Hurdle races

Worked example 1: does the three-stride rhythm fit? Mugisha (U18) runs the 110 m hurdles. In training he takes off 2.0 m before each hurdle and lands 1.2 m after it. How long must each of his three strides between hurdles be?

1. Hurdle stride: $2.0+1.2=3.2\mathrm{m}2.0\; +\; 1.2\; =\; 3.2\backslash ,\backslash mathrm\{m\}$.
2. Distance left for the running strides: $9.14-3.2=5.94\mathrm{m}9.14\; -\; 3.2\; =\; 5.94\backslash ,\backslash mathrm\{m\}$.
3. Each of the three strides: $\frac{5.94}{3}=1.98\mathrm{m}\backslash frac\{5.94\}\{3\}\; =\; 1.98\backslash ,\backslash mathrm\{m\}$.

A stride of about 2 m is realistic for a fast U18 sprinter, so three strides fit. A pupil whose natural stride at that speed is only 1.6 m would need $\frac{5.94}{1.6}\approx 3.7\backslash frac\{5.94\}\{1.6\}\; \backslash approx\; 3.7$ strides: too many for three and too few for five. For such pupils teachers use shorter spacings and lower hurdles in training, so that the rhythm can be learned before the full distances.

Worked example 2: odd and even strides in the 400 m hurdles. Between 400 m hurdles there are 35 m. Take the hurdle stride as about 3.5 m.

1. Running distance: $35-3.5=31.5\mathrm{m}35\; -\; 3.5\; =\; 31.5\backslash ,\backslash mathrm\{m\}$.
2. With 15 strides, each is $\frac{31.5}{15}=2.10\mathrm{m}\backslash frac\{31.5\}\{15\}\; =\; 2.10\backslash ,\backslash mathrm\{m\}$; with 14 strides, $\frac{31.5}{14}=2.25\mathrm{m}\backslash frac\{31.5\}\{14\}\; =\; 2.25\backslash ,\backslash mathrm\{m\}$.

Landing is always on the lead leg. With an odd number of strides (3, 13, 15), the take-off is again from the trail leg, so the athlete leads with the same leg every time. With an even number (14), the take-off foot changes, so the athlete must lead with the other leg at the next hurdle. That is why 400 m hurdlers practise leading with both legs: as they tire on the final bend, their strides shorten and they often change from 15 to 16 or 17 strides.