Water preparation on desert hiking

I served in an Army that tried that. "Water discipline" was used to try and make soldiers get used to using less water.

It failed miserably: People died or got seriously hurt, there was no visible benefit, and the habit was abandoned.

posted over 4 years ago

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6mo ago by Michael‭

Rsf‭

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Summary: Heat adaptation (i.e. being able to do physical excercise in the heat) has a number of mechanisms, but among them the "water-related" mechanisms rely on having and needing, i.e. using more water.

Heat adaptation increases the body's total water volume, so in that sense it improves water retention. Still, this can only be achieved by drinking more water rather than less.

Starting (slightly) dehydrated is not a good idea as it basically cancels these improvements. The only way to adapt to low availability of water is to reduce the need for sweating - which basically translates to avoiding physical exertion and staying in cool shaded places.

For a given amount of physical excercise in the heat, there is no healthy way around supplying sufficient water to allow heat dissipation by sweating.

There are 3 major ways how water leaves our bodies:

1. sweating: main purpose here is to use evaporation heat to get rid of excess heat, and under physical exertion in the heat this is by far the major excretion of water for humans. We can sweat several l/h or 10 - 14 l/day. Heat of evaporation is 2257 kJ/kg for water, so sweating 2 l/h means up to 1.25 kW cooling power (minus losses due to dripping) - which corresponds quite well with more than 1 kW heat power output during strenuous excercise.

   To make clear how important this is, here's a back-of-the-envelope calculation. For a 70 kg human with specific heat capacity of 3.5 kJ/(kg K), 735 kJ are needed to increase body temperature from normal 37 °C to 40 °C (heat stroke, which is life threatening also for athletes, soldiers, etc. [the scenario of the question also precludes adequate treatment] and has a high risk of permanent damage for survivors). The same amount of heat can be dissipated by evaporating 325 ml of water, an amount of sweat an adult can produce (if the necessary water is available) in a few minutes. It is also an amount of heat that can be produced by strenuous excercise within 10 - 15 min.

   There are AFAIK only 2 healthy options to reduce body water loss here: use non-drinkable water for evaporation (soak shirt in puddle or sea, probably not an option in the desert) or produce less excess heat. Possibilities are:

   • do physical exertion when it is cool, so larger parts of the produced heat are needed/used to keep up body temperature

   • stay in the shade/take your shade (clothing, umbrella) with you

   • training does not only increase strength/endurance but also leads to better technique thus spending less physical power to achieve the same result. This means also less excess heat and thus less water loss via sweat.

   • We can also train our sweating as part of heat adaptation. However, this does not preserve water but rather allow us to sweat more (see below)

2. evaporation in lung, ..., and nose: our lung works best with warm and moist air, so the nose (and further airways) moisten (and warm up) dry air we breathe. If it's cold, the nose can get back some of that water when cooling the outgoing air. If it's warm outside, the added moisture will stay in the air and be lost, and I don't think much can be done about this (other than breathing less = less physical exertion).

3. excretion as urine via the kidneys: there are 2 aspects to this.

   The kidneys need to excrete a certain amount of water in order to get rid of the waste material that needs to be excreted. Jan’s response already explained that for example excretion of urea needs a lot of water - so yes, while in the desert you'll want to get your energy from carbohydrates (that prodce some water when metabolized) rather than protein.

   The kidneys also regulate total volume, i.e. if there's excess water, they'll happily excrete that as well. This is the background for your if you drink a lot of water, it's not retained. However, I wrote "happily" on purpose: the kidneys need to work harder to excrete highly concentrated waste (or fail) compared to lower concentrations.

   Thus, if you don't get sufficient water, the kidneys will excrete less urine. However, the amount of water that can be saved this way is limited: normal excretion is roughly 1.5 l urine/day (varies about ± 0.5 l from person to person, < 400 ml and > 2.5 l get "medical names"). So the total normal daily urine production is only a fraction of the normal sweat production under physical exertion in the heat.

Heat adaptation

According to the review Périard, S. Racinais and Sawka: Adaptations and mechanisms of human heat acclimation: Applications for competitive athletes and sports, Scand J Med Sci Sports 2015: 25 (Suppl. 1): 20–38,

heat adaptation leads to a number of changes which are relevant for this question:

• rest body core and skin temperatures are decreased (it seems to be an open question whether higher core temperature is tolerated during excercise)
  The lower resting temperature would give a bit more "buffer" agaist the heat produced during excercise - but this is quite limited, see calculation above.
• sweating: starts earlier at lower onset temperature and is increased in its rate. The sweat has lower salt concentration.
• skin blood flow increases at lower onset temperature and is increased in its rate.
• Thirst is improved: without heat acclimation, they report that thirst does not fully replace the water losses. With heat adaptation, one does drink adequately more water.

• Increase in total body water (2 - 3 l) and plasma volume (usually 4 - 15 %, range 3 - 27 %), though that varies a lot person to person. The review hypothesizes that the lower end of observations may be for athletes who were already in a status of body water/plasma expansion at the onset of the respective study.

