In terms of total energy expenditure is it more expensive running a 10 km race at 10 km/h or at 20 km/h? If we don't consider the air friction component and if the race is run without any pace variation (steady state), the answer is: the total energy requirement is approximately the same!
The reason lies in the linear relationship between oxygen consumption and running speed. As a rule of thumb, during horizontal running the energy cost is about 1 kCal/kg/km. Thus, the energy cost of running 10 km for a 70 kg individual averages 700 kCal, regardless of running speed.
Having an ergospirometer, as explained in the previous Part 1 and Part 2, allows to know the relative contribution of Carbohydrates and Lipids in the energy transfer system; in Figure 1 the data are put together in a graph, and the main results can be described as follows:
the whole-body energy requirement increases up to 15-20 times above resting levels (purple curve);
for this athlete, between 6 and 10 km/h is evident the formation of a plateau where the ratio between Fats and Carbs contribution is constant;
training to extend the plateau is something to focus on, since the energy contribution of Fats is more than double of the Carbs' one (9 kCal/g vs. 4 kCal/g);
the higher the speed, the lower the Fat's contribution;
training at low speeds is a good way to "teach" the body to use the Lipids as energy source;
doing a Conconi test will allow the athlete to know exactly the different "fuels" contribution at his anaerobic threshold;
Proteins contribution is not taken into account, as explained in the Part 2.
Figure 1 - Energy expenditure during running.
We are working on the fourth part, wich will be published after the next test session. Meanwhile...keep on training, people!
Here you can find a list of my running-related posts. Now shut down the notebook and have a run!