Wednesday, August 20, 2008
Usain Bolt’s gold-medal-winning and world-record-setting 9.69-second performance over 100 meters at the Beijing Olympics was an astonishing surge of “running lightning.” Let’s take a look at how he accomplished it.
In contrast to the other sprinters in the race, who took about 44 steps to cover the 100-meter distance, Usain required only 41 steps. His step length averaged 100/41 = 2.44 meters per step. Everyone else hovered around 100/44 = 2.27 meters per step, a 7-percent diminishment (compared to Usain). It’s tempting to say that Usain won the race because of his long strides.
But hold on a minute: Step length is a function of the force placed on the ground during each contact, but it is also a variable which depends on height – longer limbs naturally lead to more-expansive strides. Usain stands 6’ 5”, according to media reports, or about 1.96 meters. The third-place finisher in the Beijing 100, Walter Dix, is only 5’ 9”, or 1.75 meters.
Among well-trained distance runners who are competing in a 5- or 10-K race, step length averages about 1.03 times height. You can readily see that things are quite different in the world of elite sprinting. During the Olympic-final 100, Usain’s relative step length was 2.44/1.96 = 1.24 times height. Walter’s relative step length was 2.27/1.75 = 1.30 times height.
Oops! We can see that Usain did not win the race because of his extraordinarily long strides. In fact, his steps were relatively shorter than Walter Dix’s, when expressed in relation to height.
What else might have accounted for Usain’s astounding speed? Actual velocity in a race is a function of just two things – step length and step rate, so let’s compared the step rates of Walter and Usain (we already know that Usain had a longer absolute step length and a shorter relative step length). Walter finished the race in 9.91 seconds to get his bronze medal, and so his step rate was 44/9.91 = 4.44 steps per second. Step rate is usually expressed in steps per minute, even when a race lasts less than one-sixth of a minute (like this Olympic final), so let’s figure Walter’s step rate that way: 4.44 steps per second X 60 seconds per minute = 266.4 steps per minute. That’s putting them down on the ground!
Usain’s step rate was 41/9.69 = 4.23 steps per second. Bringing that figure up to standard, we have 4.23 X 60 = 254 steps per minute. He was laying them down, too, but his step rate was actually 4.7-percent lower than Walter’s.
And thus we can see the fundamental nature of the competition between the two men. Usain covered more absolute ground with each step, so Walter had to try to make up for that by making more steps per second. He worked valiantly – and ran so explosively that Usain’s step rate was 4.7-percent smaller than his.
If step length had been equal – or in fact if Usain had managed less than a 4.7-percent advantage in step length over Walter, the race would have gone to the little fellow. Walter’s problem was that Usain’s step lengths were 7-percent broader. From elementary school math, we know that 7 minus 4.7 = 2.3 (here, we are simply subtracting 4.7, Walter’s advantage in step rate, from 7, Usain’s edge in step length). And 2.3 percent was almost the exact margin of difference between Walter and Usain (.023 X 9.91 = .228 seconds, just a whisker above the actual .22-second disparity).
If Walter had boosted his step length by “just” 2.4 percent (greater than the 2.3-percent difference between the two men), he would have won the race. However, bear in mind that an elongation of step length might have hurt Walter’s step rate (because more time would have been needed on the ground to generate the force necessary to fly farther between steps). Most importantly, during very high-speed running a runner reaches his/her limit on step length before reaching his/her limit on step rate. In other words, beyond a certain point (as a runner gets closer and closer to max speed), further increases in velocity can only be accomplished by upping step rate, not by boosting step length. Thus, it’s very likely that Walter could not have augmented step length by even .1 percent and maintained his 10.09 meters per second velocity (100/9.91).
The bottom line? Usain won the race not because of his extraordinarily long steps, which were actually less impressive than Walter’s, taking height into account. He won despite having a lower relative step length and a slower step rate. The key was that the difference in absolute step lengths between Usain and Walter (a “plus” for Usain) was greater than the disparity in step rates (a “minus” for the gold-medal winner). Putting it another way, Usain had optimized his combination of step length and rate, producing a lightning-Bolt of astonishing running.
This begs the questions: How can endurance runners optimize step length and step rate and thus become intrinsically faster runners? This is important not just for “kicking” at the ends of races: Scientific research has revealed that 50- and 300-meter sprint times do a better job of predicting 10-K performance than VO2max (maximal aerobic capacity). In an upcoming series of articles on this blog, we’ll cover the training strategies which are best for upgrading stride length and rate – and thus for making you a much-more-successful (and “better-educated” runner).