I know most running bloggers maintain personal blogs, in other words they write in a diary style and their purpose isn't to attract a bunch of readers from Google. I also fit somewhat into this category, except for that I do like organic traffic. Once I turn 18, I plan on adding Adsense to this blog (in a very unintrusive manner, sort of like on this running blog). So don't worry about being spammed with obnoxious advertisements in the near future.
Anyways, as those who are in the know about SEO (search engine optimization) are very aware, one of the most important factors for getting a high page rank in google (how high your site will appear in a search for a given key term) is backlinks. I'm not going to go into a ton of detail - this isn't an SEO blog, but I will give those who don't understand a bit of background information. Backlinks are one-way links on other websites that lead to your site. Google uses them as a measure of a site's popularity, and indexes accordingly.
But that's not all there is to it. One of the keys to getting a backlink to be more effective and actually make a difference in Google's eyes is for it to be coming from a relevant site. For example, if I got a backlink from a cooking blog, it wouldn't help me very much as my blog is about running. A backlink from another running blog would be much more beneficial to me in terms of page rank.
One more thing - the blog you get a backlink on through commenting must be dofollow. Blogspot blogs by default are nofollow, meaning that links in the comments section aren't taken into account by Google crawlers (bots that find and count backlinks). So the following is a list of running/exercise blogs that are dofollow, sorted by page rank (backlinks from higher PR sites are given more weight by Google).
Page Rank of 4:
Justin Wright: Exploring Life After the Cubicle
Page Rank of 3:
Page Rank of 2:
Run the Line
Page Rank of 0:
Running and Fundraising
...The list isn't big yet but its growing! If you have any dofollow, relevant blogs in mind, please share!