It is
difficult to make the direct measurement of power output, and thus the amount of
calories burned while jogging or running, but it is
much easier to estimate. Although the bike is much more friendly when it comes
to measuring the efficiency, power output and calories, but it is also possible in running or
jogging. Today, I will suggest one of mathematical methods to perform such
measurements, and also consider the implications of the calculated numbers.
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| Burning calories when running |
The method of measuring the number of burned calories while running.
We know that heart rate reflects the
output power and mimics it in the linear fashion in the wide range of aerobic
exercise under lactate threshold. This means that if the pulse increases, power
increases accordingly. Another well-known dependence in running, combines
running speed and pulse. This, fortunately is also linear. If both of these
equations have a common variable, which is the pulse, we can completely get rid of
it in the calculations.
This leaves us with the final
equation, combining the speed linearly with power, for a person of a given
weight. Body weight is the most important factor, so it must be taken into
consideration, when estimating. All given dependencies well characterize
running on a flat terrain.
Unfortunately, the reality is not two dimensional, knowing the race route we should take into account uphill and
downhill movement as well. These result into changes of potential energy, so
requires power. We can use simple equations known from high school physics,
modified by specific factors related to the economy of human exercise.
Knowing the power of running, we also know the amount of calories burned.
Mechanical power is the basis
of human energy expenditure estimation. Skeletal muscles are rather
inefficient, and the whole body is wasting a lot of energy. Thus, the estimated
mechanical power is only a small percentage of total energy expenditure, which
more than four times higher. A lot depends on weather conditions, running
economy, associated with cross-country running, runner outfit, type of shoes and the kind of terrain on which we
run.
We know that a kilogram of body fat (80% of triglycerides), contains about
7000kcal. Normally during exercise, the fat is not the only thing, that is
burned. This makes the fat provide only a certain percentage of fuel, which is
the source of power in our body, while running. The body depleting the energy
resources will also be trying to increase the appetite, making it difficult for
any weight loss (see the article running and weight loss shortly).
Let's try the sample data from
the authors training, to see how much fat body mass, he managed to burn during
exercise and how much would he have to run to, to burn 1 kg with the speed he
normally runs.
An example from the real life.
My sample was characterized by
the distance run 4km in rather flat terrain of the forest area of Lodz, Poland. I managed to achieve an average speed of 8.7 km/h, while
the median of the motion was 9km/h (median is usually better in estimating some
features, than the average with real-world examples of long term exercise like running ), and exercise time
was half an hour. I estimated the average power to 100 W, which gives about 160
calories burned during this training session, because the body has a tendency
to waste many times more than the actual mechanical power.
According
to these data, one hour of running with low/medium intensity allows you to
burn about 350kcal of energy, equivalent to the energy derived from a single
hamburger. One kilogram of body fat is burned during the 20 hours of such exercise
with no additional energy supply, but at medium intensity.
The researchers examined
ultramarathon runners who covered hundreds of kilometers with high intensity,
using isotonic drimks, nutrition and supplementation during the
race. Ultramarathon running on time completion of 48 - 58 hours, results in about 3
kg body fat decrease, so 21 000 000 calories (21 000 kcal) are burned. This
is within reasonable agreement with our mathematical estimations.
