Basic Exercise Physiology....In My Own Words

It seems lately that I've been explaining to others many of the things I have learned over the last 2 years. First, I read a few books with the intent of being successful with XC mountain bike racing, then I read books with triathlons in mind. After having shoulder surgery, I decided to pour most of my free time into learning to become the best competitive road cyclist that I could be. This, coupled with my fascination for science, has led to somewhat of an obsession with exercise/athletic physiology for me. So, with that said, here's what I have to share:

Aerobic vs. Anaerobic Performance

Most athletes know the terms aerobic and anaerobic. Most of them can probably even tell you that aerobic exercises require the use of oxygen, and anaerobic exercises don't use oxygen. But what does this really mean? It's simple. Most people associate the word oxygen with the act of breathing. Respiration. Moving air in and out of your lungs. For the sake of this discussion, let's say that we're talking about things that happen at the cellular level...that is, metabolic respiration. Moving oxygen in and out of your cells. During metabolism (another word that we've all heard), substances inside our bodies are being "broken down" into things that we can use as energy/fuel. I like the term fuel, as it implies that my body is about to do some work! So, just remember that when we are aerobic, our cells are able to use oxygen to help metabolize substances (mainly glucose) to provide fuel for our muscles to keep contracting (working). When we go anaerobic, the switch is flipped, and we begin using something called phosphocreatine (which is stored in the muscles), instead of oxygen, to make the fuel for our muscles. As far as this discussion goes, that's all you need to know about the terms aerobic and anaerobic.

The Heart Rate Discussion

When you ride your bike, the harder you pedal...the harder you breathe, right? Why? The answer, again, is simple. Your muscles are contracting harder/faster, which uses more fuel. In order to produce that fuel at the rate that you're asking (aerobically speaking, of course), you require more oxygen (remember....breathing at the cellular level). Your lungs take in more air, and the oxygen is filtered out and moves further into your body eventually making it to your cells. (Yes, I know there's more happening, but this is a simple discussion, remember?) Since it takes blood (specifically, hemoglobin) to transport the oxygen to your lungs, your heart beats faster to get it there. This is why heart rate provides a relatively good measure of the amount of work that your body is doing at the cellular level, in order to keep your muscles working.

So...how do I use heart rate to train/race smarter? (I thought you'd never ask!)

1. When our cells are working at a low-aerobic rate...consuming a relatively low amount of oxygen, athletically speaking...the primary fuel source is fat. So, in theory, you could ride until you had no more fat content in or around your muscles...0% body fat! (This isn't true, but for now, let's pretend it is). From an athletic performance standpoint, at this low heart rate, your body needs little more than oxygen and fat to keep going (maybe some fluids...!)

2. If we raise the level of intensity a bit, and perform at say...a high-aerobic rate...we begin to require more oxygen - and a different fuel source. Our bodies are looking to "sugar" for energy. Our muscles store about 90 minutes worth of usable glycogen as fuel. So, again, in theory...if we didn't consume any more sugar during exercise, at this level of intensity we could only perform for an hour and a half.

3. When you perform a massive amount of work on the bike, such as a "quick jump" or sprint, or a bold attack, etc...those are circumstances when you have the ability to truly go anaerobic (finally!). When you do this, you're breathing super heavy, aren't you? At this point, your cells are trying to make fuel faster than your body can supply oxygen for the amount of work that you're doing. To speak technically again for a moment, your body turns to ATP and creatine for fuel. You only have enough to maintain this monstrous performance for about 8-10 seconds!

Sometimes people talk about "Lactate Threshold". Lactate is a waste product that occurs as your cells make fuel. It's removed during normal blood circulation, much the same way that oxygen is delivered to the cells. Eventually, it makes it's way through the kidneys and is eliminated from the body via urine. Lactate Threshold (LT) is the point at which lactate is being produced faster than it can be removed from the muscles. The result is that rubbery, burning sensation during intense exercise (sprinting, attacks, heavy weightlifting, etc), eventually leading to the inability to work any longer. This can also be measured as a level of heart rate. There are numerous field tests that you can do to determine this number. Joe Friel and Chris Carmichael both have fantastic ways of doing this (in my opinion). Both of those authors also provide methodology for determining the proper "heart rate zones" in which to train, in order to achieve certain desired results.

Note: Reaching lactate threshold and eventually developing the inability to work is NOT "bonking". Bonking signifies running out of fuel.

Now that you understand that, you can begin to realize some of the things that are important for endurance athletes to remember. Refueling the fuel tank before it gets empty, staying out of the anaerobic zone as long as possible, lowering your work effort when you have the chance to conserve fuel storage, to name a few.

Since I've been perfectly clear up to this point, let me confuse you a little...

Using heart rate as a training method is hugely beneficial. In response to endurance (aerobic) training, your body makes changes in order to be more efficient in using the extra oxygen. That's the most non-technical way to say it. Those changes don't occur overnight. They take some time. Also, some changes are heart rate specific. For example, mitochondria production and increased capillary beds are aerobic changes, that happen in lower heart zones. In contrast, lactate threshold training obviously cannot be done at low heart rates. I'll refrain from posting the zones and how to obtain them for now.

..........So there you have it. A simple explanation of some basic exercise physiology. Of course, this is just the tip of the iceburg, there is as much information out there, as you're willing to go find. Please, feel free to leave any comments or questions about anything I've said. As always, I appreciate the "wave"!

*Here is the same writing, in PDF form.*