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Marathon Sports tip of week: Fuel for thought

Posted by Matt Pepin, BostonGlobe.com Staff  February 17, 2014 03:54 PM

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Quick Biology Lesson: Glycogen is a form of glucose (simple sugar) that is stored in our muscles, liver, and other areas of the body.

What does glycogen have to do with you? Well, thank you for asking. During endurance activities (such as running a marathon) our muscles tap into our glycogen stores in order to maintain energy levels. As our training progresses and runs get longer, it’s important that we pay attention to how we are fueling our bodies.

Most people will typically store between 150 and 300 grams of glycogen in their body (liver, muscles, glands) at any given time. 1 gram of glycogen = 4 calories. That means we have an energy reserve of 600 – 1200 calories. On a long run, most of us are burning
calories at a rate of 600 – 1200 calories per hour. After an hour of steady cardio activity,
we’ve burned through our glycogen – our reserve energy.

One question I frequently hear: “Won’t our bodies start burning fat stores if we deplete our glycogen stores?”

The answer is yes, but because fat is much harder for the body to convert into energy, we need to kick-start that metabolic reaction by burning something else to convert the fat to energy. If our glycogen stores are depleted and we aren’t replenishing them with other sugars, our body will start breaking down protein in order to convert fat stores into energy.

Our muscles are made of protein. We don’t want our muscles to break down. It’s actually more effective and efficient to support fat burning by supplementing it with simple sugars – that way our protein stays in tact.

Think of glycogen as “cash in the pocket” – you know how much you have to spend, and it’s the easiest way to pay for things.

Energy supplements are your “debit card” – almost as easy, but not everyone takes them and you have to be aware of what you have in your account.

Your fat stores are your “mortgage” – it’s real, true money, but much more difficult to convert into funds that would buy you a cheeseburger.

So how much sugar do you need to supplement your energy burn for runs longer than an hour? The rule of thumb is approximately 150 calories per hour – this will adjust up or down depending on your build, level of fitness, gender, etc. One gram of sugar (maltodextrin, fructose, etc) = 4 calories. Most of the energy supplements will be in the 100 calories per serving range. Just in case you’re not good at math, that’s about 1 serving every 40 minutes or so.

Biology and math. All in one tip.

Dan Soleau is Brand Development Manager at Marathon Sports. He’ll provide weekly training tips for those preparing for the Boston Marathon. Dan has completed 6 marathons and an Ironman. He is a mentor for the One Fund’s Boston Marathon team, coach for the Spaulding Rehabilitation Boston Marathon team, and will be running the 2014 Boston Marathon. Follow him on Twitter at @dansoleau or follow Marathon Sports at @marathon_sports

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Look for updates, news, analysis and commentary from the following.
  • Steve Silva, Boston.com senior producer, two-time Boston Marathon sub-four hour runner.
  • Ty Velde is a 16-time Boston qualifier who's completed 12 consecutive Boston Marathons and 25 marathons overall. Ty is now training for his 13th Boston run and will provide training tips for those who train solo and outside, no matter what temperature it is.
  • Rich 'Shifter' Horgan is a 19-time Dana-Farber Marathon Challenge team member who runs in honor of his father, who died of colon cancer. He will provide updates on local running events with a focus on the charitable organizations that provide Boston Marathon entries for their organization's fund raising purposes

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