Adventures in exercise physiology: Tampa edition

Best I can tell, I lost about 1 pound of body mass during the Tampa Bay Marathon Swim. Actually – probably closer to 1.5 pounds, but we’ll call it a pound. Marathon swimmers often lose substantial weight over the course of a swim, but most of this is water loss that is soon regained. I estimate that I lost a little over a pound of body mass – that is, fat (and possibly some protein cannibalized from my muscles). For convenience, we’ll call it a pound of fat.

Some back-of-the-envelope calculations:

Losing a pound of fat requires an energy deficit of 3,500 calories. I consumed 2,800 calories during the swim. That puts my total energy expended during the 9-hour swim at 6,300 calories — 700 calories per hour.

This tells me a couple of things. First, my energy expenditure is higher than I expected. 700 cal/hr is the typical estimate for “vigorous” swimming – but this was my ultra-marathon pace. Second, I can probably experiment with raising my calorie consumption. I took 311 cal/hr in Tampa, but when I’m burning 700 cal/hr that puts me in deficit within, at most, 5.1 hours (assuming 2,000 calories pre-stored glycogen), and possibly as little as 3.8 hours (assuming 1,500 calories glycogen).

Jared, am I thinking about this the right way?

7 thoughts on “Adventures in exercise physiology: Tampa edition”

  1. I’d say that math is about right (of course all of this being theoretical) But I’d add the following thoughts:

    Your math of you “running out” of fuel at 5.1 hours is correct based on your burn/intake deficit of 389 cal/hr (700/hr burn – 311/hr uptake = 389 cal .. 2000 cal glycogen / 389 = 5.1 hours = you float and move no further). However as you say, its marathon swimming- and thats why your pace is important. You would only hit that absolute zero if you were swimming at a pace that was at high enough intensity to force your body to burn only glycogen. As your pace slows, your body has the ability to metabolize fat and is not limited to just using the readily available glycogen. If you did the deadman float your body can “keep up” with the low energy demand and exhausting your energy is not of a concern. Conversely, if you are swimming at a tempo pace, say, 1:10/100yd- you are working too hard for your body to effectively access your fat and ultimately you would have to stop. To put it in land based caveman terms (because after all, we humans aren’t designed to swim), you could WALK to Ohio tracking migrating buffalo on the “energy” (fat) that you have right now- but I bet you couldn’t RUN after that herd to the city limits.

    Lastly (because I’m getting the death stare from Shannon because we have to be at brunch) – increasing your consumption of cal/hr doesn’t guarantee your body can absorption. I think 300 is about right.


  2. Part 2 (from a cab)

    re: consumption/absorption

    from all the athletes nutrition profiles I have seen, 250-400/hr is the normal range. This can, of course, be “trained” over time. More correctly put, your gut can come to tolerate a higher rate of cal/hr- but you will still be limited by your gastric emptying. WHAT you put in your gut has a lot of bearing on your absorption rate as well. Higher quality products put a lot of focus on osmolality (lower = faster emptying). The trick for the manufacturer is to get the highest number of calories (with electrolytes, caffine or whatever else) while keeping the osmolality down to a tolerable level (under 300 mol).

    If your kayaker fed you chipotle every 20 mins you could put your consumption at 2000 cal/hr- but if your max absorption is only 350/hr you’d quickly have a problem.

    And last thought: all of this combined IS what your sport is about (at least physiologically). Balancing a pace that determines fat/glycogen usage with replacement through absorption. That, and swimming for 9 hours 😉

    Brunch time! (speaking of consumption)


    1. Jared, thanks. I find that terrestrial endurance athletes (such as yourself) tend to be much more sophisticated about nutrition than swimmers (for whatever reason). Just one of the reasons I’m glad to know you.

      Speaking of the sports drink industry… something I’ve been pondering recently is how swimming may differ from land-based activities in its nutritional requirements. One example that’s often discussed in the channel swimming community is that, in a saltwater swim you’re constantly ingesting sodium (via saltwater). Sodium is the primary component of the electrolyte mix in most sports drinks – and you really don’t need it. Also, especially in a cold water swim, fluid loss (and therefore electrolyte loss) is likely much less than when running or cycling.

      Triathlon and distance running are enormous markets compared to marathon swimming – so it makes sense that manufacturers would design sports drinks with those folks in mind. The question is: Are these drinks sub-optimal for swimming – and can we improve performance by changing the recipe?

      I know INFINIT offers customized recipes… the question is, what recipe to ask for?

    2. I’ve also been reading some research about how you can effectively raise absorption rate by mixing different carb sources, e.g., maltodextrin + simple sugars instead of just one or the other. I know higher quality products already do this, but I’ve devised a recipe that does it substantially less expensively. I’ll tell you about it sometime 🙂

      Hope you had a good brunch.

  3. The “terrestrial” endurance sports athletes are more savvy about nutrition because it is easier to drink/eat while running/biking vice swimming. Plus, despite all the stories about marathon swimming over the decades (centuries?), it really is rather new at this point.

    There are so many amateur marathoners out there versus amateur swimming marathoners, thus the companies have a bigger consumer base…

    Just thinking out loud

  4. Sounds about right to me. Once the water temperature is below the nominal range (30 to 34C) thermal radiation from a warmer body to lower body requires a greater energy input. I estimated about 800 cals per hour for the colder EC.

    There is also a maximum carb uptake per hour, (I thinks it’s 300).

    Best ratio for endurance is 4:1 carbs/protein but we’ve found problems with that practically on long swims. The protein most often comes from lactose (whey), which, when salt water is added through ingestion, many of the Channel group have reported causes slower digestion & protein uptake. I’ve been talking to a few people (non-swimmers) about alternatives and how to best optimise this for future swims.

    Extract from a discussion: “Waxy Maize starch is known for very fast gastric emptying. There is debate about whether or not it actually gets absorbed fast or not (it seems that the fast absorption is due to a compound which frequently gets extracted out of it; called vitargo or something). Fast gastric emptying is good in sports due to less chance of vomiting.Similar on those lines, casein protein is a fast gastric emptying rate yet a slow intestinal uptake rate. I would think that having a 4:1 blend of waxy maize starch:casein protein may prove interesting for being able to pass the stomach fast but stay in the intestines longer. The only problem is that both waxy maize starch and casein protein are very viscous when drinking it. If you keep the solute low it may rival some sort of pudding, although sludge would be a better word for it. not sure how your athletes would like this.”

    Part of the problem is that we tend to go with what have been proven to work, even though that may not the best way. And as you mention, we are a small study group, so changes happen very slowly, and based more on experience than science.

    1. @Donal This is excellent – thanks. I think I’ve heard 300/hr for carb uptake too, though I’ve also seen some recent research suggesting that uptake can be increased by mixing carb sources w/ different intestinal transport mechanisms. For example, see this and this.

      One thing I’ve wondered about in reading the Channel Group archives is whether electrolytes are truly bad in a long saltwater swim, or merely unnecessary. Mike Oram seems adamant that channel swimmers are overdosing on electrolytes, but don’t your kidneys expunge any excess minerals through urination?

      I also wonder if drinks containing free-form amino acids instead of full protein have the same problems re: digestion? I ask because some manufacturers in the U.S. are moving toward AA’s instead of protein in their endurance drinks. For example, 1st Endurance EFS (AA’s) vs. Hammer Perpetuem (soy protein). I know Dave Barra used EFS on his EC swim last year.

      On the other hand, EFS contains off-the-charts levels of electrolytes (which the cyclists love, I assume).

      Fascinating stuff re: waxy maize starch & casein protein. Will be interested to hear what comes of it.

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