A couple days ago a reader dropped me note and had an interesting question.
Donald is doing his speed work based on his 5k time. We should point out that the he stated that it was based off a time he has run, not a “wishful thinking time” as Don said. The problem was though, that as the repeat distance increased from 400 meters to 600 meters and above, he could no longer hit the 5k pace. So the question is, what gives?
You know me, there’s never a simple answer, but I’ll try to break down my thoughts on this as short as I can.
The very first point I’d like to make is that this is why I don’t usually prescribe 5k pace training during the marathon. Here’s why, Don stated he’s a pretty new runner. So my guess is that he ran that 5k PR even earlier and probably wasn’t training as much as he is now. I know it seems counterintuitive, but think of this way- when training for that 5k, let’s say he was running 20ish miles per week and probably running a few days per week. Within that week, he was probably doing a speed workout a week and a moderate length long run. Needless to say, he was fairly fresh when he ran that. Now, he’s probably running 40+ miles per week with two workouts and a long run in the week. You may have heard me say that speed is relative and this is exactly what I am talking about. Doing a bunch of work at 5k pace is important for 5k to 10k races, but 5k pace for a marathon isn’t as big of a deal. Doing the speedwork at 10k pace is plenty fast for 95% of the people we work with.
The second part to this has to do with some hard physiology. 5k paced training is designed to be pretty close to VO2max, just slightly under. The time we can run at our VO2max varies based on our ability. A world class 5k runner can run close to 2 miles at their VO2max. A newer runner, probably more like 3 minutes. So given this, it makes sense that Dons workouts would start falling apart as the repeat distance increases. 400’s for Don would be about 1:42. 600’s would be 2:33 and 800’s would be 3:24. Seeing this, it now makes sense that Don’s workouts start falling apart after the 600 distance repeats. He simply has reached the max amount of time that he can sustain that pace. The farther he runs, the worse the workout will be. In this case, he reaches pretty close to VO2max in the first couple repeats, and then he’s literally maxed out so that each following repeat will simply be slower and slower. The longer the repeat, the worst it will be.
So, my recommendation is for marathon training, keep speed at 10k pace OR only do 5k workouts that will keep each repeats under that three minute range for beginners and around 5-6 minutes for more advanced runners. Other than that, please know that you will get what you need from doing the work at 10k pace. The marathon isn’t about working on overall speed, but rather the speed necessary to run your best marathon. To increase your overall speed, I recommend doing a separate training segment where you can work on all paces from 10k down to 5k and even mile race pace!