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How Hydration Impacts Blood Volume (and Why That Matters)

When we exercise we naturally get dehydrated while, at the same time, we have to deal with a rising core temperature due to the heat created by work performed. The key to these issues is really our blood and blood volume. During exercise, blood plays a few key roles in assisting performance, including:

  1. Helping the skin to dissipate heat;
  2. Delivering oxygen and other nutrients to the muscles and carrying waste products away;
  3. Circulating through the abdomen to help absorption of calories

We only have so much blood in our body, somewhere between 5 and 6 liters for most of us, and this creates a competition between skin, muscle and the abdomen for the blood that constantly circulates in our body. We can chop the abdomen out of the equation quickly, as nutrient absorption will always lose out to the skin and muscle requirement. The real battle occurs between skin and muscle. As you exercise more and more you will become dehydrated and your blood volume will begin to drop (as the blood has plenty of 'water' in it). As blood volume drops the battle intensifies, as there is less blood available to keep our systems cool, as well as deliver the nutrients and oxygen required to maintain the work desired. The inevitable winner in this battle is the skin, as rising core temperature has real potential health consequences, and as a result you begin to feel an onset of great fatigue as an athlete. This explanation should begin to lead you into the value of proper hydration. We can summarize the value of hydration as:

  1. Maintain and retain blood volume to prevent early onset of fatigue and maximize cooling opportunity.
  2. Assist in the transport of calories taken in to fuel performance.
  3. Assist in recovery from workouts but preventing highly stressful dehydrated state.

So where should you start? I like to tell athletes to think of hydration as an 'IV' of fluids; in other words, very frequent and consistent ingestion of fluids, versus big gulps every 30 to 40 minutes. Drip-feed your hydration... your stomach and blood will thank you.

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