Surprisingly low aerobic threshold (drift test)

In my first experience following a structured endurance-focused training plan, my anaerobic threshold (AnT) heart rate increased by 20bpm over a 3-month period. My aerobic threshold (Aet) heart rate at the end of that training block was equal to my AnT heart rate at the beginning. My years of intermittent running & powerlifting did not translate into a high AeT.

It sounds like you’ve been methodical about dialing in your AeT. You could consider getting a second opinion via a lactate test (I believe many people on this forum have gone to the lab at CU Boulder). Or base your training on these results, and spend a few months training below 110bpm, and re-test.

The age-based heart rate ratios apply to populations but with huge individual variance – best to ignore those.

Correct me if I’m wrong, but I thought one of the main goals of an endurance-focused plan is to increase your AeT? That way, the difference between your resting HR and AeT increases which gives you a bigger cushion to do harder activities while remaining in your aerobic zone. For instance, hike/run faster on an approach while staying in the aerobic zone (which is more efficient since you primarily burn fats for energy vs. carbs)

Yes. The first, least-informative adaptation is heart rate. Threshold heart rates (for both AeT and AnT) will rise and converge.

But what really matters is speed. While the HR changes may happen in a matter of months, threshold speeds can improve for years (while heart rates don’t change).

…it sounds like the difference between AnT and max HR is just the amount of time you can sustain it for? Max HR is a few seconds, but for AnT you should be sustaining the “maximal effort” for 30-60 minutes

Not exactly. “Maximum” is always duration-dependent. For example, the maximum speed that you can maintain for five seconds is a lot faster than the maximum speed that you can maintain for 60 minutes.

With threshold tests, you’re not trying to maintain a heart rate. You’re maintaining the highest sustainable speed–or, less perfect, an effort level if speed can’t be measured–that you can for a given duration. Then after the test, you can find out what your average heart rate was. During the test, there’s no need to even look at your watch to find out.

Does that make sense?

Whenever a prescription is “as hard as you can for X minutes”, it does not mean that you should go out at a full sprint and hang on for dear life until the bitter end. In that mistaken case, your average speed will be far lower than what it could have been with a more measured approach. (The For Dear Life method is also affectionately known as the strong-like-bull-smart-like-tractor approach.)

In contrast, maximum heart rate is the fastest rate that your heart can beat regardless of the intensity level. I assume that it is limited by things like genetics, its size, etc. Most importantly, maximum heart rate is not a workout intensity while AeT HR and AnT HR are.

For example, if your AeT HR right now is indicative of lower than average heart rates. in general, then perhaps your maximum is under 160. On the other end of the spectrum are max HRs of over 200. Neither is a measure of fitness, it’s just a way to quantify how fast the pump can pump.

For AnT, the perfect speed would be where you never need to slow down but are still exhausted after the 30 minutes?

Yes, exactly. In reality, you’ll have to ramp up to it to get the best result.

When you say “threshold speeds”, you mean the pace (i.e. mph, steps/min, etc.) that you can produce at your threshold HR?

Yes.

Can those speeds really improve without the threshold HR also increasing?

Ohhhh, yes. With a lot of the right training, the speeds can increase a lot.

It seems like for your body to output more power (higher pace/speed), you need more oxygen supplied to your muscles = higher required HR. Unless your muscles become more efficient at using the fixed amount of oxygen they receive… perhaps that’s the key point I’m missing.

Yes, you answered your own question. This is why training below Zone 2 is so important. You need to increase the mitochondrial mass in your muscles. The more mitochondria, the more fat, oxygen, and lactate you can process.

Taking my AeT as 108 from tests so far…

I usually err on the conservative side and round down to the nearest five. It’s also easier math to calculate other zones and remember them if they have a base of 5.

It also false precision to define a threshold, which is very dynamic, as “161” or “123”. SO I would use 105 as AeT. There’s no downside.

* How should I determine the lower end of zone 1 – another 10% off the AeT?

It’s pretty fudgy, but I usually use 50% of AeT. It’s not really that important though. Anyone who’s training seriously is already motivated to maximize performance, so as soon as the running shoes are on, they’re going to take it right to the line. The upper limit is more important in order to hold us back.

** I get 97 as the top of zone 1 from The Uphill Athlete page for AeT drift test which says subtract 10% from the AeT

Yeah, 10% is the rule of thumb that we use, but in your case I would use 90. ~10 beats is not much of a window. Also, if your new to aerobic training, defining is Z1 is less of an issue. Eventually, with enough multi-year volume, Z2 will become quite fatiguing. That’s when defining Z1 becomes more important.

*** Since we’re talking endurance training, I don’t think I need to be concerned about these

I think it’s worth doing an AnT test though. Because your AeT BPM is lower than average (again, just as a number, not as a performance indicator), it would be good to know how much of a spread you have between AeT HR and AnT HR.

…so would that be small amounts of zone 3 with zone 1 still being the primary percentage of your training time?

It depends on the goal event, but yes, Z3 is the most common intensity at that point.

It’s also worth noting that most people don’t have to worry about that for quite some time. For example, my HR thresholds have been very close for 15 years, largely because of lucky circumstance of a lot of long alpine climbing days from 1999 to 2005. But even after I started structured endurance training in 2014, it took me three years before AeT was too fatiguing for continuous training.

Like you say in the post, it definitely requires a lot of mentally discipline to not train above the AeT in order to build a base!

Yes, but then it can become like meditation. I think of it as “my grocery list pace”. When I’m in Z1 now (which is most of my training), the last thing I think about is intensity. I don’t listen to music or podcasts, so I just zone out, usually thinking about blog posts I want to write.

Nice job consistently adding more time in Z1 / Z2. You might consider deferring muscular endurance workouts until you’ve ramped up your aerobic volume further, and substantially narrowed the gap between aerobic & anaerobic thresholds. If you’re trying to close the gap between a 105bpm AeT and a 160bpm AnT, think about giving your body time to build new, denser capillary networks, strengthen tendons & bones, etc. – structural changes that will take months to start seeing and can continue for years.

I’ve found that 30-45 minute easy aerobic runs four days per week (Tue/Wed/Fri/Sun), 90-120 minute long run (Sat), and some strength / core (Mon/Thur) to be a workable schedule for me. Low volume relative to most of the athletes here. But this has led to pretty good improvements over the past couple of years.