Ever Important Water

Hi Everybody:

Here is a coaching tip:

Water accounts for about 70% of your body weight.

Losing a tiny fraction of this water will cause performances to drop.

Without getting into details here, the body’s cells need water for basic function.

For the runners in our Club, here is some science for you to think about:

Average adult at rest consumes about 0.25L of Oxygen per minute or 70 Watts of heat output.

When running a 6 minute mile pace, oxygen consumption rises 16-fold to over 4L/min.

The amount of heat generated increases in excess of 1100W!

This discussion will not get into ambient temperature effects.

Bare in mind the evapourative cooling (sweating) must occur.

A 70kg runner, in warm conditions, burns about 1000 kcal/hr.

In order to facilitate the extra heat removal, the body will lose about 1.5L of water (H2O)/hour.

So, in hot conditions, runners can easily lost 2L of water per hour.

A loss of just 2% of body weight (or 1.5L/hr @70kg) can cause a significant drop in performance.

Take some time to understand what your body needs under the duress of racing during tough training sessions.

You can control the outcomes best if you prepare for many possibilities.

Just putting miles in on the trainer, on the roads or in the woods is not enough.

Take some time to listen to that beautiful machine that makes it all happen.

Don’t forget your screen – it is that time of year too where we can get sunburned because so many of us forget that we do get HOT summers despite the rains and snows of the winter months.

Happy trails,

Greg Cushing

PS: A bit more science for you:

Water balance at rest
Excerpted from Physiology of Sport and Exercise, Seventh Edition, by W. Larry Kenney, PhD, Jack H. Wilmore, PhD, and David L. Costill, PhD

Under normal resting conditions, the body’s water content is relatively constant: Water intake equals water output. About 60% of our daily water intake is obtained from the fluids we drink and about 30% is from the foods we consume. The remaining 10% is produced in our cells during metabolism (recall from chapter 2 that water is a by-product of oxidative phosphorylation). Metabolic water production varies from 150 to 250 ml per day, depending on the rate of energy expenditure: Higher metabolic rates produce more water. The total daily water intake from all sources averages about 33 ml per kilogram of body weight per day. For a 70 kg (154 lb) person, average intake is 2.3 L per day. Water output, or water loss, occurs from four sources:
Evaporation from the skinEvaporation from the respiratory tractExcretion from the kidneysExcretion from the large intestineHuman skin is permeable to water. Water diffuses to the skin’s surface, where it evaporates into the environment. In addition, the gases we breathe are constantly being humidified by water as they pass through the respiratory tract. These two types of water loss (from the skin and respiration) occur without our sensing them. Thus, they are termed insensible water losses. Under cool, resting conditions, these losses account for about 30% of daily water loss.

The majority of our daily water loss—60% at rest— occurs from our kidneys, which excrete water and waste products as urine. Under resting conditions, the kidneys excrete about 50 to 60 ml of water per hour. Another 5% of the water is lost by sweating (although this is often considered along with insensible water loss), and the remaining 5% is excreted from the large intestine in the feces.

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