The Human-Powered Home describes the heel-strike generator, which was developed with funding from the U.S. Department of Defense as a way of harvesting energy from walking. Since the book was published, examples of collecting power from walking or running have multiplied. Most recently, Kenyan entrepreneur Anthony Mutua, unveiled an ultrathin chip that can be inserted into any shoe and used to charge a cell phone, either on the go or after a run or walk.
Meanwhile, the military continues to pursue ways for soldiers to charge small electronics on the go. A recent example is SPaRK (Soldier Power Regeneration Kit) from SpringActive, Inc., which the manufacture claims can generate 3-6 watts of (continuous) power per leg while walking at 3 mph.