More Fueling up

Did an hour long ride today at OD pace... 14.4 miles with an avg HR of 117

How much do you need to eat/ingest during a Half IM or IM race?

The first thing you need to know is how many calories are you going to burn? This is fairly easy to estimate with the right equipment. For example, my Suunto T6 measures my speed, distance and HR, combining that with my weight allows the Suunto software to produce a good estimate of how many calories I’m burning.

An article on Runnersworld.com (http://www.runnersworld.co.uk/news/article.asp?UAN=259) estimates that at a 10:00 pace (roughly what I’m shooting for on my run) someone my weight (150lbs) will burn 113 calories per ten minutes or 678 calories per hour.

Another online calculator (http://www.healthstatus.com/cgi-bin/calc/calculator.cgi) estimates that I would burn 684 calories per hour,

My Suunto says that running at that pace will cost me ~730 calories per hour whereas my expected Half-IM bike effort will cost me ~550 calories/hour, which doesn't seem right.

The second question is what percentage of those calories is coming from fat, carbs and protein. The lower your effort level, the higher the percentage of fat you burn. Fat is, for most people, practically an unlimited energy source. With 9 calories per gram of fat and 450 grams per pound, one pound of fat will supply you with 4050 calories of energy. That’s enough energy to keep me running for almost 6 hours, if only fat were burned and energy I don’t need to worry about replenishing during the race. Unfortunately, I’ll be burning more than just fat during my race, if I want to finish the run in less than 4 hours that is. Once you figure out how many calories you burn from fat, you’re left with the number of carbs used during exercise.

One final factor is that the average body can only metabolize 1 gram of carbs per minute during exercise. Using different types of sugars can boost this to 1.5grams/minute or 90 grams per hour. That’s 360 calories per hour. My current fueling plan has me taking in two 100 calorie snacks every hour and 3-4 drinks with 75 calories of carbs each which is 425-500 carb calories per hour on the bike, quite a bit more than I can absorb. Switching to something like Accelerade or Accel gel may allow me to get around the carbs cap and digest more calories. However, I don’t plan on eating nearly as much during the run

An aletrnate method is to take 1gram of carbs per kilogram of body weight each hour. My ~70kg mass would require 70 grams of carbs or 280 calories, which is well within the 360 calories per hour digestion limit and well within my fueling plan for on the bike and the run