Detraining: How far can you fall?

Over three years of detraining, my anaerobic and aerobic threshold speeds have declined 23% and 26%, respectively. At a climb rate of 1,000 meters per hour, my heart rate has increased 37%. Detraining, age, altitude—and attitude—are all factors.

An image of my declining Performance Management Chart and a graph of my most recent lacate test
A glimpse of my declining Performance Management Chart and my lactate test in April 2022

Back in February 2019, I did a lactate test and hit a personal record in climb rates1 at my anaerobic and aerobic thresholds. A month later, I succeeded in my goal to not DFL2 at the ISMF World Championships in Switzerland. I finished the season 6th in Canada overall.

But today, I'm in a very different position. Three years is several generations in the short life of mitochondria. I'm near-sedentary, and my fitness has fallen off a cliff.

How far has my fitness fallen? On a recent trip home to Canmore, Alberta, I fired up my NordicTrack incline trainer, calibrated the crappy accuracy out of it, and did a lactate test.

A graph of changes in Chronic Training Load (CTL) over three years of detraining
My Performance Management Chart, showing the effect on Chronic Training Load (CTL) of three years of detraining.-



I haven't trained in three years. My motivation for training peaked in 2019 (and then slooooowly troughed). Since then, I've made a few half-hearted attempts at getting back on the horse. But living in a non-mountainous environment, the COVID-19 hassle with training (venues) and racing (masks), and my changing priorities conspired against my fitness. Instead, as my Training Peaks CTL chart shows, I'm barely non-sedentary, and only doing the random and occasional run or bike ride.

My Chronic Training Load (CTL)3 has plummeted. My CTL has dropped 95% (from 124 to 6) between January 2019 and April 2022. That coincides with a drop in training volume from 730 hours in my final skimo season to 166 hours in the 365 days previous to my April 2022 lactate test.


I now live at a much lower altitude. For the past 2.5 years, I've been sleeping at 1,000 above sea level (ASL) and living at 500' ASL (work, school, and life happen slightly lower than where we live). When I was training for skimo, I lived at 4,300' ASL and trained at or above that same altitude.

I don't live in the mountains. This is a motivation issue more than anything. I now live in the green hills of Vermont and miss the jagged limestone of the Canadian Rockies. (The skimo scene is incredibly keen here, so my low motivation is all on me, not Vermont.)

My sons are growing up, and I don't want to miss it. Our oldest son is 18 and just got his own apartment. Our youngest son is 12, soon to be a teenager. I can feel that the natural progression from boys to men is only going to increase and accelerate. I'm greedy to maximize my time with them rather than with my heart rate monitor.

Testing Environment

Both tests were done on a calibrated NordicTrack incline trainer at a 25% grade and at 4,300' ASL. Most treadmills, NordicTrack included, have really shitty speed accuracy. My treadmill typically reads 16 to 19% slower than the actual speed. A friend's (same model) reads ~12% slower. (Unless it's a Woodway, you need to calibrate your treadmill to get accurate results.)

My PR test was on February 19th, 2019. That was one month before competing at the World Championships and during my best season ever. I finished 6th overall in Canada, and my best race result was 3rd in the sprint at Canadian Nationals. At the time, I was 45 years old, 69 kg, and fairly lean.

My detraining test was on April 4th, 2022. I tested at the same altitude as all prior tests but after only 48 hours of acclimatization. The elevation is not extreme, but fully acclimatizing from 1,000' to 4,300' would have removed the altitude as a variable. I didn't have time to properly acclimatize, and I suspect that that affected the results. (I hope to do another test when I'm home again for the summer.) Today, I'm 48 years, still 69 kg, but I'm sure my body composition has worsened.4

A graph comparing two lactate tests, one at peak and the other, detrained
A comparison of two lactate tests: My PR test from February 2019 and my current (detrained) test from April 2022.

