In my last post I explained three things that you must do to be more “fit”, where I define being “fit” as being able to do more physical activities with less effort.
- • make oxygen more chemically available to muscle cells
- • deliver energy to muscle cells at a rate that maximizes oxygen consumption
- • increase the strength of individual of muscle fibers
You can read that post and the rationale behind these fitness imperatives here:
The only exercise modality that accomplishes those three things is High Intensity Interval Training (HIIT). Let me take them one by one.
The Bohr Effect – As I explained previously, almost everyone delivers MORE oxygen to their muscles than the muscles can actually use, even when breathing normally.
The problem is that the hemoglobin that transports the oxygen is chemically “sticky” to oxygen molecules. That makes it a great transporter, not such a great deliverer. (Is that a word?)
Think of it like a mailman who does a great job of bringing the mail to your door but then demands you be there to sign in person before he’ll hand it over.
However there is a metabolic adaptation called the Bohr Effect that reduces hemoglobin affinity for oxygen. When your blood becomes more acidic or CO2 levels rise hemoglobin releases oxygen more easily.
It’s a trade-off. The hemoglobin now transports less efficiently but delivers more reliably. Think of it as getting a new mailman. This one carries less mail in his bag but he’ll drop the mail in the mail slot without a signature. Given that most of us are transporting to muscles more oxygen than needed, this metabolic adaptation results in greater fitness for most people.
There are two things you can do cause the Bohr Effect to kick in. The first is training at high altitude. The higher ratio of CO2 to oxygen at higher altitudes causes your hemoglobin to release the oxygen it absorbs more easily. This is why many athletes train at high altitude before a big event. The effect takes some time to wear off (2 -3 days typically) so when that athlete changes to a lower altitude they get the double whammy of higher oxygen ratio combined with greater oxygen availability to the muscle fibers. Consequently they perform better.
The second thing you can do is raise the acid level immediately surrounding your muscle fibers.
Remember from the last post we talked about pyruvate? Pyruvate is the compound that delivers food to your muscle cell mitochondria for conversion to energy. But the rate at which pyruvate can enter muscle cell mitochondria is limited. When we exercise intensely, an excess of pyruvate builds up and the excess is converted to lactic acid. This excess of lactic acid makes the blood and tissues immediately surrounding muscle fibers more acidic. When blood passes through muscles this greater acidity triggers a local incidence of the Bohr Effect and hemoglobin temporarily releases oxygen more readily.
Wow, that was a lot of big words in one sentence. Let’s go back to our analogy. When you exercise intensely and build up lactic acid it is as though you have a mailman (hemoglobin) who can carry lots of mail (oxygen). Normally he requires a signature. But when he gets to your house a barking dog (lactic acid) harasses him and he drops the mail in your drop box and runs.
OK, I’ve probably extended that analogy as far as it can go (and over-indulged in mailman stereotypes). The bottom line here is intense exercise causes a presence of lactic acid around our muscle fibers and that results in oxygen being more readily available locally to our muscles. More oxygen equals the ability to do more with less effort.
That ran longer than I thought. I’ll break now and next time we’ll talk about how to deliver energy to muscle cells in a way that maximizes consumption this new oxygen that we’re delivering.