstrated that the presented WSN measurement nodes provide reliable and long-term operation as attached to human body, proving the feasibility of the system as a wearable battery-less sensor network. (C) 2016 Elsevier B.V. All rights reserved.