Threshold consistency - how consistent is consistent enough?

Question

I'm running 5 minute repeats on a track, with a rest after each one of a minute, and I've been told to run them consistently, rather than going out fast on the first one and then getting increasingly slow over time.

If I'm aiming for 1:38 per lap of the track, what counts as 'consistent'? I suppose ideally you'd do every single lap at exactly 1:38, but that seems impossible (if nothing else, from inconsistent timing).

So how close should each lap be to the ideal lap time? Is within 1 second good enough, or should I be more stringent?

Here's a graph of the last two times I did this; the first time is less consistent than the second (well, I did get consistently slower quicker the first time I attempted this) but I'm not sure where I should be aiming to tighten things up - when does it appear I stopped being consistent enough on the second attempt?

Answer 1

Based on your times, I'd recommend moving your goal to 1:40 per lap, and then go no faster than 1:38 on any lap. The idea of shooting for a specific time works because as you get tired, you still have that goal in mind, and can work harder to reach it for each interval. You start out well under your goal on July 30th, but even by the 3rd interval you're missing your splits. This type of pattern can lead to an acceptance of slower times on later repetitions, which makes it difficult to push yourself and get faster. By keeping your splits all at a constant pace, you'll have a better idea of how hard you need to go on the later intervals, and can adjust accordingly, rather than simply going at a pace which feels doable.

You should also try to bring down your times more on the last 1-2 intervals, when the workout is close to being over. Shoot for a 5th interval at least as fast as any previous interval, and then shoot to beat that time on the 6th. These are the pieces you should be pushing on, not the 1st and 2nd ones. The last lap especially should be significantly faster; practicing this speed increase at the end will help to give you confidence in your overall endurance.

Answer 2

You should be aiming to hold a specific pace. It's not "impossible" to hold within a second or two for every lap, just about any decent college runner can run 4 laps and tell you his time (without a watch) within a couple seconds for each one. This is just pacing experience.

For the intervals you describe, you want the entire effort to be as consistent as possible, the entire time. If you can easily make the pace at the first one as well as the last, then your target is a bit too easy. If you can't make any, it's a bit too hard. It will take time to get this pacing correct, but once you do you can easily adjust subsequent workouts.

Eric refers to training with power, one of the seminal books on bike training (Training and Racing with a Powermeter) suggests that if you are doing intervals and your pace/power begins to drop, that you stop the intervals. Trying to complete the intervals at a lower level defeats the purpose of the workout, and that you are better served by redoing the workout at a later date at a more appropriate pace. Conversely, if you make all the intervals at the goal pace, then you should add intervals until you can't hold the pace and then the next time, adjust from the beginning.

Answer 3

You are doing intervals to put an intense load on your system. It's important to keep that load relatively constant to get the best benefit from them. You can also use this to tell if you need to stop early; when an interval gets lots slower than the previous one, you are done for the set (and perhaps for the day if you're doing multiple sets).

I don't do running intervals, but when I do intervals on my bike, I see a 5% variance in power often. I wouldn't worry too much about small variances.