Anaerobic Threshold

So I'm studying quite a bit about anaerobic threshold training for distance runners. My understanding is that you can improve your time significantly (like more than a minute per mile for novice runner's.) I wonder if anyone has looked into this or knows anything about it? My curiosity is officially peaked!

Good Run

It's amazing to me that I can have a really painful, overwhelming run one week, and then the next week increase my miles and have a great run, pain free. So, I suppose the takeaway message here, is that I need to keep myself 'mentally' Succeeding regardless of what my body is doing. I'm a big believer in positive affirmations. Although, I still find myself wondering how I will be able to get to 26.2 miles. Whew! I guess I shouldn't think about it yet.

Pain :/

O.K. so between running with my hubs (and trying to keep up with him!) and weightlifting. I think I overdid it a little this week. I also increased miles. First time I have ever had what feels like shin splints. So, this brings up a good question. How can you tell the difference between O.K. pain (the kind that is good for increasing muscle mass) and injury pain?