I don’t get it. My HRM (Polar S510) says I use about 840kcals an hour (avg) during sub race pace (thats avg for bk rn). So say it’s an even 900kcals at race pace on race day. How the hell am I going to replace those?
I mean during the course of a 6hr for my first HIM that’s 5400kcals. Do I have to carry a grocery bag w/me on the bike 1)to make up for kcals lost on the swim 2)those I’m burning on the bike 3)store up so I don’t bonk on the run (my weakest disc.)
Or do I just take kcals at aid stations to take on 300-400 which I’ve read is the most a normal person can absorb anyway, stay hydrated and hope for the best. I know about the 2000kcals or so stored in our in the liver and muscles, but that is still a shortfall of 1000kcals if I am able to absorb 400kcals/hr. Do I just need to chill is 1000kcals not enough to notice.
I realize I need to take the HRM calculated kcals burned with a grain of salt (sodium another concern for a salty sweater) but even if it’s off by a little 1000kcals or thereabouts seems like a lot to this neophyte.
6 % body fat on a 150 lbs perrson = 9 lbs fat * 3500 kcal = 31 500 kcal. that ought to do it…
you’ll never be able to take up what you expend during a race. you probably can’t absorb more than 60 g of carbohydrates per hour. speaking of which, keep doing that: if you’re low on carbs, you can’t metabolize fat very well, ie, you bonk.
also, 900 kcal is pretty high for an HIM race pace unless you’re 6’6", 235 lbs. may be that your polar is overestimating.
You may want to consider having a few training sessions (particularly longer) consuming less calories. Undoubtedly for longer races your body must burn fat stores. Using fat as an energy source is not an easy thing to do, and your body must learn to do it efficiently. I’m not saying you want to do this every time, however, I think it’s good to train off of fat every once in a while, as this is not an easy thing for the body to do.
50-80%? i think you’re overestimating by quite a bit, but it will vary considerably depending on intensity. the balance of substrate utilization for someone at the front end will be quite different from somebody who walks most of the run.
regardless, the general idea is correct. fuel will be derived from liver and musscle glycogen stores, ingested food, and stored fat.
i agree that most of the polar estimates for caloric expenditure that people report seem to be too high.
I hope that these basics of nutrition and biochemistry will help.
Everyone is slightly different in terms of their needs
Your body has a significant store of carbohydrates before you start a race. If you have properly maintained your stores and topped up a bit with some carbo loading your should be able to go at roughly 70 - 80% V02 max levels of exertion for 2 hours without taking anything in - but then you will bonk. So if the event is much longer than 2 hours you need to take something in. I say this, because it’s illustrative of not only that you need to take more in, but that you also have these stores.
3.The stomach can only absorb so much carbohydrate in fixed period of time and at the right concentration( studies have shown it’s around 7%)
The general rule of thumb is that you need to take in roughly 250 calories/hour give or take for extended time events. How you get this in is really up to you and you need to figure that out on your own. People have done well doing an entire IM on Gatorade, while others swear by peanut butter and jam sanwiches!
Bottom line is that you don’t need to replace each hour the actual number of calories that you are burning.
As a very basic rule of thumb I’d base calories burnt on the distance. Again very genericaly it doesn’t matter whether you’re going fast or walking the caloric burn is roughly the same per distance at teh same weight. This obviously is not nearly 100% accurate and is much more variable in the swim and bike than on the run.
As Fleck pointed out nutriotional needs and uses is highly variable from person to person. I’m guessing that your total caloric expentiture for the race will be closer to 4400 rather than 5400. Figure roughly 30-50% will be provided by fat that leaves you with only 2600 or so that is glycogen or glucose. Assuming it will take you 6hrs and you can take in 250 calories and hour you’re only at a 1100 glucose, glycogen deficit, well within body stores at the begining of the race.
Of course the above is completely a Wild @ss guess…but is meant to put your mind at ease.
Ok that does help. Thanks Fleck and Mjuric and everyone else. I read stuff about replacing cals on the bike and so I started doing some numbers base on info I had and was like holy crap. On training rides I go with a bottle of carb drink (Accelrade) and a bottle of water. Wash my Gu down with water and drink the carb drink otherwise. It has worked on long rides and bricks. I will just have to do a practice HIM to see if it will work on a larger scale.
