sub 20 min 5k (Read 2539 times)

If you run at a steady pace, your heart rate will always creep upward, no matter what the pace. This is called "cardiac drift." The faster the pace, the more it drifts upward, but even at an "easy" pace, it will always climb over the course of a run. This is why you have to slow down as you go in order to maintain a given target heart rate, as in these MAF tests. And that's one reason why I don't think that I personally could run like this. On non-speed days (which is every day these days due to my strained calf and the hot weather), I prefer to run at a steady pace, and maybe finish slightly faster, just to keep used to the idea of steady pacing / negative splits when it comes time to race. I don't enjoy slowing down as I go. I do think that there's plenty of merit to some aspects of the MAF training, particularly the idea of keeping easy days easy and aerobic base-building. I had a coach who told me no speedwork until you're up to at least 40~45 miles per week, and it was because he wanted me to build a sufficient aerobic base. My MAF target is 149 bpm. On most of my easy days, my average heart rate over the course of a run is around 151. I figure, given that cardiac drift is a given, if my average HR for the run is close to MAF, then it's been sufficiently easy. I'm not going to fight cardiac drift and slow down as I go. Mind you, I'm not being a contrarian about aerobic base building or MAF training -- I just prefer to run a steady pace by feel and to not worry about feeling the need to decrease my speed as I go. But I still keep on eye on HR on easy days just to be sure they stay easy.

I don't enjoy slowing down as I go.

There's an alternative to slowing down. Choose your pace so that your heart rate starts out lower than your limit, and only approaches the limit as it drifts upward near the end of your workout. Anyway, at this point I don't experience a lot of drift. It's only really noticeable to me on runs over 10 miles, or in very hot weather.

Here's a followup on heart rate drift. Today I did a 10.9 mile run at my usual 145 heart rate. I took splits at a few known landmarks: First 2 miles -- 9:18 pace (avg HR only 134 due to slowly warming up) 2 mi to 4.7 mi -- 9:10 pace 4.7 mi to 8.9 mi -- 9:11 pace 8.9 mi to 10.9 mi -- 9:26 pace So you can see that my drift is pretty minor, and doesn't really become noticeable until after 9 miles. In comparison, a month ago my pace drifted from around 9:00 to over 10:00 on this same course.