It is that time of year when parents start calling for "speed training". The first thing I am told is they don't want little Johnny or Mary to become "muscle bound", they just want them to be faster, more agile.
sprinter long distance runner
There is a reason sprinters, and jumpers have muscles, it is because you must first have strength before you produce power, or speed. Speed is basically strength produced quickly, with out one you can't have the other.
That being said, it isn't necessary to make little Mary look like a football player, but it is necessary for her to be somewhat stronger before she is going to get any faster.