World-class athletes of both sexes cover 100 metres in about 10 seconds. What percentage of this is spent not touching the ground? And what’s the figure for a 2-hour marathon?
• Every step can be broken into two parts: ground contact time and flight time. As people run faster, the time they spend in contact with the ground decreases, but so too does the time between steps. This means the relationship between the two parts doesn’t necessarily change.
The current world record for 100 metres is Usain Bolt’s 9.58 seconds, meaning an average speed of 10.4 metres per second. Research has estimated his ground contact time to be 91 milliseconds and his step time to be 236 milliseconds. He typically covers 100 metres in 41 steps, spending 39 per cent of the race touching the ground.
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In September 2018, Eliud Kipchoge set a new marathon record of 2 hours, 1 minute and 39 seconds. His average speed was 5.8 metres per second, and ground contact time at this speed is 110 to 130 milliseconds. Assuming a figure of 120 milliseconds and Kipchoge taking around 25,000 steps, his feet spent about 41 per cent of the race on the ground.
The higher percentage is partly due to differences in how runners land: sprinters do so on the balls of their feet, rarely allowing their heels to touch the ground. In contrast, the heels of even highly trained runners tend to drop during marathons due to fatigue.
It is worth noting, however, the relatively small difference in ground contact times (39 to 41 per cent), highlighting the very high level of training of these athletes.
Laura-Anne Furlong, Lecturer in biomechanics, University of Loughborough, UK
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