  The review argues that this increased water volume and plasma expansion helps in several ways: it is very important for the increased cardiovascular stability (which improves a lot during heat adapatation) and it may serve as additional buffer against dehydration. Also, low body water/plasma volume when dehydrated during excercise worsen the increase in core body temperature (possibly lack in volume doesn't allow vasodilation and thus heat transport to the skin where it is dissipated by evaporating sweat as well as the rate of sweating is restricted)

  The proposed prepare-by-thirst-regime would directly counteract this adaptation effect, and you really want to fully profit from this increase in body water as this one effect alone results in 1.5 - 2 x as much added "capacity" to deal with heat strain than the hypothetical (or dangerous) effect of your kidney shutting down completely plus raising body temp about 3 °C combined.

• The review mentions that it has been hypothesized that permissible dehydration during a heat acclimation regime (which I read as: going into mild and temporary dehydration during excercise in the heat, but not over prolonged time such as days) may speed up the acclimation process, but they don't have studies observing this (publication bias makes it unclear to me whether this hasn't been studied or not finding the effect has not been reported). The above mentioned plasma expansion and total body water starts from day 1 and occurs over less than a week, anyways.
  In contrast, it is well established by studies that excercise in the heat triggers acclimation.

• After short-term heat acclimation, the body core temperature at heat exhaustion remained the same as before (39.8 °C), and also the heart rate did not increase much, but endurance improved. There is some indication that trained athletes with heat acclimation over many weeks can tolerate higher core temperature (up to 41.1 °C reported).

posted over 4 years ago

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cbeleites supports Monica‭

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This sounds to me like a bad idea because you don't want to go into the hike already a little dehydrated. My recommendation would be to go into the hike very well hydrated, and to drink a lot of fluids during the hike, and don't forget about electrolytes.

posted over 4 years ago

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Jason‭

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Water preparation on desert hiking?

It is almost impossible to training the body for hacking or trekking in the desert, especially if one is not use to it.

Heat acclimatization seems to be a much more beneficial way to prepare for the desert than what you are speculating would a good way to prepare: ”Lowering the water intake a few days before the hike a better approach to deal with the situation by adapting gradually to the extreme conditions?” Heat acclimatization for at least 10 days seems to be a better and less stressful way to go.

Even if one drinks lots of water, the desert can make you a victim of heat exhaustion in no time flat.

Always take more water with you than you think you may need. Avoid bringing alcoholic drinks with you as the tend to make one more thirsty and less hydrated.

The larger one one’s bodily frame and general weight are the more water one will require.

I remember reading the book, The Long Walk involving a trek through the Mongolian Desert and the group soon realized the need of having water in a desert that had little water in it. One of their greatest needs was also to keep as cool as possible and for this they regretted that no one could read the stares in the night sky in order to do the trekking more easily in the cool of the night rather than hike in the middle of the day when the temperature is at its’ highest. Foresight count for something in the desert.

The desert can be a brutal on the body and one’s system. It pays to know which plants in a desert retain some amount of water in case of an emergency.

Here are some tips for those interested in hiking in the desert .

• Avoid Going Hiking at Peak Heat
• Avoid the Desert in Summer – Try for Fall, Winter or Spring
• Hike or Backpack in the Desert at Night
• Find Shade During Peak Sun Hours
• Wear the Correct Clothing
• Wear Light, Breathable Clothing
• Hat, Sunglasses, Sunscreen Are Necessary for Hiking in the Desert
• Wet a Bandana or a Kool Tie
• Stay Hydrated
• Bring Enough Water
• Drink Water Before Your Hike
• Drink Gatorade or Electrolyte Water TIPS AND TRICKS FOR HIKING IN THE DESERT

posted over 4 years ago

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Ken Graham‭

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I have heard that if you drink a lot of water as a habit, the body doesn't do much retention.

That just means that your body will not retain excessive water.

Therefore, if you are preparing for a hiking in the desert where not much water will be available, is lowering the water intake a few days before the hike a better approach to deal with the situation by adapting gradually to the extreme conditions?

No. When you drink too little and become dehydrated, your body will start to inhibit sweating and urination, but you don't want to make yourself intentionally dehydrated before going to desert.

Can you improve water retention by diet?

Yes, to improve water retention, avoid high amounts of protein, which, when metabolized, produces urea, which drags water with it when excreted into urine. For example, eating 100 g of protein (100 g of cheese + a 120 g can of fish + a 150 g can of soybean + 500 mL of milk) can result in loss of ~800 mL of urine (NAP.edu).

Can you improve water retention by certain supplements?

Probably not in a hiking-through-desert scenario. Glycerol and hypertonic beverages high in sodium temporary (for few hours) increase water retention but do not decrease your water needs (Medicine and Science in Sports and Exercise).

posted over 4 years ago

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Jan‭

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