Scientifically calculating absorption rates during racing

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Scientifically calculating absorption rates during racing

Postby hammer_user » Tue Feb 14, 2012 6:35 am

I seem to bonk every race at the 8 hour mark, and damned if I can get across the line before that. No cramps, no fatigue; it's just that I have to stop running, and start walking.

I can only enter one Ironman race per year, and training just doesn't simulate race conditions.

Is there a way of scientifically determining the maximum calories, water, and salts one can absorb in various race conditions?
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Re: Scientifically calculating absorption rates during racin

Postby steve-born » Tue Feb 14, 2012 12:01 pm

Hello hammer_user -

Let me start by saying that I agree with you 100% that it is impossible to replicate an Iron distance triathlon (or pretty much any race for that matter) in training. I used to compete in ultra cycling races (500+ miles) so there was simply no way I could ever come close to being able to replicate my races in my training.

You asked the question: "Is there a way of scientifically determining the maximum calories, water, and salts one can absorb in various race conditions?" My answer is that it may be possible but it is highly unlikely. The reason for that is because:

1) Everyone's physiology (their biological predisposition) is different; we're all "experiments of one" so to speak. In The Endurance Athlete's GUIDE to SUCCESS ( we provide some science-based parameters for fluid, calorie, and electrolyte intake. However these are not "set in stone" figures/recommendations; they are best used as starting points from which you can tweak - via thorough testing in your training - to determine what works best for you and your unique personal physiology.

2) There are a number of variables - the athlete's weight, their fitness level, the weather conditions, how well or poorly the athlete is acclimated to the weather, and more - all of which make it difficult to determine, at least with a high level of accuracy, precisely how much fluid, calories, and electrolytes a given athlete will need under a a given set of circumstances.

With that said, what do we know when it comes to calorie, fluid, and electrolyte intake?

CALORIES - when it comes to calories, the average size athlete (average being about 160-165 lbs) can effectively return to the energy cycle 4.0 - about 4.7 calories per minute, or 240-280 calories an hour. Of course, lighter weight athletes will not need nearly that many while larger athletes will most likely be able to assimilate a few more calories (perhaps in the 300-325/hour range).

FLUIDS - When it comes to fluid intake, there has been a ton of research done, mainly by Dr Tim Noakes, Dr Ian Rogers, and Dr Ian Harrison. I personally like what Dr. Rogers once wrote about hydration: "It is important to realize that longstanding advice about appropriate fluid intake for exercise was formulated on research done on much shorter events when the 'limit of human endurance' was much less. The applicability of this to longer events is questionable. The American College of Sports Medicine in its position statement, currently recommends a fluid intake during exercise of 600-1200 mls/hr. The fluid intake of most of the reported cases of exercise-associated hyponatremia has been at the middle or upper end of this range challenging this as an appropriate fluid intake. A more realistic intake is likely to be 500-750mls/hr. While the old mantra, 'If you don't drink you die' is not yet dead, it has certainly been challenged. We can no longer assume that excess fluid taken during prolonged exercise will just be passed out in the urine. Like most things in life, balance is the key and the balance is likely to be at a fluid intake not much above 500 mls per hour in most situations, unless predicted losses are very substantial."

What he is saying is that under most conditions most of the time, the majority of athletes will stave off dehydration - and prevent the problems associated with overhydration - with an intake of 500-750 ml of water (about 17-25.5 ounces/hour). We have found that many athletes benefit from just a couple ounces more; hence, our "28 ounces per hour" upper limit suggestion. Look closely, though, at the last thing Dr. Rogers says -- "... unless predicted losses are very substantial." In a race that's contested in hot-weather conditions, and especially if you're not terribly acclimated to those conditions, you know that "predicted losses" are going to be very substantial. That doesn't mean that you can replace all of the fluids that you're losing but it does allow you to increase your fluid intake above the normally suggested amount. Therefore, if the weather conditions are going to be very hot (and again, if you're not acclimated to them), it is most certainly feasible - recommended even - that you increase your fluid intake to 30-or-more ounces per hour. However, if you do so you MUST increase the number of Endurolytes that you're taking so that you don't have issues with overly diluted serum levels of sodium and other electrolytes, (hyponatremia).

ELECTROLYTES - This is arguably the most difficult component of fueling to get dialed in. By and large, we know what the upper limit is for fluid and calorie intake. Electrolyte intake? It's all over the map and all of the earlier-mentioned variables really come into play when determining the answer to "What do I need to replenish in terms of electrolytes?"

