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Usain Bolt showed his dominance of men's sprinting at the athletics World Championship in Beijing this week with wins in the 100m and 200m. What's his secret? Is the way to win at sprinting to move your legs faster than your rivals do?

Since the Beijing Olympics in 2008 Bolt has won every race he's entered at a World Championship or the Olympics, with the exception of one, where he was disqualified for making a false start.
When non-athletes want to run fast they set about moving their legs as fast as they can, so you might assume that Bolt has achieved this exceptional record by making his legs move faster than everyone else has. But this idea doesn't stand up - in fact, it falls flat on its face.

"Elite sprinters don't swing their legs any faster than recreational runners," says Dr Sam Allen of Loughborough University.
Instead, the difference is that a top sprinter takes longer and more powerful strides.

Research shows that an amateur runner often takes between 50 and 55 steps to complete 100m, while an elite sprinter takes in the region of 45.