The concept only took about 15 minutes to come up with.

I realized if you pay them, they will come.

As humans walk, they vault over their extended leg, causing the hip to rise 5-7 centimeters on each step. Since the backpack is connected to the hip, it to must be lifted 5-7 centimeters. It is this vertical movement of the backpack that ultimately powers electricity generation.

Metabolically speaking, we've found this to be much cheaper than we anticipated. The energy you exert could be offset by carrying an extra snack, which is nothing compared to weight of extra batteries. Pound for pound, food contains about 100-fold more energy than batteries.