This week my schedule got mixed up a bit. Normally I run intervals on Tuesday, tempo on Friday, and my long run on Sunday. However, this week my long run shifted to Saturday (the Marine Corps Marathon on Sunday basically shuts down my regular long run routes). As for my normal weekday track workouts, the two were combined into a single workout on Wednesday morning - the "25x400."
The workout is (as you would expect) twenty-five repeats of 400 meters each. Normally, when I do 400m intervals, I run them at mile race pace (~85 seconds) with a very slow jog for 200 meters after each to catch my breath. But for this workout, the goal was to run each repeat at 10K race pace (around 95 seconds for me), with short recoveries of 100 meters after each. Furthermore, each recovery was to be run in 30-35 seconds (8:00-9:20 pace), substantially faster than the shuffle-jog I normally use to recover.
The workout has two purposes - one is as a lactate threshold ("LT") workout. By alternating paces above and below your lactate threshold, you are able to average LT effort for a longer time than you would during a continuous workout.
The other purpose is mental callousing. It takes a lot of focus to run 25 repeats on the track, especially when you can't check out mentally during the recovery, both because the recovery is so short and because you can't slow down too much during the recovery.
You never get to use the brakes during this workout - you just alternate how much pressure you have on the gas. And while recoveries are a key aspect of any workout, they were integral here - requiring as much concentration and work as the interval itself.
And there's also the fact that, at the end of the workout, you've run 31 continuous laps on the track - a bit less than 8 miles. This is because, after completing each 400, you run the 100 to the next corner of the track, so that each repeat starts and finishes at a new point on the track. As my coach put it, the workout is a head game.
It's also a good simulation of the marathon in many ways. A good friend who had done this workout several years ago advised me to start it conservatively and feel my way in - it's a long way to run, and if things go bad halfway through, you'll be suffering for a long time. Just like a marathon.
And at multiple points during the workouts (starting about seven reps in, if you're me), you realize just how far you still have to go. Just like a marathon.
But the beauty of the workout is that it also sets you up for success. You just focus on running the current interval, and since each interval is just one lap of the track at 10K effort (or 100 meters at 8:xx pace), each interval is easily manageable and not that imposing on its own. So you work your way through, taking one rep at a time and then you're at the last lap and it feels awesome.
As for how it went? Fairly well, I think. I heeded my wise friend's advice and made sure not to start too fast - this was pretty hard to do, since the pace feels so stupid easy during the beginning (again, just like a marathon). I tend to be a rhythm runner, so once I got my feel for the pace of the interval and the recovery, it wasn't too hard to shift back and forth. Not every interval was exactly 95 seconds, but they were pretty darn close, and I had enough left to "kick" into sub 6:00 pace for the 25th and final rep.
There was one hiccup: I realized early on (after the first rep) that I didn't know where the other 100m lines were on the track. I was only familiar with the mark my team uses to start/finish our workouts, not the other three. And in the darkness of the early morning, it was really difficult to see where the track was marked. So I ended up working off of other things in the area where the 100m line should be - generally painted markings on the infield bordering the track. Doing this way probably means that some of my recoveries were a few feet longer than 100m, while others were a few feet shorter. I don't think this really mattered - what was important was that each 400m lap stopped at the same point it started and that the recoveries averaged out to 100m.
I did have one question about this workout. It's done by runners with a range of abilities - on the one hand there are those who run 10ks in roughly 32 minutes, and so run their repeats in around 75 seconds. On the other end, you have myself. I run a 10K in about 40 minutes, and my repeats in 95 seconds. So why do all runners get the same recovery of 100m in 30-35 seconds - a pace that is relatively much quicker for me than for them?
After thinking about it, I realized that it was because this is a lactate threshold workout, and we are trying to average LT effort. Lactate threshold is generally defined as the pace one can hold during an hour-long race. So...if you race 10K in 32 minutes, your 10K pace is a lot faster than your LT pace - there's a wide gulf between 32 minutes and 60. On the other hand, since I race a 10K pace in 40 minutes, my 10K pace is closer to my LT pace. In order for both runners to average to LT effort, the 40 minute 10K runner needs to keep the recoveries more active. The 32 minute guys are running their repeats harder, and so get relatively easier recoveries to balance out the effort.
And that's probably also why this is not a workout that will work for runners of all paces. At some point, a runner's 10K pace is too close to the recovery pace, and so the recovery pace is too fast for them. At that point, it makes more sense for that runner just to do the standard continuous tempo. The other option would be to give that runner more time for recovery, but if you do that, then the average effort for that runner won't be lactate threshold. And the runner will also be on the track for a very long time. The workout itself, excluding warm-up and cool-down, had me running continuous circles for ~52 minutes - I don't think it's a good idea for most runners to be running continuous circles for too much longer than that. Crazy ultra runners, as always, excepted.
One more week of hard training, and then I taper.