In the past two decades, the miniaturization of highly functional electronic devices has yielded the present condition where such devices are light enough, have a long enough battery life, are robust enough, and even stylish enough to be utilized for extended periods of time. Such devices can monitor activity and various bodily vital signs, and/or provide assistive actions. Due to the interrelationship between persons and assistive electronic devices, it is examined whether the actions (human motion) themselves can be used to power the electronic devices assisting those very actions. Such functionality results in a synergistic win-win interaction, rare in energy systems where trade-offs are pervasive. These interactions are studied in the context of the three types of solution spaces in implantable (inside the body), wearable (on the body), and peripheral (outside the body) devices. Specifically, it is studied whether heartbeats can power the pacemakers regulating the heartbeat; whether walking can power the portable communication equipment guiding the path; and whether movement within a smart building can power the occupancy measurement in automatic occupancy-drive lighting and climate control systems making the building habitable yet energy efficient. Novel energy harvesting solutions are developed for each category, with the impetus of harvesting sufficient energy to perform the desired function without encumbering the body.