This article was originally posted by Ryan at the original HillRunner.com Blogs.
I like the general point of this article. I’ve long believed in training by time, though I accept that most people will think in terms of miles so I think of a target time, the expected pace of the run, then assign a corresponding distance. Want at least 1 hour and expect to run around 7:00 pace? Go for 9 miles. Want at least 1 hour and expect to run around 9:00 pace? 7 miles will get you there.
One place I think the author makes a mistake is in describing the workout. The 15:30 5K runner and the 18:00 5K runner running a 5K pace workout are not running at the same intensity. The 15:30 runner is running at a higher intensity than the 18:00 runner. What’s more similar to 15:35 (shouldn’t it be 15:30?) at 15:30 race pace, 14:28 at 18:00 race pace or 18:00 at 18:00 race pace? The problem is the author discusses focusing on time and intensity, then ignores the difference in intensity between the 15:30 5K and 18:00 5K. Maybe this doesn’t seem like a big deal but think of the difference between a 15:30 5K and a 20:00 or 25:00 5K. Same concept. As he mentions, the body doesn’t know distance, it knows time and effort. This doesn’t mean the workout shouldn’t be adjusted but the reason given is, in my opinion, questionable. Maybe you need to increase recovery duration so your ratio between work and recovery remains similar. Maybe you need to shorten the workout for other reasons, such as the possibility that the 18:00 runner may not have the same base and work capacity as the 15:30 runner (though the inverse could potentially be true of course).
In the end, I’m not trying to be critical of the author or what he wrote in general. I fully agree that the body knows effort and duration. It doesn’t really know whether you’re running 9 miles or 10. It knows you’re running 70 minutes at some given intensity. That said, we should carry this premise through to workouts and realize that a 15:30 5K runner and an 18:00 5K runner are not running the same intensity at race pace so targeting the same time means the 18:00 5K runner has an easier workout than the 15:30 runner. Maybe that’s called for given other factors. Maybe, though, it isn’t.