Dehydration is the main cause of DNF’s 😮

Okay that’s not entirely true it’s put down to Nausea and/or vomiting 2nd to that unable to make cut-offs. But read on and you will see how hydration is key to everything.

To physically complete the distance is not a limiting factor for success. With structured training and smart planning, you can overcome the challenges of any ultramarathon.

But it all comes undone when your nutrition and hydration strategies fail. 

When it comes to sports nutrition for ultras, fluids are even more important than calories. During exercise, macronutrients have one essential job: to provide energy to working muscles whereas water in contrast plays a wide variety of roles and each is critical to success.

Regulating your core temperature is water’s most obvious role during exercise. The body likes to operate in a narrow temperature range and optimally at 36 to 37 degrees.

Consequently, a lot of the heat generated from exercise must be dissipated to maintain optimal core temperature.

Sweat is our primary cooling mechanism. As core temp rises your sweat glands kick in and push it to the surface of your skin. That fluid then gets replaced by fluid from your blood plasma. Making your blood volume a major reservoir of potential sweat.

The amount of fluid you need depends on sweat rate and body size and varies greatly with intensity, temperature, wind and humidity.

GUT MOTILITY AND DIGESTION

Without enough fluid your body can’t break down and absorb food effectively. This means your nutrition strategy is dependent on your hydration status.

Without adequate hydration, you can’t get the carbohydrates from the intestines into the blood. If you don’t the food sits there until enough water is available. Either by drinking enough or it’s pulled from your body into your intestines.

When you are exercising and pumping a lot of sweat onto your skin to cool off the body will prioritise thermal regulation over digestion and digestion slows dramatically.

This is often the tipping point for GI Distress because once it drops it can take a long time to return to normal. The food that sits there starts to ferment and is jostled about, leading to pressure and bloating and all the GI Issues you don’t want.

BLOOD VOLUME

You have about 4.5 to 5.5 L of blood in your body, and it never stops moving. We always focus on blood's role in delivering oxygen to working muscles, but blood also delivers the nutrients your cells need to function and takes away the waste they produce. Blood also carries heat away from the core to the extremities and skin in order to maintain a healthy body temperature.

Finally, blood plasma provides the fluid that ends up being excreted as sweat. One of the key responses to training and acclimation to heat and/or altitude is an increase in blood plasma volume. It's your body's way of filling the reservoir to be prepared for the anticipated activity and environment.

When you run low on fluids and plasma volume drops, your body starts prioritizing how to use what's left. In cold temperatures or at high elevation, athletes with a better hydration status stay warmer longer. Dehydration hastens the onset of hypothermia. When it's hot outside and your plasma volume gets a little low, you’re resting and exercise heart rates increase. Your heart must pump faster to deliver the same amount of oxygen using less fluid. When plasma volume gets even lower, your body prioritizes sweating over digestion, and if the situation gets dire, it prioritises oxygen delivery over sweating, and you end up with heatstroke.

WASTE REMOVAL

Removal of metabolic waste products is another crucial role for fluids. This is of particular importance to ultrarunners because of the amount of muscle damage sustained during 50- and 100-mile events. The kidneys filter waste products out of your blood and excrete them in urine. With mild dehydration, urine production diminishes, and the colour of your urine starts to darken. More severe dehydration can damage your kidneys and alter the pH of your blood.