A final potential method of generating power is to harness air
drag while the user is walking. At a 6 mph run, only 3% of the
expended energy (
) is performed against air resistance [Morton, 1952].
While 30 W of power is a significant amount, little of this energy
could be harnessed without severely encumbering the user. At more
reasonable walking speeds, the available power declines sharply.
Thus, it seems pointless to pursue a hard-to-recover energy source
which can only yield 3% of the user's total energy when leg motion
may consume over 50% of the total energy during the same activity.