I'm poor at mechanics but afaik in racing it's considered that extra suspension absorbs energy, making the car slower. So my intuition is that the bungee cord w

I'm poor at mechanics but afaik in racing it's considered that extra suspension absorbs energy, making the car slower. So my intuition is that the bungee cord would heat up from expanding/contracting, while taking energy for that from the person. Not sure, though, how that compares to lifting the entire weight. But then again, what happens when the person is already on a downswing and the cord belatedly jerks the backpack up?