Measuring Calories Burned when Jogging or Running

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.

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.