The old adage is that one can't coach speed. It is a natural gift. It seems now that that old adage is somewhat modified. One can't coach speed but one can improve it chemically.
In the latest edition of Annals of Internal Medicine (2010; 152: 568-577), there is a published study of a randomized placebo control blinded study looking at growth hormone alone and in combination with testosterone. Guess what, those taking growth hormone alone had improved sprint capacity (a measure of power and anaerobic performance). those taking both growth hormone and testosterone show even greater increase in sprint capacity.
As of now, growth hormone can't be detected. Testosterone can be detected.
Now the funny part is the editors, supposedly very smart folks, commented that, “The athletic significance of the change in sprint capacity is unknown.†So if one can have more power for long, the editors haven’t a clue whether that is important or not.
Wish growth hormone was around back in the day.