When it comes to reducing your insulin levels, the benefit of exercise is not that it burns off calories–you have to run two miles to expend the calories you get in one slice of bread– but rather that it gets your muscles to start responding to insulin. Here’s how it works.
Muscles burn glucose and fat for energy. They also store some fuel to have available for immediate use. If you work your muscles long enough–approximately 20 to 25 minutes–they tap into their glucose stores. To replenish those stores they start responding to insulin. Insulin can then open gates on cell walls and let glucose in. The object of exercise is to make this happen, to deplete the glucose stores in your muscles so they go from being insulin “resistant” to insulin “sensitive.”
What kind of exercise will do this? By far the biggest consumers of glucose are your walking/running muscles. They make up approximately 70 percent of your muscle mass. These are the muscles you need activate to restore your sensitivity to insulin.
How Far?
Your muscles’ responsiveness to insulin is an “all-or-none” phenomenon. Like a switch, it’s either on or off. When you start to exercise nothing happens until your muscles do enough work to begin tapping into their glucose stores. Then the switch flips, and they start responding to insulin.
How far do you have to walk or run to get your muscles to do this? About a mile and a half or approximately 25 minutes. Does it do any good to walk farther? Maybe a little, but research studies repeatedly show that you get most of the metabolic benefit in the first mile and a half.
Although it’s popular these days to use a fitness watch to add up the number of steps you take in a day, you can’t get your muscles to respond to insulin by breaking that mile and a half into smaller increments. It must be done all at once.
How Fast?
Because your walking muscles are powered by slow-twitch muscle fibers, they can work for hours without tiring out. That’s because slow-twitch muscles are full of tiny energy producing dynamos called mitochondria that can restore the energy your muscles use as they are working. They don’t accumulate an energy “debt,” which is what causes muscles to fatigue.
It turns out that your slow-twitch muscle fibers are the ones you need to exercise to restore your body’s responsiveness to insulin. In other words, the kind of exercise you need to eliminate insulin resistance is exactly the kind that cause the least amount of fatigue. As long you don’t walk so fast that you exceed your slow-twitch muscles capacity to restore their energy as they are working, your legs won’t get tired and you won’t get short of breath.
Here’s how fast you need to go. When you’re walking, not for exercise or relaxation but to get someplace on time, you give yourself enough time to avoid having to run, but you don’t dawdle either. You work your slow-twitch muscle fibers hard enough to get to your destination on time but not so hard they tire out. That’s how fast you need to walk to restore your muscles’ sensitivity to insulin.
How Often
Here is where most people’s exercise program falls short. They don’t do it often enough. The effect of exercise on your muscles’ responsiveness to insulin lasts from 24 to 48 hours. It doesn’t matter whether you walk a mile and a half or run a marathon; in 48 hours your muscles lose responsiveness to insulin. That means to keep your muscles responding to insulin you need to walk or run every 24 to 48 hours. This why the Surgeon General recommends that you walk 30 minutes 5 days a week.
Bottom line. You don’t have to exhaust yourself. You just need to do as the Surgeon General says: walk 30 minutes continuously at a normal pace 5 days a week. That’s all it takes to keep your muscles sensitive to insulin and eliminate the hyperinsulinemia that pushes fuel into fat and wears out your insulin making cells.
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