Aerobic Threshold - the most critical metabolic stat you should know

Updated: Dec 6, 2019

Do you run by heart rate? If you don't, and you want to see significant performance improvements, you should consider it. If you do, are you getting the most from heart rate training? If you don't currently have an understanding of what your body's metabolic response to exercise is, then you're probably not. You're leaving too much to chance to; get the most out of each run, develop the right training plan, and provide the opportunity to develop your aerobic base to its fullest potential.

Running according to heart rate, within the correct data, allows you to monitor your intensity accurately. There's a fine line between over doing it during each run, and getting it just right for each stage of your training. And this take us straight to the heart of this post - why your Aerobic Threshold (AeT) is such a critical piece of data to know.

Why is the AeT so important?

A highly developed aerobic base is the starting point for athletic performance, the cornerstone of endurance (and that's any exercise that lasts more than just 2 minutes!), the path towards losing weight from fat stores, to feeling more energetic, craving less sugar and avoiding injury and over-training.

Knowing your AeT therefore, allows you to train at the right intensity to develop your aerobic base (burning fat for fuel) and not reaching into your anaerobic system (burning sugar for fuel). A common training mistake in many runners and those overly-reliant on too much HITT methods.

I reference Phil Maffetone again below, he's a well-respected coach to many successful professional and Olympic athletes, and he explains all about the aerobic base much more coherently than I can in his post. If you've got an extra 10mins it's well worth the read.

If you're a data geek and serious about taking your performance to the next level, you'll want accurate data around your AeT (and as much of it as possible). Data you can reliably create the best training plan from, to make every run count and maximise performance. And data that you can record regularly, and cost effectively, to track your improvements and progress your training plan accordingly.

Below I explore 3 ways you can go about getting this data.

3 ways you can determine your Aerobic Threshold

Benchmark data

The '180 Formula' devised in the 1980s by Phil Maffetone, is a simple formula based on statistical observations he took from a number of athletes he studied. Its beauty lies in it's simplicity, making it a useful starting point for most people to focus and improve their training. It does tend to underestimate a lower AeT though, which is not a bad thing as most runners tend to over-exert themselves. So this method will help those runners to train more effectively and avoid over-training and associated injuries.

However its simplicity is also its downfall for those who want confidence in the AeT result. Confidence that they are training optimally. Being a statistically based formula, it will be right when applied to the group but not necessarily for the individual.

Maffetone also devised follow up, MAF Test, to measure progress over time. Whilst you can track your improvements, you can't actually determine the specifics of those improvements in terms of bpm. Again, this is useful for most to establish a benchmark and observe improvements from that. However, for others, who will want to modify their training based on measurable progress and adjust their heart rate zones accordingly, the MAF Test falls short.

Metabolic Efficiency Testing

Metabolic Efficiency Testing (MET) as part of a Gas Exchange lab test. During this test you are hooked up to very expensive equipment, wearing a mask, as you pound away on a treadmill. The sensors in the equipment measure the concentration of your expelled CO2 vs your inhaled oxygen; enabling the ratio of fat to carbohydrates, burned as fuel for energy, to be measured. In other words, your metabolic response to exercise. Measuring these ratios over an increasing intensity of exercise, and heart rate bpm, allows not only the AeT but also Anaerobic Threshold (AnT) to be established.

This is probably the most accurate measurement of both AeT and AnT you can establish and provides a lot more useful data aside. However due to the high cost involved (especially if you intend to measure progress), and the difficulty in actually finding somewhere even remotely locally to get it done (and I've tried!), these are pretty much reserved for professional athletes.

These two methods I've described represent both ends of the scale. The MAF test being the easiest and cheapest, and the MET being the most accurate and expensive. There are other more involved 'field' tests you can do, but not explored here. That's possibly the subject of another post. These can be quite subjective to gauge the necessary intensities required for measurement, and difficult to replicate for monitoring progress.

Therefore an ideal middle option is blood lactate testing.

Blood Lactate testing

A graph showing blood lactate levels against aerobic and anaerobic heart rate thresholds

Previously this was really only available to professional athletes, like MET. However portable analysers are now available, making this testing available in the 'field' and not restricted to expensive lab testing. From a small pin-prick sample of blood, the lactate level present at varying intensities of exercise is taken. Plotting these against heart rate bpm enables both the AeT and AnT to be identified (the chart pictured above is a typical example of the type of output from a blood lactate test and shows the results of a well trained endurance athlete).

Not only are the results from this testing more reliable and accurate than the MAF test, they are easy to replicate for monitoring your progress and significantly cheaper than MET. That's why I offer blood lactate testing through our running club as the best way to identify the most critical metabolic stat you should know; your Aerobic Threshold.

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