VO2 Max calculation help..

[Art]

Hi Guys,
I'm doing a fitness course, and trying to understand an exercise in my text book
involving the prediction of a person's volume of Oxygen uptake.
The test is done in an indirect way, predicting V02 Max based on physiological responses to exercise.

The Procedure goes like this:

1. Record the client's weight in kilograms, and record their resting heart rate.

2. Instruct the client to step up and down to a metronome at a rate of 22 steps per minute.

3. Once 3 minutes has elapsed, measure the client's heart rate for 15 seconds, and multiply
that figure by 4, to give a heart rate in BPM (beats per minute).

4. Use the following equation to obtain a predicted V02 Max in l.min-1:


VO2 max (mL.kg-1.min-1) = 65.81 - (0.1847 hr bpm)


Now note that the -1 in the text book is a small "to the power of" style of printing set to
the top right of the character to it's left, just like the 2 in O2 is a small 2 printed to the bottom right of the O.
Also, there is a dot over the V, which I know means it is to be expressed per unit of time. ie. it is a rate.

Now I'm no math guru, but:
1. Why do we measure the client's weight at all?
2. Why do we take resting and working heart rate and only appear to use one?
3. What does this equation mean in English?

Cheers, Art.

 

[Marat]

1) You measure the body weight in order to determine relative VO2, which is what that formula in your 3rd question actually gives you. Without body weight, you can only determine absolute VO2, which comes from finding the amount of oxygen expired and subtracting that from the oxygen inspired.

2) You likely take the resting and work rates in order to make a comparison of the two. This is likely done to determine the affect of body weight on VO2. That's just a guess...but it's a likely explanation.

3)The units of the formula are those for relative V02, however the right side of the equation is a little unorthodox. Do you determine absolute VO2 in your experiment? Normally, you'd find absolute VO2, then convert the liters to mL and divide by the bodyweight. However, i'm guessing that they didnt have you find absolute VO2, and are giving you a short cut method. That said, you probably can't make too much sense out of the equation.

 

[Marat]

Ah, the 4th question in the procedure is asking you to find absolute VO2. Has that term been used in your class? The units for VO2abs are L/min. The formula they are providing for you to determine relative VO2 is very unorthodox though...as the 65.81 looks like a constant...but there is no constant of 65.81. My guess is that 65.81 is the body weight of your subject?

 

[Art]

Say the client's HR in BPM was 114 at the end of the exercise.
I know this is very low.

The right side of the equation: 65.81 - (0.1847 x 114)
is 44.7542.

44.7542 what (in English)?

 

[Marat]

What are the units for 65.81 and 0.1847?

 

[Art]

Thew 65.81 is a constant used in the equation for women.
For men the two constants are different.

 

[Marat]

Ah ok.

The formula tells you the maximum volume of oxygen consumed in mL each minute in relation to the subjects body weight.

It is a measure of the body's ability to effectively use the oxygen that the body takes in during ventilation.

 

[Marat]

44.752 is the volume of oxygen in mL consumed per minute in relation to total body weight


Is that the wording that you are looking for?

 

[Art]

yes, but that result is ridiculous. Is that because the heart rate of 114 BPM after the test is so absurd (it was a rough guess)?

That's 0.00044752 litres per minute?

or is that figure than multiplied by kilograms of body weight to give the absolute value for an individual?

as in... Milliliteres per Kilogram, per minute.

 

[Marat]

Using the formula, you get 44.752 mL/kg/min...which is a normal value after exercise.

To change that to Liters/min you would multiply by the body weight and then divide by 1000.

For example, lets say your subject weighs 70kg. You would take 44.752 ml/kg/min x 70kg = 3,356.4 ml/min . You would then divide that by 1000 which equals 3.3564 L/min

 

[Art]

Ok, that makes sense, thanks

 

[Art]

Ok, so I wrote a calculator for Windows that has a VO2 Max function,
and a 1RM (1 Repetition Max) function as well.

It also works like a normal calculator with big buttons.

RapidShare: Easy Filehosting
MD5: DA31C2EC02DA38315D79FD594751AFBB

Cheers, Art.

 

[Marat]

The calculator itself appears to work as expected.

However, it assumes that absolute VO2 is the same for everyone. It suggests that per minute, everyone inspires and expires the same amount of oxygen. That, of course, is not the case.
Additionally, it holds that the only factor that affects relative VO2 max is one's bodyweight. In order to find relative VO2 max, you need to know the volume of expired and inspired air at STPD as well as the bodyweight of the individual. The calculator appears to hold that the absolute VO2 is equal for everyone, and only accounts for bodyweight. Is that the case?

If so, it is like saying that because I may weigh less than you, that I can run a lap in my gym faster than you can in your gym. However, you are ignoring the length of the two tracks that we may be running on.

 

[Art]

If I've used the method posted above, is the calculator any more flawed than this method?

Should I remove the step of multiplying by bodyweight and dividing by 1000?

 

[Art]

The readme of the calculator details the exercise in the first post,
so everyone should have stepped at a certain rate for exactly three minutes.
the exact volume of air inspired and expired couldn't be considered in a gym fit test of course.

Also from first post:

The test is done in an indirect way, predicting V02 Max based on physiological responses to exercise.

I understand that cannot be a direct measurement of VO2 Max in a gym environment because
we can't measure the oxygen volume on the way in and out of the lungs.

Given this, is the calculator a reasonable representation of the method described in the first post?
I plan to submit the finished calculator for assessment for units of the course in computer literacy and fitness testing.

 

[Marat]

Oh I apologize. I didn't read the Read Me.

That said, the calculator does work properly. Good work

 

[Art]

Good... well, thanks again for the help with it.