I wondered… If we measured the energy efficiency of humans the way we measured it for cars, how efficient would a human be??
The way we casually measure how efficient a car is in miles per gallon of petrol, lets see how many MPG humans get.
So firstly we have to make some assumptions.
Cars eat petrol, it’s their favourite, unless they are ‘vegetarians of the car world’ and eat Diesel or LPG. We don’t have to assume this.
Humans; can’t eat petrol. Lets just assume that petrol is amazing, we can digest it, and Starbucks will sell you a nice ‘gasacino’.
Lets find our average human, the equivalent of the ‘Volkswagen Golf’ of the car world.
After reading a lot of ‘The average UK male is:’ articles from various crappy newspapers, I’m going to assume that the average person is:
Male, 30 years old, weighting 12 Stones, 10 Pounds and is 5 ft 10″ Tall and in a reasonable state of health.
First we need to find out how much energy in Kcal this human uses just by being alive in a day. This is called the BMR (Base Metabolic Rate) and can be worked out using the ‘Harris Benedict Equation’
BMR = 88.362 + (13.397 x weight in KG) + (4.799 x height in cm) – (5.677 x age in years)
In this case the BMR for our human is: 1,852.98 Kcals
At this point I’ve started to realise that being British is a pain in the arse, we have a messed up system where we measure some things in imperial measurements and some in metric.
Now we need to work out how many calories our human will burn whilst running for 1 mile. At this point I want to give our human a name. According the the internet the most popular name for boys in 1985 was ‘Michael’ so that’s how we’ll now refer to our human.
We need to know how long it will take Michael to run his mile. According to running websites the average pace for a normal person is 8 Minutes per mile. This means he’ll be running at a speed of around 7.5MPH
To work out how many calories Michael will use when running his mile, we need to know how much energy Michael will be metabolising whilst running. Apparently the measurement for this is done in METs (Metabolic Equivalent of Task) According to “The Compendium of Physical Activities, 2011” running at 7.5MPH uses 11.8 METs.
According to the good people at Casio we can work out the amount of calories Michael uses during his run with the following equation:
Kcal = BMR x METs/24 x hour
When rounded up to the nearest Calorie, we can say that Michael will burn 121Kcal whilst running 1 mile, and it’ll take about 8 mins.
The internet tells me that petrol has an energy density of 32.4MJ (Megajules, not Michael Jacksons) per litre. Google converter is absolutely sure that 1MJ = 238.85 Kcal.
So 1 Litre of petrol = 238.85 * 32.4 = 7738.74 Kcal
Google converter is also insisting that 1 Imperial gallon = 4.55 Litres, which means in one 1 gallon of petrol there is 35,211. 27 Kcal (but no carbs so it’s ok!)
Now we need to simply work out:
Calories in a gallon of petrol / Calories that Michael burns from running 1 mile in 8 mins (at a rate of 11.8Mets)
Which is… 291
If Michael, our 30 year old man that weighs 12 Stones and 10lb and is 5ft 10″ tall, runs at a speed of 7.5MPH, then he can get 291 MPG of petrol.
The BBC fuel price calculator thinks that the average UK price of petrol is currently £1.14 a litre.
So for Michael to run his mile, he’ll need to spend a grand total of 1.8 pence
It would cost Michael..
1.8 Pence to run 1 mile.
£14.62 to run from Lands End to John O’Groats (using the preferred Google maps walking route)
£448.22 to run around the world in a straight line on the equator.
It’s already been pointed out to me that it may be a little sexist of me to base these calculations on the assumption that the average human is a male. I think we all know that men will be more likely to drink petrol should the option be available.
Some figures are rounded up/down to make sense… I know that Michael’s BMR is based on him not doing *anything* not even sitting on the couch watching TV.