One example of the wild variations in electrolyte intake is a female athlete we have sponsored for years and years. Prior to the Western States 100-mile run, she had a complete blood profile done, one that included her pre-race electrolyte levels. During the race she consumed 1 Endurolytes capsule per hour... just 1 per hour. She ended up winning the women's division (beating most of the men in the process) and had another blood test/profile done. Amazingly, the results of her pre-race and post-race blood work showed her electrolyte levels to be almost identical. Not that's incredible!

So she's on one end of the spectrum. On the other end is an athlete I know (a great road cyclist) who, due to his biological predisposition, will start exhibiting cramping issues unless he takes 5-6 Endurolytes per hour, even in mild conditions. That's highly unusual so he's pretty much on the other end of the spectrum. The rest of us fall somewhere in the middle of those two extremes.

Fueling in General
It's crucial to keep in mind that the goal of fueling is to postpone fatigue as long as possible. It is NOT to try and replace "X" out (what you're losing during workouts or races) with "X" or "near-X" back in. The fact is that we can't replenish our bodies with the same amounts of fluids, calories, and electrolytes as we're losing. It'd be awesome if we could replace "X" out with "X" back in... theoretically we would extend exercise performance - at least from a fueling standpoint - to a level where fatigue wouldn't rear its ugly head for a long, long, long time. Heck, if we could replace all of the fluids, calories, and electrolytes we're losing in equal amounts, we may never tire!

Unfortunately, it just doesn't work that way. Dr. Bill Misner states it very clearly and eloquently I think when he says: "The human body has so many survival safeguards by which it regulates living one more minute, that when we try too hard to fulfill all its needs we interfere, doing more harm than good. If I replace all the fuels I lose at the rate of 700–900 calories per hour, I bloat, vomit, present diarrhea, and finish the event walking or at an aid station. If I replace all the fluids lost all at once, I end up in the emergency tent with an IV for dilutional hyponatremia. If I replace all the sodium my body loses at the rate of 2 g/hour, I end up with swollen hands, eyes, ankles, feet, and noticeably labored exercise, or hypernatremia–induced bonking."

"At an easy aerobic pace, the rate of metabolism increases from a sedentary state to a range of 1200–2000%. As a result, the body goes into 'survival mode' where blood volume is routed to working muscles, fluids are used for evaporative cooling mechanisms, and oxygen is routed to the brain, heart, and other internal organs. Interestingly, it is NOT focused on calorie, fluid, and electrolyte replacement, as some of the 'experts' advise."

Now, with all that said, here are our general recommendations for fluid, calorie, and salt replenishment:

Fluids: 16-28 oz/hour
Calories: 240-280/hour
Sodium Chloride (salt), as part of a full-spectrum electrolyte supplement: 100-600 mg/hour (1-6 Endurolytes)

This is what works for most athletes under most conditions most of the time. Again though, these are just general recommendations, they're not "set in stone" amounts, though they are good starting points. Bottom line is that you have to test everything in training thoroughly - under a variety of conditions - to determine what works best for you.

Aside from improper fueling, there are so many possible reasons as to why one bonks during a race so it's hard to cover them all... there really are so many possibilities. I'll touch on a few that I think are the primary culprits.

1) Not "refilling the tank" with fuel (such as Recoverite) or fuel ASAP after all of your workouts leading up to a race. When athletes don't make the effort to replenish their bodies within the first 30-60 minutes after their workouts (the sooner the better) they miss out on the opportunity to store more minutes of glycogen in the muscles. Muscle glycogen is the first fuel your body will use when you start a workout or a race so it seems obvious that you'd want as much of it available as possible.

In the recovery article in The Endurance Athlete's GUIDE to SUCCESS we write:

When you begin a workout or race, the primary fuel your body uses for the first 60-90 minutes or so is known as muscle glycogen, a glucose polymer that contains tens of thousands of glucose units arranged in branched chains. As your stores of muscle glycogen become depleted, your body switches over to burning fat reserves along with carbohydrates and protein consumed during exercise. You've only got a finite amount of this premium fuel, muscle glycogen, but its importance can't be overstated. In fact, several studies have shown that the pre-exercise muscle glycogen level is the most important energy determinant for exercise performance.

Needless to say, to have a good race or workout, you need to start with a full load of muscle-stored glycogen; athletes who have more of this readily available fuel in their bodies have a definite advantage. The good news is that you can substantially increase your glycogen storage capacity through the process of training and replenishing. Here's how your body does it: Along with insulin, which regulates blood sugar levels of ingested carbohydrates, an enzyme known as glycogen synthase converts carbohydrates from food into glycogen and stores it in muscle cells. This also drives the muscle repair and rebuilding process. However, to maximize the recovery process, you need to take advantage of glycogen synthase when it's most active. Carbohydrate replenishment as soon as possible after exercise, when the body is most receptive to carbohydrate uptake, maximizes both glycogen synthesis and storage. Glycogen synthesis from carbohydrate intake takes place most rapidly the first hour after exercise, remains fairly active perhaps another hour, and then occurs at diminished levels for up to six hours longer. Researchers at the University of Texas at Austin demonstrated that glycogen synthesis was highest when subjects were given carbohydrates immediately after exercise. Depletion followed immediately by carbohydrate intake yields the maximum glycogen resupply.

