Interval Duration Question

Interesting. The 2.5% grade on the 400s will have an effect, maybe a significant one. I'd like to see the result after repeating this on the flat or running the 400s in reverse.

Then again, your HR matching Daniel's pictures and spending more time at VO2max with short intervals are contradictory. Particularly when your rest on the 400s is too long. Did you get up to 170bpm much quicker than Daniels illustrates? Again, it could be due to the grade.

With 400m reps I cannot reach my HR higher than 170bpm even at 1500 pace... Max HR around 187 bpm.?

Interesting post and nice experiment. Do you get the same results if you repeat the interval sessions over multiple weeks? Weather, time of day and other factors might be factors. If you're going until exhaustion, why would you hit that point after the same volume of 400s even with shorter intervals and longer rests? That's curious. Were these your first two interval sessions in a long time?

In any case, there are additional advantages to those longer intervals, since you're not just training your cardiovascular system. A better sense of race pace and increased efficiency at that pace are also important.

Thanks for your reply.

Yes, it's a shame I don't have access to flat roads or a track.

Looking at the data though, I think you're right about the hills affecting things. I've plotted the % of each rep over 170bpm and for both it looks like it starts low and increases linearly. For both it starts at 30% and tops at 80%. So, Daniels should be correct. However, if you look really closely, there's a slight bow in each curve: the 1000m curve stays low for a bit longer, meaning I have to wait longer in the session to get high heart rates, and the 400m curve bows the other way, rising faster in the early reps, so I have to work hard earlier. I suspect this is because of the terrain: the 400m intervals are on a gentle gradient which steepens gradually; whereas at the 1000m intervals spot, there's a peak halfway, so just as my HR gets high, I get a bit of relief as I run slightly downhill again.

Sorry, that last reply was to CAA! (still working out this forum).

my 2c: Really I should have averaged data over multiple weeks, but I didn't have the time. I have done a brief check though and it seems consistent between weeks.

No, I do intervals every Friday. I've always tended to rotate around 400, 800 and 1000, but lately I've been trying to do 1000m because of what JD said. My spot for 1000m is a bit busy though, so I'm not that keen.

That's a good point about building efficiency. Mind you, the faster 400m will help form, especially uphill.

It sounds like you guys agree my instinct is right - perhaps alternate between 400m and 1000m each week?

A few thoughts:

The terrain is one issue.

Another issue: was your recovery pace on the 400s faster than with the 1000s? My guess is that it may have been faster as you tried to limit the inefficiency of running an equal distance for recovery (although I guess that doesn’t matter if you were down to the same heart rate at the start of each interval).

As noted, it would be more interesting to see the differences on a more macro scale over time.

Finally, there’s a place for shorter vo2max reps for most people. For me, it’s early or late in a cycle when I either want to get in touch with 5k pace (early on) or lock it in as part of a low stress workout (later on). But we are all a little different, and Daniels intends his guidelines to be a rule of thumb and not a law. What you’ve done, and what others often fail to do, is take the core principle and apply it rather than just being a slave to the guidelines. Good on you. Maybe this trend will continue and you’ll find you’re a bit of an outlier and can benefit from a different style of workout than most of us.

I think for many runners during the first 400m their heart rate would be climbing such that they don’t get to the target rate until maybe 300m as there is some lag. That’s why longer intervals are recommended but I haven’t done your experiment or looked closely enough at HR curves

I’m pretty sure the elevation gain in your 400m reps explains your real world results. I’ve done the exact same experiment as you have done except on a track. The results were as expected and I spent more time with an elevated heart rate at 4 x 1000 m vs 10 x 400m.

Your results are important for you though since that’s where you train and you can use it to your advantage with the knowledge you have gained.

If I understand your post correctly, I come to the conclusion that you are misinterpreting Jack Daniels' definition of his "Intervals", and possibly confusing them with Threshold reps, or you were looking at the 'Threshold' paces in the Jack Daniels Calculator, instead of the 'Interval' paces.

You go on to say this,

...^which just seems to confirm in my mind that you are confusing Daniels' 'Threshold' with Daniels 'Intervals'. If performed correctly, Daniels 'Intervals' should take one's HR above 95% HRmax. They are going to BLAST you.

Here is my HR graph from a recent 12-min Cooper Test, which if run VERY HARD, elicits VO2max (i.e., maximum oxygen uptake), and is run at the Velocity at VO2max (i.e., vVO2max), the minimal pace duration which elicits VO2max:

Notice I first hit what I believe to be my HRmax of 169bpm at 7:43 into the test. (However, I actually registered 170bpm on three occasions later in the test; on one of those occasions, the peak was 172bpm!)

Now here is the HR graph from a recent VO2max 'Interval' session, consisting of 5x1000m/3'Recovery (the 1000m work bouts were ~4min in duration) :

In that session, I tried to hit Daniel's 'Interval' paces, based on the VDOT determined from the 12-min Cooper Test. That session was VERY HARD!

Here are those two graphs using a different image service:

https://ibb.co/NVpjzmf

https://ibb.co/7Y7gTbc