100 METRES

The record run is not animated by hand. His distance at every instant is a smooth monotone curve through the ten official split times, reaction included; his speed is that curve's slope, so it reaches about 12.3 m/s between 60 and 70 m; his legs turn over at speed divided by a step length scaled so the race takes his real 41 steps.

Simplified: the figures are stylised, the step-length curve is a smooth fit rather than a measurement of each step, and the slow-down after the line is invented. The race clock starts on the frame the flash is drawn and stops at your tap's own timestamp, so your screen and your touch hardware are inside the number. The average adult is an illustrative profile, not data.

• Splits, reaction time and step count of the 9.58. Graubner, R. & Nixdorf, E. (2011). Biomechanical analysis of the sprint and hurdles events at the 2009 IAAF World Championships in Athletics. New Studies in Athletics 26(1/2), 19–53.
• False start below 0.100 s. World Athletics Technical Rules, TR 16.6 (start information systems).
• Reaction times under 0.100 s in trained sprinters. Pain, M.T.G. & Hibbs, A. (2007). Sprint starts and the minimum auditory reaction time. Journal of Sports Sciences 25(1), 79–86.
• The previous record, 9.69. Beijing Olympic Games final, 16 August 2008 (World Athletics records).
• Photo finish. World Athletics Technical Rules, TR 19 (fully automatic timing and photo finish).