How to convert relative to absolute VO2 values

My name is Sarah Wilkinson.

This is the second of the video series

showing how to convert VO2 values.

In this video I am going to show you how to

easily convert a relative VO2 value to an

absolute VO2 value.

Please make sure you have watched the first video

which shows you the basic mathematical principle

I am using to do these conversion factors.

As a well as a little background of what VO2 is.

In this video I am going to show you how to

convert a relative VO2 value,

which is measured in ml per kg body mass per minute

to an absolute value, in litres per minute.

I am going to set it up by putting
my relative value on the left hand side

and on the far right hand side, I have put in

what I am trying to convert to,

so the absolute value of L per minute.

Let's use a theoretical example, and say we have

someone with a VO2max of

45 ml of oxygen per kilogram body mass
per minute

This is essentially 45 ml per 1kg minute.

Normally we don't put the '1' in.

Just to show you what should be on the denominator.

I need to do two conversions factors.

I need to convert millilitres to litres

minutes will remain, but I
need to remove kilograms.

For some people, whether to divide or multiply by 1000

and divide or multiply the the body mass becomes

a little confusing.

So setting up in this manner helps you decide

whether you need to divide or multiply.

Again the principle I am using,

is that if one unit is on the numerator,
for this example 'ml'

I can multiply by a conversion factor and put
the 'ml' on the denominator in the conversion factor,

and those two will cancel out.

We know how how many millilitres are in 1 litre.

That is what we are trying to convert to here.

There is 1000 ml in 1 L.

If I stopped at this point, by cancelling out 'ml'

I would take 45 and divide by 1000.

However, if I stopped at this point,

I would end up with litres per kilogram per minute

Remember an absolute value is measured in L/min.

Therefore, I must also "get rid" of the kilograms.

So I need to either divide or multiply by kg.

For some people, what to do may be clear to you.

For others, not so much.

We are going to use the same principle again.

We need to "remove" kg in the next conversion factor.

And it is on the denominator, on the left hand side.

In order to cancel it out, I need to put is on the numerator.

Remember top is going to cancel out bottom.

Let's say for this example, the person is 78 kg.

And again that is over '1'.

'kg' will cancel each other out.

Top cancels out bottom.

To finish this off, all I need to do, is multiply all

numbers together and
divide by all the bottom numbers.

Because anything divided or multiplied by one

is one, I am going to worry about the numbers

that are not one.

I am going to take 45 and multiply it by 78

and divide by 1000.

This gives me the answer of 3.51 litres per 1 min.

In this example, I have converted a relative VO2max

of 45 ml per kg per minute and converted it

to an absolute value of 3.51 litres per minute.

Let's do another example now.

I want you to convert Stanley's relative
VO2 of 30 ml per kg per minute

to an absolute VO2 value in L/min.

His body mass is 80 kg.

Please pause this video now.
Try this out on your own.

Once you have come up with the answer,
or if you get stuck, press play again.

Again we are converting a relative value in ml per kg per min.

to an absolute value, in L/min.

Stanley's relative value is 30 ml per 1 kg minute

We want to convert ml to L.

We set it up so that the numerator
cancels out the denominator.

We know there is 1000 ml per 1 L.

'ml' cancel out.

We need to multiply by kg because

in the relative value it is on the denominator.

We need to kg on the numerator.

And we know Stanley is 80 kg.

'kg' cancel out.

In this example, I am going to take

30 multiplied by 80 and divide by 1000

to get my absolute value of 2.4 L/min.