The amount of fluid your body releases while exercising over a set period of time, at a specific intensity level, under specific environmental conditions.

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• Level of Exertion - the higher your intensity level, the more you will sweat.
• Temperature and Humidity - The higher the heat index, the greater the impact of fluid loss.
• Type of Clothing Being Worn - the lower the cooling efficiency of the clothing, the higher the sweat response.
• Conditioning and Fitness Level of an Athlete (Acclimation) - in general, the body of a well conditioned athlete is used to producing the sweat response (for cooling and temperature regulation) and begins this at a lower temperature than the non-conditioned athlete.
• State of Fluid Balance - as an athlete become more dehydrated, the rate of sweat loss decreases as does the athlete ability to regulate temperature.

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Replacing the fluids AND electrolytes is a very important part of maintaining a solid level of performance. Neglecting to do so, can lead to bad things like decreased performance and DEATH (Google Hyponatremia).

By knowing how much and how fast your body is getting rid of it's "water weight" you can properly re-supply to keep the body and mind firing on all cylinders.

Here are some of the other downsides of dehydration:

• Loss of neurotransmitters – Neurotransmitters are chemicals within the body that aid in the transmission of signals (across synapses) from our brain from one neuron to another.  They are released between small junctions in the pathway between the brain and your muscles.  In regards to exercise, they allow for muscle contraction and relaxation. With decreasing levels of these (calcium, sodium, and potassium are the big ones here) our muscles can’t release after contracting and we cramp. For anyone who has experienced cramping, this definitely decreases performance.
• Blood volume decreases – Sweat is often pulled from the plasma that makes up a 55% of our blood and helps to keep it flowing smoothly through our body.  When plasma volume decreases blood becomes thicker and your body must work harder to pump what blood is available through the body. If the body is working harder to pump your blood, it has less energy available to actually move your body in the direction you are trying to go.
• Prevents thermoregulation – As blood and fluid volume in the body decreases, your body does its best to prevent this loss.  To do this, the body inhibits the pathways that vasodilate (vasodilation: the widening of blood vessels) your blood vessels preventing easy flow of blood to the skin. This is a problem because blood traveling to the skin is one mechanism for keeping your body cool (the other being sweating). When blood is not able to be moved to the skin, heat is retained in the body. The hotter you get, the more your body has to work to keep your body cool rather than propel you forward.
• Heart rate increases – During prolonged exercise at a constant effort heart rate increases.  This phenomenon is called cardiac drift and is influenced by many factors.  How hydration alters it is through the decrease in blood volume.  The heart is forced to work harder to pump a smaller volume of blood through the body. To compensate, heart rate increases and the results in fatigue to set in earlier.  You get a double whammy here because cardiac output (the amount of blood pumped over a given time period), decreases for another reason as well. As your heart beats faster, it has less time for each chamber to fill with blood. This effectively limits your performance as your body cannot receive as many nutrients it needs in order to train or race harder.

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Weigh without clothes before your next higher intensity training session that is around 60 minutes in length. Make a note of what the training conditions are like so you have that as a future reference point. Heat index and overall level of intensity are the two most important.

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Go knock out your training session. While you do so, make sure you are logging the amount of fluids (if any) that you consume. Depending on your training conditions, you may not even need to hydrate for this 60 min or so session.

This session can be indoors our outdoors, but again, the external factors are important to record since your sweat rate will change based off it.

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Weigh yourself post workout, again in the birthday suit. You do not want your clothing, especially sweat filled clothing, affecting the results.

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Punch in the required fields below, and then adjust the amount of fluids you are consuming per hour to stay under 2% fluid loss. If your sweat rate is extremely high and you physically can't take in that amount of fluid, try to keep it under 3% and then test it on longer workouts. You may also consider preloading 2-3 hours before a long ride with 32oz of fluid and a larger concentration of electrolytes.

Note: This is ONLY for fluid replacement. Do not forget to replace electrolytes that are lost in that fluid. Electrolyte needs are not as easily tested, but if you would like to get a Precision Hydration Sweat Sodium Concentration Test done, just give us a shout.

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Now some of us that are looking to shed a few LB's may love the sight of seeing 3 pounds lighter on the scale, but this isn't the "good" weight loss.

If you've seen you are 32 ounces lighter at the end of a training session or race, take the next few hours post training and replenish those fluids. This doesn't mean you have to chug a huge 32 oz bottle, but make sure you're conscious about getting in that 32 oz of fluids you lost. We call this "topping off" your fluid levels.

You also need to make sure you are replacing electrolytes either through sports drink, or naturally sodium rich foods (many fruits and veggies).

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Before your next training session, take a second and compare your upcoming workout and training conditions to your what they were when you calculated your sweat rate.

Is it going to be a similar intensity level but the temperature (and more importantly, heat index) is HOTTER? Well, you better add a few ounces to your planned fluid consumption every hour.

Are you going to be training just as hard but for a much longer duration? You may want to pack extra bottles or have a route planned out that will allow you to refill if necessary. If you're racing, find out about whether there is going to be neutral support, or better yet, try and have someone working the feed zone for you.

Do not be surprised if you need to drink A LOT MORE than you previously have been. It's not uncommon to read stories about pro athletes going through 12+ bottles during a race. I once drank 8 bottles on a 3 hour training ride with the heat index at 115 degrees Fahrenheit and came home 6 pounds lighter than when I left. That's a lot of fluid loss. And yes, I felt HORRIBLE by the time I got home.

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Re-calculate your sweat rate on a regular basis. As with anything, the more points of data you have the better off you are going to be at dialing in your hydration needs and how they change based on intensity and external factors like temperature, humidity, and wind, among others.

Once you get used to it, it only takes few minutes at most and it provides some very valuable information with you to help not only maximize your performance during your training, but also your recovery once your training or racing has ended.

Eventually, you'll get to the point where you don't even need to think about it and it will just become habit.

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