Aaberg's formula for calculating how many calories you burn (c:

Aaberg said:

I have a theory on how to accurately calculate your calorie expenditure during exercise below lactate threshold.

Anyone who wants to confirm/challenge the following reasoning:

Lets say I tested my VO2max in a laboratory test and found that:

Weight= 70kg
VO2max relative = 50ml/kg/min
VO2max absolute = 3.5L/min
HRmax (at which VO2max was measured) = 200bpm

When I divide the 3.5 litres of oxygen pumped out by my heart every minute by 200bpm, I find that my heart pumps 17.5ml of oxygen for every heart stroke.

Suppose I am exercising below lactate threshold (I am working mostly aerobic), lets say at 150bpm, for one hour. This means my heart is pumping out:

150bpm x 17.5ml/beat = 2.625 litres of oxygen every minute.
This equals 2.625 x 60 = 157.5 litres of oxygen every hour.

1 liter of oxygen produces 4.6-5.0kcal, depending on the proportions of glycogen and fat beeing used as fuel.

For my example, this means that the energy production is somewhere between:

157.5 litres x 4.6kcal/L = 724.5kcal and
157.5 litres x 5.0kcal/L = 787.5kcal.

I know that heart stroke volume increase as HR increase, so that may influence the results to a certain degree (at 150bpm I would be pumping a little less than 17.5ml per stroke).

So... is this reasoning valid?

If it is, all you have to know is your VO2max and you can easily approximate your own energy expenditure from your average HR after a ride, possibly more accurate than your power meter, HR monitor, etc.

_______
Aaberg

Only two objections...

a) Relationship between HR and VO2 comsumption is not linear. That means
that a % of your HRMax doesn't match a % of your VO2 max.
b) Relationship between Power Output and HR is not linear (Conconi test).
The rate of power incresed per HR unit is different above LT and below...

So I guess there are two zones where you can apply the relationship with
different O2 (and hence calories) per HeartBeat: Above and Below Threshold.

Anyways... theres is a formula (or lots of different ones.. 😄 ) that ties
VO2 consumption (as a % of VO2Max) with HR (as a % of VO2Max). And as said, It is not linear. But If you use that formula you can go from VO2Max
calorie/hour consumption, work out at what % of VO2Max you are working
given a Heart Rate, and the work out the calories. This is the way. There
are lots of applets/javascripts that relates HR and VO2, so... you have it at your fingertips 😄

Cheers!!