Thursday, May 26, 2011

Running by the numbers

After the end of winter track season, I took my mileage down under 60 for two weeks, and I didn't do any workouts. During this period, something strange happened: I would run just like normal on my standard running loops, and I would return home two or three minutes earlier than usual. My training pace, which had been around 7:30-7:45, was suddenly down around 7:10 pace.

I was thrilled! All that hard work was paying off! My coach was not as thrilled:
Just because you CAN run faster doesn't mean you should... If you'd like to be more scientific about it, we can get you set up with a heart rate monitor with target zones, but I think you'll work out and most importantly race better if you're a bit more relaxed on "off" days.

Get all scientific about it? Say no more; I'm on it! I got out the heart rate monitor and, since March 1, I have been recording my average heart rate for as many runs as possible. I've been graphing HR vs. pace as I go along:

I know this is hard to read. Sorry. You can view the full size. The trend is clear: As the pace slows down, the heart rate comes down.

It is a fact that if you run at a constant speed, your heart rate will slowly increase. So for a given pace, the average heart rate will tend to be higher for a 10-mile run than for a five-mile run. Because of this, I labeled each data point with the run's distance.

This graph contains many stories. There is the hilly 13-miler that I slogged through with a heart rate averaging 159 (bordering on "tempo effort"). On the other hand, there's a smooth 8-mile run averaging under 7:30 pace but with my heart rate at a cool 142.

I now have a better sense of what my heart rate is when I'm running; I can sometimes guess what it's going to be, without looking. If I'm running along and I don't feel very good, I'll glance down -- "oh, heart rate is 157, maybe that's why."

Something unexpected: My team does the same loop for both warm-up and cool-down on workout days, but my heart rate is drastically different for the two loops. This data is typical: Warm-up, 7:30 pace; heart rate 142. Cool down, 7:30 pace; heart rate 159. Gosh, track workouts must be really tough on the body!

A side benefit of graphing my heart rate is that I am less annoyed when I find myself running faster or slower than I intended. Fast people show up to the fun run? No problem, that's a new data point at 6:30 pace! End up running with the slow group? No problem; that's a new data point over 8:00 pace!

I think that a graph like this is a great way of measuring someone's fitness. My friend, who was also trying to keep her heart rate reasonable on recovery runs, wanted to know if we'd be able to run together, and a quick look at my graph told her that we would. If you want to know whether you and I can run together, you can easily tell from the graph that I do most of my runs between 7:30-7:45 pace (from the swarm of data points there), and a glance at the scale on the vertical axis tells you that this is usually a conversational pace for me (under 145 BPM).

The numbers on each data point tell you the run's distance, but there's no way to express change over time on the graph, so I made sure to keep track of the data points separately, with the date, in case I want to look at that later. I think that I am getting in better shape, because when I add data points, they are usually towards the bottom, with a lower heart rate for a given speed.

If I really try to peak for some of these upcoming races, and stop doing hard workouts but keep collecting heart rate data, I hope to see the type of thing that started this whole experiment: easy recovery effort, fast pace for the effort level, low heart rate. In other words, I hope to continue to make excellent happen.


Anonymous said...

Is your running pace in minutes per mile or in minutes per kilometer? Thanks.

Alan said...

Minutes per mile.

Daniel Hocking said...

I do the exact same thing. You could probably create a mean line. Then after a run you can see if your point for that day deviated by more than some set percentage. If it falls outside some confidence envelope it could be due to conditions or the course. If you can't explain it with those types of external variables, it may indicate over training (fatigue), dehydration, or mental stress. It could also indicate improvements in fitness or adequate recovery if below the confidence envelope. Something to think about. It might be likely that fitness changes too quickly to get a standard line with tight confidence intervals.