How to discover your aerobic threshold
Alan Partridge famously warned, “Stop getting Bond wrong!” I haven’t done that, but I have been getting zone 2 wrong. That’s because I didn’t know where it was.
Last week I posted this as a brain dump of things I’d been thinking and talking about recently.
It’s based around the five zones commonly found in the likes of Garmin, Strava etc and which are based around heart rates and percentages of your supposed maximum.
But all that heart rate stuff is really just a proxy for what’s actually happening elsewhere in your body.
The practical conclusion of this was that I tested myself for my actual aerobic threshold and have started doing runs and bike rides based around it. I’ll stick to it and see what – if any – difference it makes over a couple of months.
Why though?
Zone 2 training should be about 80% of your weekly exercise.
That’s because it trains your body to work efficiently at aerobic levels of intensity. It creates mitochondria – the body’s little energy processors (pictured below) – and builds capillaries around the muscles.
The theory is that if you train your body to adapt this way you build big endurance, gradually see more efficient use of oxygen, get faster, get tired less sooner etc.
And the slow-twitch muscles it trains work better when you work at high intensities because they can process lactate better.
How to not get aerobic threshold, wrong
My light bulb moment about how to gauge aerobic threshold came watching Dr Inigo Millan – sports metabolism expert and trainer to pro cyclists. He said he often does phone meetings while doing ‘zone 2’ training.
His explanation of where to find the aerobic threshold made perfect sense, namely where those on his call know he’s exercising but he can still speak in full sentences.
So, I went out for a run and did that (minus the actual meeting) and found my aerobic threshold to be about 10bpm below my Garmin zone 2.
It got me thinking about how really there are only three zones and what they represent.
- Low intensity, where slow-twitch muscles run on fat stored in the muscles.
- Medium to high levels of intensity where fast-twitch muscles kick in and fat as a fuel begins to be supplemented by the carbs they need. That also means oxygen is needed, CO2 has to be expelled and increasing amounts of lactate are produced. As you go harder things edge towards levels of lactate that your body can’t process for long.
- A very high level of intensity that you can’t sustain for very long at all.
That also means that between 1 & 2 and 2 & 3 there are two thresholds.
- The aerobic threshold, where your use of fat and carbs as a fuel source tips towards the latter. Here’s where your breathing gets heavier as more oxygen in / CO2 out etc is required.
- The lactate threshold, where your ability to process lactate falls below 45 minutes or so. I guess that’s arbitrary but it coincides roughly with a 10k run time.
What I plan to do
Lately I run 2x per week, in between 3x bike rides, all on weekdays with the weekends off.
I’ll keep those runs at or below aerobic threshold over the same route for at least 4 weeks and see if I get any quicker.
I’ll keep most bike rides down at that HR as much as I can, at least for the first part of rides.
I’ll train at lactate threshold levels or above on other days or at the end of aerobic threshold runs/rides.
At some point also I’ll test for lactate threshold so I know where both my boundaries are.
Although this is titled to target VO2max, it concisely sets out a good balance of training
S2Stats 