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Comment by hammock | Hacker News Reader

Eight gallons of gasoline

Humans are much more energy efficient than cars, so it was less than 3/4 of a gallon (100 kcal/mile * 200 miles = 20,000 calories = 0.7 gallons of gas or about 6 pounds of body fat). He's probably much more efficient than 100 kcal/mile though.

Energy efficiency per distance of running improves very little with training. According to the book “Burn” by Herman Pontzer we are talking about few percents, not even 10%.

That is presumably talking about differences in metabolic and mechanical efficiency, but assuming those are held equal, energy output still scales linearly with work performed, which is directly proportional to body mass, and energy loss from atmospheric and wind drag is going to operate similarly. Simply being smaller and having a slimmer profile will result in less energy needed per unit of distance compared to an average person.

That said, Aleksandr is smaller than an average 40 year-old man, but actually pretty large for a distance runner, 20 kg heavier than the current world record holder in the marathon.

That book described total energy expenditure for an individual per distance traveled. It does not improves much even after years of training. It is interesting that for running the efficiency does not depend on speed as wind drag does not contribute much below 20 km/h. This is different from walking. Walking at relaxed pace is the most efficient and uses 2 times less energy per distance than running. At about 7 km/h walking becomes less efficient than running.

Just being skinny probably makes him more efficient than average.

When I was cycling I was joking that the bike is not much greener than the car, because it burns 4 ribeyes/100km or 17 miles/ribeye.

I read somewhere that if you’re not at least mostly vegan, e-bikes actually have lower lifecycle carbon emissions than bikes because you end up burning fewer calories and eating less (assuming you don’t substitute in more exercise).

That makes a lot of sense. Intuitively (I haven't tried to run numbers on this), the big efficiency problem with a car – gas or EV – is not that it's using "unnatural" forms of power, it's that you're hauling a 3000 pound vehicle around with your 160 pound human. It's easy to believe that photovoltaic power -> modern battery -> electric motor is far more efficient than photosynthesis -> animal digestion -> human digestion -> human muscle. I wouldn't be shocked if that held up even on a vegan diet, though the difference would be a rounding error compared to the emissions from other aspects of our lives.

It’s plausible especially if you use PVs to charge. But what about the costs in producing and disposing of the batteries?

So. Lithium battery powered humans would emit less carbon than regular humans?

They would since we could charge them using PV instead of wasteful bovines.

Yes, sedentary lifestyles require less overall energy input vs. active ones

If we consider the average diet bikes are still around 1/3 the emissions of cars per mile. Obviously if you eat only meat that gets worse but I doubt it’s possible to exceed car emissions this way.

This has some data: https://keith.seas.harvard.edu/blog/climate-impacts-biking-v...

According to Table 1, a meat eating biker emits more CO2, than a double-occupancy Prius.

I suspect an EV would completely tip the table in favor of driving.

Side note - comments like this are why I come to HN. Thank you.

That's not true, Humans are not more energy efficient than cars. Rather Humans are lighter than cars.

A car as light as a human would get something like 1,000mpg (probably a fuel cell with an electric motor).

https://sites.google.com/view/ebikestudy

That's a bit like saying a Honda Civic aren't more efficient than an Abrams tank because the Civic weighs less. They don't have the same capabilities, but one is gonna win on MPG for sure.

Doesn’t this ignore the energy loss from eating and growing the food?

Yes, it does

It's 8 gallons if he were to drive. Cars weigh more, but the human body doesn't have an internal combustion engine built into it.

This is a frighteningly-cool insight. If I think about a single marathon, that's roughly 1 gallon of gas for my own car. I don't know how to translate that to human fuel, but it is crazy to me to think that that is not an insignificant amount of fuel the human body needs to burn to do the equivalent of a car.

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