Timing of caloric replenishment

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Timing of caloric replenishment

Postby rbrnut » Wed Sep 21, 2011 1:34 pm

I've been using the whole regimen of Hammer products very successfully for a few years. After re-reading some of the fueling advice and other articles, I stopped to question something I thought I knew.

I religiously follow the 3-hour rule regarding not eating before a long (90 mins.+) training block and especially a race, being as the research suggests, that muscle glycogen is topped-off and breakfast is to top of liver glycogen levels. So I have dialed in my needed calories per hour based on the activity I am engaged in and my body etc..

So what made me take pause is when to start the replenishment process. Let's say the rate is 240 cal/hr and the event is 3 hrs. Theoretically the muscle glycogen supply should last for approximately 90 minutes of the activity. Obviously I don't want to wait until that mark to start replenishing because it takes a while to consume and assimilate 240 calories worth of substance.

Is it best to start the replenishment clock ticking say once settled into the race, maybe 10-15 minutes? Or do I go an hour, leaving hypothetically 30 minutes of muscle glycogen supply, and start the 240 calorie intake cycle? In the case of a running event where carrying nutrition is more difficult, this would change the number of gel packs etc that had to be carried. Thanks for clarifying.
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Re: Timing of caloric replenishment

Postby steve-born » Thu Sep 22, 2011 9:44 am

Hello rbrnut -

You ask a great question! While muscle glycogen is indeed the first-used fuel when exercise begins, it is not the only fuel the body will use at the onset of exercise. In other words, while muscle-stored glycogen is the primary fuel for the first 0-30 minutes (and perhaps upwards up 60 minutes), blood glucose from ingested calories - as well as the calories from body fat stores - will also be used during the first hour. At an aerobic pace (VO2 MAX 30%-65%), the shift to primarily using calories derived from body fat stores occurs somewhere between that 30-60 minute mark, and it increases the longer you go... it's estimated that approximately 50% - 67% of your calorie needs will be fulfilled via the calories from body fat stores once you hit the 2-hour-and-beyond point.

What has always worked best for me was to start replenishing calories somewhere between 15-30 minutes after commencing exercise. That's when I start feeling comfortable (muscles are warmed up, blood's flowing smoothly, etc), and that's when my stomach says "OK, I'm ready to take on calories."

Now, you could probably extend that out to 60 minutes without any issues but I would personally err on the cautious/conservative side and start the refueling process at some point within the first 30 minutes after beginning my workout or race.

I hope this helps!

Sincerely -

Steve Born
Fueling Expert
Event Sponsorship Coordinator
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