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My position is that if you REALLY want to "carbo load" it is NOT what you consume in the week before the race and it is NOT what you consume the night before the race. True "carbo loading," in my opinion, is what you do in the 0-60 minutes after all of your workouts in the weeks and months leading up to a race. If more athletes would simply "refill the tank" ASAP after all of their workouts in the weeks/months leading up to a race they would have an absolutely huge and undeniable advantage over those athletes who either blew off post-workout refueling and/or waited too long.

2) Not resting enough in days leading up to a race. In an article regarding how to have a successful half or full iron distance triathlon (email me at if you'd like a copy) I wrote:

You will not be able to positively influence your fitness level in the days leading up to the race; however, you can negatively impact your race by training during that time (training meaning anything of significant duration or intensity). As well-known coach Jeff Cuddeback states, "The week of any event of this duration should be all about resting up and topping off your energy stores. Training is done to keep the engine lubed and tuned up, nothing more. If you think you're going to further your fitness through training the week of your key race, you're sadly mistaken. If you are the type to train right up to the event, you will almost certainly under perform.”

Best performances in long-duration events are achieved by getting to the starting line well rested rather than razor sharp. In doing so, you may find yourself not hitting on all cylinders during those first few minutes. In fact, you might even struggle a bit at the beginning of the race. However, your body will not forget all the training you've done and it will absolutely reward you for giving it the time it needed to "soak up" all of that training.

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I tend to think that many athletes overcompensate in the days leading up to a race by training instead of resting (I know I've certainly been guilty of that). We're so afraid that we're going to lose all of our fitness that we feel inclined to train when our body is begging us to rest. A friend of mine refers to this as "taper tantrum" which I think is spot on.

3) Eating a pre-workout meal or pre-race meal at the wrong time. I discuss this thoroughly in the article "Proper Fueling - Pre-workout & race suggestions" in The Endurance Athlete's GUIDE to SUCCESS. In a nutshell, what happens when you eat within three hours of exercise that's in the 60-minute-or-longer range is that your muscle glycogen stores get burned much more rapidly. It took you many weeks of post-workout refueling to accrue that 60-90 minutes of muscle glycogen. You want to use it as efficiently as possible come race day; however, you will accelerate the rate at which your body uses its finite stores of muscle glycogen - effectively negating what took you weeks to accomplish - simply by eating at the wrong time. BOTTOM LINE: For workouts and races lasting longer than 60 minutes (perhaps up to 90 minutes at the most), refraining from calorie consumption for the three–hour period prior to the start is crucial because you want to preserve your glycogen stores, not accelerate their depletion.

4) Going out too fast at the start of the race and/or not pacing yourself properly during the race. This is kind of a no-brainer. If you go out too hard at the start of the race, chances are you're going to have difficulty come the latter stages of the race. To use an analogy, you only have so many "matches" available... you don't want to burn most-to-all of them at the start of the race, leaving you with little-to-none as the race progresses into its latter stages.

When I competed in the Race Across America I tried to remember "This is going to be a long, long race, and by the time I get halfway through Texas, California is going to seem like it was a month ago." I didn't want to dawdle during the first part of the race but I also didn't want to "burn all my matches" either, knowing I still had a long way to go. When it comes to an iron distance triathlon, I can only imagine how painful it would be to try and do a marathon if you've just put the wood to yourself during the bike portion.

If you go out too fast in a long-duration race, you will blast through your glycogen stores very quickly... that's performance-inhibiting in my opinion. If you go out at a sensible pace you will minimize the chances of bonking, which means that you'll not only finish the race, chances are you're going to finish it strongly. Of course, you don't want to finish a race knowing that you still had something "left in the tank"... you want to finish a race with the tank near empty. Conversely, you don't want to "empty the tank" halfway through the race either... that's only going to make the rest of the race a miserable experience. Pacing yourself properly, staying disciplined enough to go as hard as you know is sensible and right for you (forgetting about what others may be doing), is definitely a way to help prevent bonking.

I now realize that I've basically written a novel but I hope what I've written will be helpful to you. Again, if you'd like a copy of my article "Tips for a Successful Half or Full Iron Distance Triathlon" (it's basically an easy-to-read primer... nothing too in-depth) simply email me at and I'll be happy to forward a copy to you.

Sincerely -

Steve Born
Fueling Expert
Event Sponsorship Coordinator
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