Thursday, April 23, 2009

Aerobic Conditioning

In my blog yesterday I made a snide comment about speed work: "I am quite amused by the people running 15 to 20 miles per week who think that they will run a faster half marathon times by introducing speed work." I received a couple of comments, a few emails, and a couple of tweets about this comment, so I thought I would explain myself.

First, I apologize to all you teachers out there. " a faster half marathon times..." Anyone have a red pencil? Time to read before posting. Yow!

Next - the real purpose of the statement. Everyday I spend some time cruising the forums over at Runner's World and reading a bunch of running related blogs (see the sidebar). There are always tons of questions about speed work. "When should I start speed work?" "I want to add speed work to my training plan." "I think I should start doing speed work." So on and so forth. Here's the bottom line. It doesn't matter how much speed work you do in a training cycle. If you run out of gas before your race is done, you are in trouble.

Performance is greatly dependent on our muscles' ability to use oxygen to produce energy. This is the "aerobic" cycle. Once they reach their upper limit, our muscles quickly start breaking down glucose without the use of oxygen . This is the "anaerobic" cycle. This cycle produces acidic byproducts. If we produce acid faster than we can flush it out, we end up with rapid muscle fatigue. We have just run out of gas.

The key here for any distance is to be able to run aerobically as long as possible. According to Glover, energy needs for marathon and half marathon distances are met 99% aerobically and 1% anaerobically. Even at 10K distances, energy is 97% aerobic. Skew your anaerobic metabolism a couple of percent and you will not be able to perform at your max. We typically manage this by proper race pacing. In essence all that proper race pacing does is slows us down so we don't drive our metabolism out of our aerobic zone.

Hopefully, you are getting the gist of this message. Want to run faster farther? Be more aerobically fit. Want to be more aerobically fit? Run more general aerobic miles. Now, that doesn't mean that speed work doesn't play a part. What speed work does is allows us to buffer acid buildup, which allows us to run anaerobically a little longer. But the real key is to be able to run aerobically for a longer period of time. Once you figure that out, you will watch your times plummet!

I speak from experience. Since increasing my mileage base from 20 to 30+ miles per week during the last nine months, I've seen the following improvements: 5K PR - dropped almost 3 minutes; 10K PR - dropped 6 minutes; Half Marathon - dropped 6 minutes; Marathon - to be determined. This means that I am adequately trained at the 10K distance. I still have trouble at the Half (out beyond mile 11), and I have yet to run a marathon since upping my mileage. I'll get a better feel for my Half in a couple of weeks. And Marathon - well, you'll just have to wait a while!

Sorry for the long post. Oh yeah - I did run yesterday. Six miles, general aerobic (heart rate 80% of max) at an average pace of 9:22. On tap today - 60 minute tempo run. This will be a challenge for sure!


  1. Ok. I must not have had my Red Pencil English eyes on my head.

    Run farter, faster huh? Don't you know that hills are really speedwork in disguise? (Not my quote, but I like it.)

  2. hey i agreed with you. no reason to incorporate speed work until you have a decent base built. your pr's and improvement are awesome!