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Cool weather dehydration during kayaking

Cool weather can increase your risk for dehydration which is usually associated with hot weather. A kayak or canoe paddler will often force their body to work harder with layered clothing; loosing respiratory fluid through labored breathing and quick sweat evaporation in cold dry air.

Dehydration isn't an exact science. By monitoring fuid intake and output; a paddler can prevent performance loss, rapid onset of fatigue, low endurance and elevated core temperature. Remember to listen to your body's feedback mechanism, it’s smarter than you are most of the time. Heart and respiration rates will increase to compensate for decreased plasma volume and blood pressure, while body temperatures rise due to decreased sweating. Feeling of grogginess, headaches, irritability, thick saliva, or nausea, may be an indication of dehydration.

When our bodies think about water, the amounts usually involve quarts and gallons, not ounces. Humans attempt to regulate a steady-state of temperature (homeostatic) by sweating. By simply walking around we produce 0.25 to 0.5 quart of sweat per hour, vigorous activity cranks it up to 1.5 quarts or more depending on a variety of factors. The human body sheds heat by a combination of perspiration evaporation , heat convection/conduction in the surrounding air, and thermal radiation.

How much water is enough becomes an extremely tough generic question. Each person is an individual with various factors such as age, physical condition, environment and so on. The human body can range anywhere from 55% to 78% water depending on body size. Water serves as a lubricant for joints, is the basis of saliva, and it helps provide efficient transport of nutrients between cells of the body.

Water is quite simply a combination of hydrogen and oxygen aiding our blood supply and bodies. When blood enters the end of a capillary, it is still under pressure produced by the contraction of our hearts. A substantial amount of water and some plasma proteins filter through the walls of the capillaries into the tissue space. High school biology classes taught us about the diffusion of gasses and osmotic water pressure between cells.

During vigorous exercise capillary beds in the skeletal muscles open, shorting blood supply to the organs. The increased blood supply goes to the skin for heat dissipation produced by the muscles.

Blood Flow ml/min

                                         At Rest                  During Strenuous Exercise
Heart ................................ 250...........................750
Kidneys.......................... 1,200..........................600
Skeletal Muscles............. 1,000....................12,500
Skin ................................... 400.......................1,900
Organs........................... 1,400.........................600
Brain......................... .........750.........................750
Other............................... ...600.........................400


Total ............................... 5,600...................17,500

Notice the kidneys decrease output under the load of vigorous exercise. You may notice that urination often takes place only after an extended workout has ended, and the body comes back to a resting heartbeat.

About 78% of the molecules in dry air are nitrogen, 21% of the molecules in dry air are oxygen (O2). The final percentages of dry air is a mixture of other gas molecules. For any gas, at a given temperature and pressure, the number of molecules present, in a particular volume, is constant  - (see ideal gas law)

Warm humid air is less dense than cold dry air because a molecule of water at 18 microns is less massive than either a molecule of nitrogen at 28 microns or a molecule of oxygen at 32 microns.

So when water molecules are introduced into a volume of dry air, the number of air molecules in the volume must decrease by the same number, - if the temperature and pressure remain constant.

The addition of water molecules, or any other molecules, to a gas, without removal of an equal number of other molecules, will necessarily require a change in temperature, pressure, or total volume.

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