Actually steroids & running go perfectly together. Not dbol. But yeah running wrecks havoc on Fast Twitch (red), muscle fiber......but test actually helps it rebuild & if a person runs a lot......one can actually make fast twitch act like slow twitch. Plus.....I disagree.....I'll find the article that showed the study that mitachondria (slow twitch), does grow & accounts for a smaller percentage of total size of the body builder. Next thing I disagree with is all muscle.....not just slow twitch learn to utilize nutrients & energy better in training.
As for the skinny runner......hehehehe if they start eating like a body builder they would not be so stringy.....they try to stay that way because it's hard to carry that for a long distance, though the bigger guys may never win a marathon.......I've seen long distance runners with monstrous legs.