"And now it’s a Dodge Challenger. "

"I understand your logic, less acceleration on the backpack= less energy exerted fighting gravity since it remains at a static height. The problem is that in order to maintain the static height, the suspension mechanism must disperse the energy that would otherwise be spent creating a shock impulse in the shoulders of the wearer. That shock impulse does not go away, it just slows down and is distributed through the bungees in the suspension system over a longer timeframe. Think of lifting an apple tied to an elastic band vs lifting an apple tied to a string- do you expend less energy moving your hand vertically in the air because the elastic band is between your hand and the load? Now think about moving your hand up and down at the natural frequency of the sprung mass system, such that the apple does not move. Does your hand require any less energy to move? "

"Better idea- why not just remove the teeth? That would completely obviate the need for toothbrushes, and then we could all drink soylent instead of eating solid foods, further reducing our ecological footprint."

"The first law of thermodynamics applies to all forms of energy, not just heat. This mechanism actually incurs a net loss over a conventional pack due to losses in tensioning the bungee cords. If we use your definition of work, a force exerted over a short distance requires less work than the same force exerted over a longer distance.Ignoring your misunderstanding of physics, you’re on the right track with the idea that the suspension system increases the time over which the force must be exerted, however, you’ve come to the wrong conclusion as the net “metabolic energy” expenditure will be identical  or greater. The manufacturer’s claims of saved watts are bullshit."

"The total dynamic load remains the same. The impact load is just being converted from a instantaneous shock to tensioning of a spring over a time interval. The total energy requirements for hauling this backpack, even if we assume that the mechanism has zero weight, are identical."

"Pretty sure the first law of thermodynamics is being violated if this backpack is somehow able to remove “40-80 Watts” from the act of carrying a backpack."