<P> As soon as the lead leg begins its descent, a strong downward push is exerted to enable the trailing leg's knee to come up under the armpit and in front of the chest . This enables recovery of some of the energy expended in the flight . As the lead leg touches down to the ground, it's critical that the runner remains in a sprint . As soon as his or her lead leg touches down, the trail leg arm drives the rest of the body forward . </P> <P> In the 100 and 110 meter hurdle events, the fastest hurdlers use the three - step technique . This means that three large steps are taken in between all of the hurdles . In order to do this efficiently, hurdlers must take long strides and maintain their speed for the entire race . If a hurdler begins to slow down while three - stepping, they may not be able to make it through all of the hurdles and may have to switch to four - stepping or five - stepping technique . When three - or five - stepping, a hurdler will use the same lead leg for all of the hurdles . If a hurdler four - steps, they will have to switch lead legs at each hurdle . </P> <P> A modern hurdle will fall over if a runner hits it . There is no penalty for hitting a hurdle (provided this is not judged deliberate). The misconception is based on old rules before the hurdles were weighted . In the 1932 Olympics, Bob Tisdall famously won the Olympic Gold medal in the 400 metre hurdles in World Record time, but was not credited with the record due to knocking over a hurdle . There can be disqualification if a hurdler knocks a hurdle into an opponents lane and it is judged to have interfered with the opponent's ability to run the race . There are now specifications for the tipping weight of a hurdle (the weights need to be adjusted to correspond with the height of the hurdle) so hitting a hurdle theoretically slows down the rhythm of the hurdler . However, pushing the hurdle with one's hands or running out of one's lane as a result of hitting the hurdle is cause for disqualification . While hitting hurdles is not generally considered desirable, a few sprint hurdlers have succeeded despite knocking over many hurdles . Contact with hurdles can decrease speed and also result in disruption of a hurdler's technique . Some coaches suggest if you lightly "kiss" the hurdle with the side of the leg closest to the hurdle, it can help with the runners speed by keeping the runner closer to the ground . </P> <P> There are also shuttle hurdle relay races, although they are rarely run . They are usually only found at track meets that consist entirely of relay races . In a shuttle hurdle relay, each of four hurdlers on a team runs the opposite direction from the preceding runner . The standard races correspond to the standard sprint hurdle races: 4 × 110 m for men and 4 × 100 m for women . </P>

What happens when you knock down a hurdle
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