JJM335, when I first read your reply, I assumed that you were disagreeing with my post. But I re-read it, and I see that mostly we disagree on whether fat or glucose is used as a primary fuel in aerobic exercise.
and..
Quote:
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Slow twitch muscle fibres are rich in mitochondria and are therefore adapted for metabolism through the TCA cycle. They are rich in myoglobin an oxygen carrying protein. In contrast slow twitch fibres have few mitochondria and little myoglobin. They are primarily adapted for anaerobic metabolism of glucose via the Emden Meyerehof pathway.
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I assume you meant fast twitch for the few mitochondria group - <phew> I thought for a minute I had muddled my fast and slow twitches up
I checked up and you may be interested in this...
and basically we are both wrong, and the picture about what fuel muscles will depend upon becomes much more complicated.
In the fasting state - low insulin levels mean that muscles will primarily use fat as fuel. In the non-fasting state with high insulin levels- i.e. a snack before exercise, and muscles will prefer glucose.
something interesting happens to athletes, in particular endurance athletes. Their muscles become much much better at oxidising fat. Which explains how they can make their glycogen supplies last so long. Also their muscle cells contain very high levels of triglycerides - despite their leanness.
so the actual balance of fat versus glucose, depends on when you last ate and how fit you are.
the article goes on to discuss how people with type 2 and insulin resistance in contrast have metabolically inflexible. They don't switch as strongly from fat to glucose in the non-fasting state, and they continue to utilise glucose in the fasting state.
in answer to your question Wolf, JJM335 is right, any exercise improves insulin resistance. Exercise that leaves you feeling like you've had a workout is the best kind.
The actual cause is down to an enzyme called AMP activated kinase. It is switched on by AMP i.e. the cell being in a low energy state. In muscle cells AMPK switches the genes on that produce GLUT4 (GLUT4 transport glucose into the cell), and so the cell becomes more sensitive to insulin. Depending on the intensity of the exercise the effects of AMPK can last up to a couple of days.
