TheETG applied sport sciences
“The energy cost of overcoming air resistance on a calm day outdoor was calculated to be 7.8% for sprinting, 4% middle-distance, and 2% marathon running.”

C.T. Davies
Effects of wind assistance and resistance on the forward motion of a runner.
Journal of Applied Physiology…….Volume 48 #4……April 1980…….page 702 – 709

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“…..the external work done per unit time against air resistance is about 7.5 – 9% of the total power output of a sprinter, running at maximum speed at sea level. These figures compare well with the value of 7.8% obtained independently by Davies (J. appl. Physiol 48, 702-709, 1980).”

A.J.Ward-Smith
Air Resistance And Its Influence On The Biomechanics And Energetics Of Sprinting At Sea Level And At Altitude.
Journal of biomechanics……Volume 17 #5……1984……page 339 – 347