I aslo bought that book about 6 years ago.
I even tried the exercises, and they were useless, and yes, I had a slight decrease in my sprinting speed.
Michael Yessis believes you can train each individual element of the sprint stride with stretch bands and cables.
He’s wrong. He has studied bio-mechanics and kienesology, but has a useless training method. He has worked with athletes from other sports such as tennis. The sprinters featured in his book, all looked second rate.
In one photo, he demonstrates halfsquats (not even as deep as parrallel) with nothing more than a stretch band tied to his waist, and the other ends under his feet.
The only chapter that is interesting, was the chapter on bare-foot running. Bare-foot running is an interesting training option for middle distance cross-country runners and recreational runners, but I don’t see how it is practical for sprinters. Apart from may be in the warm up and cool down phases of a training session, done on the in-field.