Davies found that when a runner was measured on the treadmill, facing winds of up to 18 km/hr had no effect on the oxygen cost of running. But the same conditions on the road will have a very marked effect. On the treadmill, the athlete does not move forward and thus does not expend energy overcoming air resistance. However, an athlete who runs on the road into a wind of 18 km/hr faces an actual wind speed equal to that of his or her running speed plus that of the prevailing wind.
The practical relevance of this is that on a calm day, anyone running slower than 18 km/hr (about a 2:21 marathon pace) will not benefit by drafting in the wake of other runners. However, runners stand to gain considerably by drafting when running at faster speeds or when running into winds that, when added to their running speeds, would make the actual wind speed greater than 18 km/hr.
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Of course, the world marathon record is run at a faster pace than 18 km/hr. This means that athletes intent on setting world marathon records would be well advised to draft for as much of the race as possible. Front running in the marathon is almost as wasteful of energy as is front running on the track. One can only assume that as runners begin to realize this fact, we shall see pacers in marathon races just as we now have them in track races.
The only way besides drafting to reduce wind resistance is to run with a following wind, the speed of which is at least equal to that of the runner. Davies calculated that under these circumstances, the removal of the energy required to overcome wind resistance at world marathon pace (19.91 km/hr) would increase the runner’s speed by about 0.82 km/hr, equivalent to a reduction in racing time of about 5 minutes. Similarly, drafting in a tightly knit bunch for the entire race would reduce air resistance by about 80%, allowing the runner to run about 4 minutes faster.
Davies found that the effect of a tail wind on the oxygen cost of running was about half that of a facing wind (although obviously this effect was to the runner’s advantage). Thus, a following wind of 19.8 km/hr is of little assistance to runners running slower than 18 km/hr, but a following wind of 19.8 km/hr would assist a world marathon record attempt to the extent of a 0.5-km/hr increase in speed. Higher following wind speeds of 35 to 66 km/hr would improve running speeds by 1.5 to 4 km/hr.