The frequent readers of my blog may wonder whether all of a sudden I have become a race-walking fan. Not to worry! My opinion about race-walking has not changed by a iota. I am still convinced that the discipline is deeply flawed and should either disappear or be radically reformed. Unfortunately WA is just stalling, by discussing about new competitions distances: 10 km and 35 km aiming at replacing the 20 km and 50 km. (By the way the IOC made it clear that the 50 km competition is exiting the Olympics, just when WA was hoping to add the women's race to the program). And of course, there are no news concerning the ground contact sensor which was supposedly been developed and which would have put paid to cheating.
No, in this post of mine I will discuss a point I became aware of while reading an article showcased in the WA weekend reads. The title of the article did capture my curiosity: "Yes, walking is sometimes faster that running uphill". I remember (that was a long time ago when I was still running, before discovering finswimming) having participated at races where there was a steep slope going uphill for more than one kilometre. At that time I was training in a hilly area and thus I had quite some experience in handling steep slopes. But one could observe that most of the participants of the race were just giving up running and were climbing the hill walking. I have always believed that one had some advantage if one could still keep running and this was born out by the fact that the runners I passed were not catching up with me once the steep slope was over. It turns out that things are not so simple.
In some previous post of mine I gave the energetic cost of walking and running. For low velocities walking is more economic but when the velocity increases at a certain point it is more advantageous to run. However these estimates are valid when locomotion takes place on a flat surface. When one starts climbing slopes everything changes. Remember that walking does not involve an aerial phase: one foot is always on the ground. If at a certain point there is no contact with the ground this is running and not walking. Well, things change when it comes to going up a slope. If the slope is steep enough then even running keeps one foot on the ground at all times. You can observe this in the gif below where the subject is running on a 45 degrees inclined treadmill.
(This is really impressive because most mountain runners find it difficult to keep their balance on treadmills with inclinations above 40 degrees). In case you are wondering how can one distinguish walking from running on an inclined treadmill, the answer is given by measuring the acceleration.
As one sees readily in the figure above, walking and running have quite different acceleration patterns. So, how does one choose to walk or run when moving uphill on a steep angle? A recent experiment involved a selection of elite mountain runners who ran and walked on a treadmill during 5 minutes at a time, at angles going from 10 to 40 degrees. The speed of the treadmill was adjusted so that the "vertical" speed was always the same. In practice this means that the treadmill was moving faster for small angles and slower for the steep ones. The measurements of the metabolic cost of the exercise are summarised in the graphic below.
For inclinations up 10 degrees running is more efficient than walking. But once the angle exceeds 15 degrees, walking is more efficient than running. And, for the vertical speed imposed in the experiment, there is an optimum in energy expenditure around 25-30 degrees.
How do these results compare with a real-life situation on mountain running competitions? It turns out that most competitors alternate between running and walking, despite the fact that the latter is more efficient energetically. This can be explained when one considers what is happening on a flat surface. A series of studies have found that the transition walk-to-run occurs at slightly slower-than-expected speeds, although walking is still more efficient energetically. The explanation to this is that certain muscles get fatigued during fast walking and it is more comfortable to run, although this entails a somewhat higher energy expenditure. Comfort is the decisive criterion. In mountain running competition given the slope and the speed of the athlete walking and running correspond to comparable energy expenditures. So, athletes who walk think that they would be more comfortable running and switch, only to get the opposite impression after some time and switch back. There is no preferred style and they oscillate between running and walking, each athlete having his own mix of the two gaits. And what matters in competition is to be as fast as possible, never mind energetic efficiency.
Talking about maximal performance, the question that arises naturally is how does the running records depend on the slope. Kay performed such an analysis and his findings are given below.
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