Why Black Hole Cardio Is Not A Bad Thing

Black hole training….in simple terms, it’s training that feels difficult, but gets you little in return from either a fitness or health perspective. When we talk about black hole training in terms of cardio this is where most people actually train a majority of time.


It feels hard, which makes them feel like they did something meaningful, but it’s not too hard where they can’t come back the next day or two days later and repeat it. So they fall into this trap of always training at this intensity because it’s the best of both worlds.

In the beginning they might see a lot of progress in their health and fitness, but eventually it levels off because our bodies adapt and need a new stimulus. This leads to people getting frustrated and giving up, or injury and being forced to stop.

This is why understanding the benefits of the various intensities at which to perform cardio is important. It not only allows you to target multiple adaptations in the most efficient way possible, but it also keeps you from plateauing and keeps you from getting injured.

So it’s not that black hole training is bad, it’s that when it’s overdone it becomes ineffective and can lead to the body breaking down (the same is true for high intensity and low intensity training, but like I said above people avoid these intensities because it feels too easy/hard).

In terms of cardio, the black hole training intensity is the heart rate zone between the top of zone 2 and the bottom of zone 5…if you are able to count that would be zones 3 and 4 😁.

If you don’t know your specific heart rate zones, this would be the heart rate range between your MAF heart rate and your max heart rate at an all out effort minus 5-10 beats.

Here is an example for myself based on my VO2 Max test. My zone 2 ends at 133 beats per minute and my zone 5 begins at 155 beats per minute.

There are some physiological benefits of working in between these heart rate ranges.

In the graph above look at what my fat and carb utilization is. Notice I am using more carbs than fats. If you remember back to our discussion about mitochondria and anaerobic and aerobic metabolism, you will recall that as the intensity increases beyond the point we can aerobically generate energy via mitochondria and oxygen we ramp up anaerobic metabolism. The byproduct of anaerobic metabolism is the generation of lactic acid and hydrogen ions. Hydrogen ions cause the burning sensation you start to feel in your muscles and lactic acid can be used by the body along with fat and carbs as another fuel source to produce energy in the body.


Just like we can train the body to become more efficient at using fats and carbs via our training, we can also train the body to be more efficient at utilizing lactic acid and handling the hydrogen ions.

What is the best way to do that?

By training in the “black hole” heart rate range!

In one study [1] researchers had participants do 4 supervised training sessions a week for 45 minutes and 1 unsupervised session a week for an hour on a cycle ergometer. During the supervised training sessions they warmed up for 8 mins at 40% of their VO2 Max (zone 2), then did 20-25 mins at 70% of their VO2 Max (zones 3 and 4), and finally 10-12 minutes of high intensity exercise (zone 5). They followed this protocol for 9 weeks. After 9 weeks participants saw less lactate production at lower heart rates and better lactate clearance at higher heart rates.

Lactate Generation

Lactate Removal


In other words, what researchers observed in this study is that by training in zones 3 and 4, participants produced less lactate in zone 2 and saw greater lactate utilization in zone 5!

However, as we mentioned before, lactate is not the enemy when it comes to exercise performance, it’s a fuel that other parts of the body and organs can use…it’s actually beneficial. Not only does it provide an additional fuel source in addition to fats and carbs for your body, it also appears to be critical in enhancing parts of your health that have nothing to do with physical fitness. One of the many benefits we get from cardio exercise is mental health, and it appears that lactate plays an important role in why that is the case! One of the major consumers of lactate in the body is….YOUR BRAIN!!!! In fact studies have shown that lactate plays an important role in brain health, and may be one of the reasons why exercise is so beneficial for mental health!!! [2]


The real culprit to performance degradation and the cause of the burning sensation in our muscles are the hydrogen ions that build up there from anaerobic metabolism. If we can train our body to remove hydrogen ions more efficiently we can avoid the burn and subsequent degradation in performance. This removal of hydrogen ions is referred to as buffering.

Here is a nice graph from a study[3] looking at the relationship between the ability for muscles in females to buffer hydrogen ions and subsequent decrease in work capacity.


The X-axis is the muscle buffering capacity, the Y-axis is the percentage decrease in work capacity during exercise, in this case on a cycle ergometer.

As you can see, as buffering capacity increases the percentage decrease in work capacity drops…in other words more buffering capacity equates to being able to sustain work output for a longer duration!

So how can we increase buffering capacity? There are a couple of ways, but since we are focusing on cardio in this post, we will keep it to the realm of exercise.

It is no surprise then that exercise can help but as always the question is at what intensity?

In one study[4] done on females, researchers had a control group that did 5 weeks of continuous endurance training below the top of their zone 2 heart rate. A second group of females performed intervals at an intensity above their zone 2 heart rate for 5 weeks. The total work done by both groups was matched. Then researchers looked at which group had the greatest change in muscle buffering capacity. This graph says it all…


The interval training group working above their zone 2 heart rate had a 23% increase in their buffering capacity!!!!!

This is not terribly surprising given you need to challenge your physiology if you want to see changes in that physiological process. The reason why the control group saw no improvement is likely because their exercise was not intense enough to produce a significant amount of hydrogen ions to result in the need to increase buffering capacity. Whereas the interval training group was training above the top of their zone 2 heart rate causing an upregulation in anaerobic metabolism and therefore producing more hydrogen ions. As a result the body upregulates the muscles buffering capacity in order to more efficiently remove them from the muscle.

There is some nuance here in eliciting this buffering adaptation. It’s not just about producing the hydrogen ions it’s also about continuing to exercise despite their production.

For example if you do a 2 minute interval above your zone 2 heart rate and then rest for 4 minutes before beginning your next interval, you may not see an increase in buffering capacity because the long rest period allows the body to clear the hydrogen ions via other means. For this reason you likely need to perform intervals that are longer in duration or shorter intervals with very short rest periods in order to increase buffering capacity.

Clearly training in the “black hole” can have some use. The question then becomes do you need to use it for your goals and if so how do you structure that training and fit it in with the low heart rate and high intensity cardio sessions we know are so beneficial. To find out the answers be sure to check out my next blog post in this series. The best way to know when that will be published is to join my newsletter by entering your email address in the form below and I will email you as soon as it is published!

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  1. (n.d.). | Journal of Applied Physiology – American Journal of Physiology. Retrieved April 27, 2022, from https://journals.physiology.org/doi/abs/10.1152/jappl.1992.72.issue-5
  2. (2021, November 29). Effect of Exercise on Brain Health: The Potential Role of Lactate as a …. Retrieved April 27, 2022, from https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8709217/
  3. (n.d.). Muscle buffer capacity and aerobic fitness are associated with …. Retrieved April 28, 2022, from https://pubmed.ncbi.nlm.nih.gov/15168128/
  4. (n.d.). The effects of training intensity on muscle buffer capacity in females. Retrieved April 27, 2022, from https://pubmed.ncbi.nlm.nih.gov/16283370/

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