Test Results

My anaerobic threshold speed has dropped 23%. At ~4 mM5 my anaerobic threshold (AnT) pace has fallen from 1,530 meters per hour to 1,180. My anaerobic threshold heart rate increased 4.3% (from 188 to 196).6

My aerobic threshold speed has dropped 26%. At ~2 mM7 my aerobic threshold (AeT) pace has fallen from 1,360 meters per hour to 1,000.8 My aerobic threshold heart rate increased 7.4% (from 176 to 189).9

At 1,000 meters per hour, my heart rate has increased 37%, from ~138 to 189. My maximum heart rate in 2019 was 210, and my recent lactate test suggests—with a ~4 mM HR of 196— that I still have a similar maximum. So assuming that my max HR is still the same, that's an increase from 66% of maximum to 90%... Not good: 1,000 meters per hour has changed from a recovery intensity to aerobic threshold.

Follow-Up Questions

With proper training, is my previous peak "restorable"?

Probably not. My capacity is probably age-diminished. But more importantly, my motivation for that level of structured training is low. (Been there done that, I want to hang out with my sons, and buying an engine looks like it'd be more fun than rebuilding one.)

If it were restorable, would it come back quicker?

Probably. Age factors aside, it's faster to restore fitness than it is to create it. So even if my potential peak is permanently lower, I suspect I could reach it faster than the first time around. Also, there are some training strategies that I had planned for 2020 that I never used. I suspect that they would be beneficial if I added them to my program.10

But motivation is key.

And at the moment, I don't have it. I'd like to do some grande course events in Europe, but my performance expectations have fallen with my skimo priorities. My main motivation to do them is because they'd be fun, a good challenge with good friends, and a great method to slow more age-related decline.


Homeostasis is vicious.

What you don't use, you lose. When he was 54, I asked the uber-prolific Steve Swenson how he stayed in such good shape:

I never stop. If I do, it takes too much effort to get back to where I was.

Now I really understand what he meant. And today, "The Colonel" is 68 and still going strong.

My fitness has fallen off a cliff...

As age-related decline continues, staying active will become more and more important. I want to keep up with my kids as long as possible. And, I'm reassured, with the general dearth of effective training advice in most sports, I should be able to do so for quite some time unless they become serious endurance athletes.

...but not as far as I thought.

My threshold paces of 1,177 and 1,000 meters per hour are still decent. And I could temporarily notch them up just by being regularly active and throwing in a tiny bit of strength and intensity.

Or should I just buy a Porsche?

  1. Note that all of these climb rates are very context-specific: wearing running shoes on a treadmill at a constant incline. Due to heavier equipment and variable terrain, climb rates outside are not comparable (and would be lower).

  2. "DFL" means "Dead Fucking Last".

  3. CTL is imperfect, but it's like democracy. It isn't an ideal option; it's just the best one we have.

  4. With a steeply declining training volume and being in my late 40s, I'm sure that I've lost muscle mass. If I've lost muscle mass and my weight has been maintained, that means that I've swapped muscle for fat.

  5. Yes, yes, I know, I know. Four millimoles is not necessarily the anaerobic threshold. But it's close enough. Pinpointing AnT in a lab is not worth the time, expense, and short shelf-life of the result. And comparing changes to a fixed lactate value on a treadmill is much more reliable than an effort-driven field test.

  6. Once a decent base is established, changes in pace are always much more significant than changes in heart rate.

  7. Yes, yes, I know, I know. It's the same as AnT: Comparing changes to a fixed lactate value on a treadmill is much more reliable than an effort-driven field test.

  8. During lactate tests, I've always had a "bench" between 2.1 and 2.3 millimoles. I suspect that this is related to being very fast-twitch. (My lactate after sprint workouts was regularly in the 20s, PRing at 23.)

  9. The change in my aerobic threshold heart rates is probably overstated. Most AeT tests that I've ever done pegged my Aet HR in the low-180s. (It was "183" more times than I can count.) I suspect my lower HRs in my February 2019 test are because of being slightly overtrained. (I felt fine at the time, but HRs were lower than usual.)

  10. In particular, my peak anaerobic and aerobic threshold paces at my peak had a gap of 12.5%: 1,530 / 1,360 = 1.125. With a period of focused "bounce" intervals, I wonder if that could narrowed, if not at the same speed, at least ot a narrow gap, raising aerobic threshold pace to be closer to anaerobic.