Figure:
Empirical data taken for a 58.7 kg man of
effective force perpendicular to the ground on the foot while walking
(from [Braune and Fischer, 1987]). This data curve should scale roughly based on weight.
Using the legs is one of the most energy consuming activities the human body performs. In fact, a 68 kg man walking at 3.5 mph, or 2 steps per second, uses 280 kcal/hr or 324 W of power [Morton, 1952]. Comparing this to standing or a strolling rate implies that up to half this power is being used for moving the legs. While walking, the traveller puts up to 30% more force on the balls of his feet than that provided by his body weight (Figure 1). However, calculating the power that can be generated by simply using the fall of the heel through 5 cm (the approximate vertical distance that a heel travels in the human gait [Braune and Fischer, 1987]) reveals that
of power is available. This result is promising given the relatively large amount of available power compared to the previous analyses. Even though walking is not continuous like breathing, some of the power could be stored, providing a constant power supply even when the user is not walking. The following sections outline the feasibility of harnessing this power via piezoelectric and rotary generators and present calculations on harnessing wind resistance.