Cold water myth?

[sillygrendel]

I've seen in a number of places the assertion that one of the reasons you get so hungry/tired after spending all day in the water (diving, swimming, etc) is because you spend a great deal of energy heating up the water.

Is this true?

I know the body produces heat naturally and will produce more heat if you move around more. The main methods I'm aware of about how the body regulates heat have to do with shunting blood either to the core (cold) or the extremeties (hot).

If I kept my activity level the same in both 98.6 degree water and 70 degree water would I burn more calories in the cooler water?? (excluding the case where you would be so cold you would shiver -- which would happen eventually)

How is this accomplished?

 

[chrispete]

You lose heat in water many times faster than you do in air. (water is a much better conductor of heat than air is) In 70 degree water, the water will wick away heat at a rate that is faster than your body can reheat itself (i.e. you will burn more calories trying to keep yourself warm and after a long exposure would go into hypothermia) - in 98.6 degree water, you should not lose heat as the temps are already equalized between you and the water - thus your body will not have to work hard to maintain your core temp.

 

[sillygrendel]

I know that you lose heat much faster in water.

If you're not cold enough to shiver. (The bodies response to try and produce more heat through muscle action) How does your body 'work harder' to keep you warm? Does the vasoconstriction take energy? I know it conserves heat but does it also produce heat?

Can your body increase its metabolism to burn more calories and produce more heat? What are these calories burned to do? Where is the heat produced??

Or is it that in cold water you will unconsiously move around more, thereby generating more heat?

 

[Rick Murchison]

I think I see the problem with understanding here - there is much of metabolism that doesn't go to muscular activity. The body uses fuel to maintain body temperature as well as to perform tasks with muscles, run hormonal systems, produce digestive juices, solve equations, etc, etc, etc... The answer to your question is "yes, the body burns more fuel - uses more calories - to heat up the water that comes in contact with it. Yes, you burn more calories in colder water, just to maintain body temperature." Muscular activity becomes involved when the normal "heat producing only" processes fail to keep up. This is called "shivering."
Rick

 

[sillygrendel]

I understand that the body produces heat in all of the myriad of chemical reaction that occur to do all of those things.

Part of the reason I posted this here is that I was asking a doctor about it the other day and his response was:

"How? Where does the heat come from? Where is this energy burned if you're not more active?"

Well... I don't have an answer! Does my body produce more stomach juices because its cold to make me warmer? Do my mitochondria work overtime to pump more protons? Do my toenails grow? Does my IQ raise a few points in cold water?

All of the above?

 

[Rick Murchison]

One of the body's metabolic processes is not associated with any other activity than heat production. Purely "burning" carbs to get heat. Nothing else. Just heat. Just Glocose + Oxygen to get Carbon dioxide, water and heat. Just like you burned it out in the open air, except enzymes are involved - but no action, no juices, no hormones, no nothing other than heat. It's complicated and regulated tightly - it can be increased to fight disease (fever) or to help maintain body temp in colder water or air. It can be shut down when not needed. The body doesn't "do" anything with the metabolic burning of the sugar other than produce heat. The only by-products are carbon dioxide and water and heat. That's all. The enzymes end up the same as they started.
Rick

 

[sillygrendel]

Thanks

 

[The Iceni]

sillygrendel once bubbled...
If I kept my activity level the same in both 98.6 degree water and 70 degree water would I burn more calories in the cooler water?? (excluding the case where you would be so cold you would shiver -- which would happen eventually)

How is this accomplished?

Yes, you would burn more calories in colder water but. .

As warm blooded creatures we produce heat by several mechanisms to maintain core temperature when exposed to cold as well as preventing heat loss or gain in low/high temperature environments. The body reflexly generates heat by simply burning those calories in the liver. In addition, shivering generates heat from muscle by burning even more calories. (Rigors are an extreme form of shivering employed by the body to produce the high fever needed to fight infection.)

In order to keep warm heat losses must not exceed heat gain.

In water the mechanisms that the body uses to prevent heat loss (such as periperal vasoconstruction and the erection of hairs ) and the internal generation of heat energy cannot cope with the twenty-fold increase in heat loss to water.

Even if you exercise vigorously in cold water the body cannot produce enough heat to prevent hypothermia developing unless the diver (or the shipwreck casualty) wears protective clothing.;- The vast majority of shipwreck casualties die from hyopthermia.

We do not rely on our body hair, we wear clothes to keep us warm on land. Wet suits, semi-dry suits and dry suits of varying efficiency do this for a diver. I keep as warm as toast in the North Sea in winter wearing my membrane dry suit with it's thick undersuit, whereas I would be dead from hypothermia within a very few minutes without it.

This will also be the case, even in tropical waters, in time.

It is not the water temperature that matters or indeed the level of activity, so much as the insulation used by the diver to reduce the considerable conductive heat losses to water.

I hope this adds more to the answers already given.

 

[Santa]

Loose weight ... dive naked ;0)

Santa