Diabetes Exercise Physiology 200 – Energy Systems

There are only a few more posts from the notes of what I learned from TeamWILD. Today, we’ll go into the aerobic and anaerobic energy systems in a little more detail. I hope to do a whole post on the biochemistry of energy some day, but I need to brush up on my biochemistry first.

Aerobic vs. Anaerobic
[Remember: Aerobic activities use oxygen when releasing energy. Oxygen is plentiful in the environment—Yay!—and helps things burn very well. Remember, the circulatory system moves oxygen to your cells via hemoglobin and removes the byproducts of combustion. Anaerobic exertion does not require oxygen from the blood. It also does not last nearly as long.]

Aerobic exercise involves a combination of carbs and fat. The more intensely you exercise, the higher the percentage of carbs. This is the energy system you’re using from 60 to 80 or 85% of VO2 max. (That is, in zones 1-3 of 5.) The crossover point from aerobic to anaerobic is the “lactate threshold.”

Aerobic exercise is the majority of endurance activity, and it tends to lower blood glucose, both from direct use and increased insulin sensitivity.

Anaerobic activity—zones 4 and 5—is solely carbs. Anaerobic is associated with stress hormones, which may temporarily raise BG.

Because aerobic and anaerobic activities have different impacts on blood sugar and the kind of energy they use, different workouts require different fueling and insulin strategies. [I see this when I go to the gym and lift weights, which often involves bursts of high-intensity, anaerobic work.]

For people with type-1 diabetes, stress can raise or lower BGs, based on how much muscle glycogen there is on hand. Long-term stress causes insulin resistance, infection/illness, and chronic fatigue. Ways to relieve stress: being with friends, exercise, hot baths, mindful breathing, meditation, journaling. [Trying to do all of these at the same time might cause a different kind of stress, though.]

Glycogen
The level of glycogen in the liver has a direct effect on insulin sensitivity. Less background glycogen means more insulin sensitivity.

Higher levels of insulin actually inhibits glycogen metabolism. Normal glucose metabolism means normal glycogen metabolism, so try to get good carb control.

Low blood sugar causes a drain on glycogen stores. So does stress.

  • There is about 500 grams (1 pound) of glycogen stored in the body:
  • 200-400g in muscles
  • 75-100g in the liver
  • 5g in the blood (assuming 100 mg/dL blood sugar)
  • The muscle capacity depends on the level of conditioning. More conditioning means more glycogen capacity.

The body stores 3 grams of water for each gram of glycogen. So a topped up glycogen store implies 2 kg (4.5 lb.) of “extra weight.” But don’t stress: You need it!

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