A dirty little secret here: There is research showing that 20% improvement in squat strength translates into a 2% improvement in 40m sprint. It does transfer if you're a distance runner, but it doesn't transfer if you're a sprinter, and that's the opposite of what many coaches think. To what extent are American and Jamaican sprinters testing positive so they can add something that they believe works but actually doesn't do jack unless you're a beginner?
Evidence:
--Usain Bolt. In 2008-2009 he was more like 195 pounds. Everybody said that when he lifts more weights and grows into his body, he will get faster. He's now a more muscular 207. He's also slower.
--Kim Collins. The Lagat of sprinting. He does do weights now (didn't until the last few years), but still VERY skinny by modern standards.
--Jimmy Vicaut. He's about the same build are Armin Hary.
--Francis Obikwelu. Something like 6'5"/165, built like Johnny Gray. He finished with the silver in 2004 (9.85, as I recall), AHEAD or Maurice Greene.
--Marion Jones. Not skinny, but what's interesting is that her PRs were set in 1998, BEFORE she married CJ Hunter and BEFORE she trained with Trevor Graham. It is believed that she started doping in the buildup for the 2000 Olympics, and she kept both her PRs and her 1997 and 1999 world championships. It appears that she took steroids and GOT SLOWER.
I'm not saying to do zero weights, but the correlation is questionable, to say the least. There is very little scientific evidence of weight training doing much for sprinters. And the reason you don't see many skinny sprinters is because they believe they need to get big, not because it actually makes you faster.