Losing fitness in zone 2?

Hi,

There are a number of things to consider if you want a meaningful comparison between runs:

Are you using a chest strap for accurate recording of HR?
Are you running the same route with the same changes in elevation?
Are you running the same time of day and similarly hydrated and fed?
Is the temperature the same for each run?
Is the wind the same for each run?
Is your day to day stress the same?

Each of these will affect HR and some will affect pace. As you can see, comparing the two as you are, isn’t the right way to benchmark progress or lack of it. Try to benchmark once a month or every couple of months, when all of the above are comparable.

For comparison, I’ve attached an image of my average HR and pace for all runs over the last 10 months.

I’m definitely fitter now than I was in January and at a race at the end of August, knocked three minutes off the previous year’s time. My average HR (which matched my AnT) and max HR for the race was exactly the same as last year but I was quicker. However, my day to day pace and HR are not comparable for all the reasons above.

OP, yeah, I’ve noticed pretty much the same thing and don’t have a good explanation for it. I was keeping pretty good track of the usual environmental variables and not really getting faster at the same HR–if anything, I was getting slower and RPEs were dropping, it felt like I was having to shuffle to stay on Z2 whereas at the beginning of the cycle I was running at a not-hard-but-not-easy pace, and of course I was going measurably slower as well. My first hr drift test yielded an AeT HR of 150 bpm at right under 10:00/mile and I was doing training runs at like 145 bpm and 11:30-12:00 mile.

However, I tried an HR drift test targeting pace (9:15ish/mi), RPE (see above) and breathing (deep but slow and nasal) and actually saw negative drift at an average HR of 165, getting faster at the same HR over an hour effort. My pace:hr did not improve, but my sustainable pace did (for the same formalization of sustainability.). I also had pretty robust AnT numbers at the time, and I was confident that I hadn’t accidentally found my AnT (I mean, breathing, RPE, etc. all pointed in the direction of a valid AeT result, but it’s nice to have the AnT results to validate that as well.). I spent the rest of the cycle training off 165 bpm as AeT HR, and all in all it was reasonably succesful.

I don’t think I’ve heard of this happening to anyone else, and I don’t really have any serious theories for why it could have happened (too much weightlifting in my formative years –> little or no eccentric left ventricular hypertrophy?? the answer will shock you!), but it seems pertinent enough to be worth mentioning. Scott Johnston told me that pace and rpe dropping at a given HR is a sign of undertraining–I don’t believe this was my problem, but maybe if running is only a small part of a guy’s aerobic training volume he could undertrain running specifically while still doing quite a lot. But I don’t know if that even applies to you. Conversely, pace dropping and RPE increasing at a given HR is probably a sign of overtraining, but you’re better equipped than I am to evaluate whether that’s a reasonable possibility for you.

That’s an interesting point. I was probably getting at least half of my weekly aerobic training volume (weekly long effort, 1-2 shorter midweek sessions) from hill laps on trails during the training cycle I described. Something something running economy/fitness/fatigue….