2012-07-17

Diabetes and Exercise Part II: Exercise "Physiology"

Last week, I introduced this series of posts on diabetes and exercise by taking a look at the things you'll need as a diabetic aiming to start an exercise regimen.

To take the next step, you should be aware of some of the things that occur in the human body - diabetic or otherwise - when we exercise. While having some knowledge of the science behind fitness is highly beneficial for everyone, it is particularly valuable for us diabetics. The reason for this pertains to something I mentioned last week:
When it comes to exercise, you will have to start assessing the impact of different kinds of exercise, and different levels of exertion, on your body and blood sugar. As we will see in subsequent posts in this series, the impact of exercise may be immediate, or it may be delayed up to twenty-four hours in the future! As you start out, these impacts seem erratic and unpredictable. So the better-informed you are and the better-aware you are of short- and long-run trends, the better you will be able to control your blood sugar with exercise.
Let's try to take some of the guess-work out of it, shall we?

A Two-Penny Science Lesson
I've read a few physiology books, had all the important biology classes, and applied the principles to my own life through personal experimentation. What I've learned, is that the average person doesn't need to take a deep dive into biochemistry in order to understand what's going on when they exercise. So, I'm about to give you the simplest lesson in exercise physiology you've ever had...

If we ignore the various chemical transformations that occur during human respiration, we can focus on what's really important to the task at hand. To wit, all human energy is made up of the following components:
  1. Sugar
  2. Water
  3. Air
  4. (Insulin)

When you begin to exercise, your body draws on the energy that has been previously converted from sugar, water, and air, and then stored in your cells. The fuel used to create this energy comes from the food you've been eating lately, the water you've been drinking, and whatever oxygen has been culled from your casual breathing. (Insulin is the hormone mechanism that is responsible for delivering the sugar from the bloodstream into the cells.)

This is obviously a limited energy source that can only get you so far. In order to exercise for a prolonged period of time, the body must reach a point where it is converting fuel (sugar, water, and air [and insulin]) into energy on-the-fly and utilizing it to the extent that it can be generated.

This second type of energy is built from the water that happens to be in your body right now, the air that you're breathing right now, and whatever sugar can be had on a moment's notice. Now, everyone has a given quantity of sugar in their bloodstream at all times, so this is the body's "first stop" for aerobic fuel. The next stop is whatever sugar exists in as ready a state as the body can find, starting with the easiest-to-access and progressing steadily toward the most remote sources of sugar. (Insulin is utilized at all stages, because it is required to deliver the sugar into the cells.)

The "stored energy" in this case is anaerobic energy. We use it for short bursts, i.e. lifting weights, sprinting, kicking at the end of the race, and so on. The "directly converted energy" in this case is aerobic energy. The important takeaway here is this: anaerobic energy utilizes energy that is stored readily inside your cells; aerobic energy must be generated and transported into the cells from outside sources first.

Discussion
It is tempting to say that we use aerobic energy for aerobic, i.e. cardiovascular, exercise and anaerobic energy for everything else, but this is not exactly how it works. Technically speaking, everything the body does involves a blend of the two. There is a sequence that is as much logical as it is physical.

The body can't start doing something unless it employs anaerobic energy. Were this not the case, you would have to engage in heavy breathing for several minutes before you did anything simple, like type an email or lift a fork to your mouth to eat. Anaerobic energy, then, is a ready-source of energy that is employed whenever your muscles first act to do something.

Note carefully: A technical feature of anaerobic energy is that it does not require insulin for immediate use. While your body had to utilize insulin in order to store the energy, simply using it once stored requires no insulin at all.

If you have experience lifting weights, you know that the body can often reach a point where further action becomes impossible. You can no longer lift your arms, your legs stop moving, your muscles burn. Even if it doesn't hurt, there is no point to further physical expenditure - it will not occur. This physical barrier is your body running out of anaerobic energy; there is no more left to be had.

If you are engaged in a lighter, more repetitive movement (like running, for example), then your body has an opportunity to generate some aerobic energy before it completely runs out of anaerobic energy. Your heart starts beating rapidly and you start to breath heavily. After some time, the cardiovascular process has generated enough energy to feed the cells during the exericse. Aerobic energy, then, is the energy generated by an individual's ability to create movement from fuel on-the-go.

Note again: As implied from the above, aerobic energy requires a ready source of insulin. Without it, aerobic respiration cannot produce any energy at all. That is why you as a diabetic may have felt your body start to burn and reach a point of exhaustion in a matter of minutes.

Of course, aerobic respiration is not a perfectly efficient process, so eventually this energy source also declines and the body experiences exhaustion. Extending the length of time required to fully exhaust the body is what endurance training is all about. As you engage in endurance training, your body learns to become more efficient at processing aerobic energy. It does this by growing tailor-made muscle tissue that is particularly adept at this, and also by increasing the amount of oxygen that can be stored in the blood at any given moment. (For water, you pretty much just have to stay hydrated.)

In contrast, strength training does not improve the body's efficiency for utilizing anaerobic energy because the process is already highly efficient. Instead, the body grows additional muscle cells so that there is more anaerobic energy "on hand" for the next time you sprint or lift something heavy. In essence, the body builds more storage for immediate energy, but continues consuming it at about the same rate.

Conclusion
Now that you have a general idea of how the body is making use of its energy, you are ready to apply these principles to your own diabetic body. Because diabetics are less-able to engage in the energy conversion process (either from lack of insulin or the incidence of insulin resistence), some extra consideration is required to understand how we can best exercise, what we can expect as we start to undertake a new exercise regimen, etc.

So, in my next article in this series, I will discuss some special considerations for diabetics, including some words on insulin dosing, planning, etc.