Dehydration can cause up to a 5-7% decrease in power/performance. That’s huge! A 5-7% decrease in performance could mean the difference between winning a race and finishing well out of the top 5.
What does it cause the body to do?
I’m going to get a little scientific here so bare with me. One of the best explanations for this decrease in performance due to dehydration is a scientific term called cardiac drift. It’s a good place to start and for this article will be the main place I focus.
Cardiac drift refers to your heart rate slowly increasing while your power/effort/pace essentially stays the same. Typically this is best seen over a long workout, but for less experienced athletes can occur even earlier.
What’s exactly happening?
Well your heart is having to work harder and harder at the same work rate. That’s not a good thing. Ideally, you want you heart rate to stay the same while your power/pace/effort stays the same. That means it is meeting the demands you body is requiring. So why is it going up?
Reason being is fatigue, and a very large part of this is dehydration. Why? Because your blood is made of a ton of water: less water due to dehydration means your blood is thicker, and there is also less of it altogether. For you scientific guru’s basically your Stroke Volume, of SV, is decreased significantly or in more basic terms you have less blood to pump. Less overall blood to pump means your heart has to pump harder to get the same amount of oxygen and nutrients to your working muscles. That’s not a good thing at all. Less blood, less oxygen to your muscles, and a higher heart rate means a definite decrease in performance.
Here’s a graph(see attachment/photo at top page) of an athlete I coach that did a 4 hour steady state ride in Florida. Power is in yellow on the bottom and HR is in red at the top. This might explain it a bit better for the visual learners out there: you will notice in the graph that there is a very precise moment about 3 hours in where power stays the same, yet heart rate continues to rise. This is not a good outcome, and will result in faster fatigue and overall sub-optimal performance.
So what’s the solution? How do you fight this issue when training and racing?
The two quickest and easiest tasks you can do during your next workout or race are great hydration and trying to keep the body as cool as possible.
Hydration: simple, take in a minimum of one 24-32 ounce bottle of liquids per hour, minimal! For most riders in more humid/hot climates, I recommend trying to take in closer to two of these per hour. Sounds like a lot, but as long as you aren’t causing any gastric distress, then you are only doing your body/heart good. If you can’t finish both bottles, then use the extra water to pour slowly over your head. This can aid in reducing the increase in your core body temperature which can be pleasing mentally, and also improve your physical performance.
Keep in mind the challenges you run into while working out/racing: i.e. where am I going to refuel, how am I going to get bottles(in a road race for example), and how many bottles will I need to finish my workout today. Plan, plan, plan! That’s a huge part to succeeding in endurance events.
Few other things to keep in mind:
1) Your body absorbs cool water better than warm water. In the very hot/humid summer heat for example down in Florida, I highly recommend looking into some of the Polar Bottles. Those will keep your liquids cooler for a much longer period of time. Throw a few ice cubes in your bottles and you will be set to go! Otherwise, just make sure you are chilling your fluids for longer rides.
2) Everyone is a little different when it comes to hydration needs. Women tend to be more efficient and sweat less, meaning they need less water. Also, the lighter you are, the better you will deal with the heat, whereas heavier athletes tend to have more issues. The key is knowing how much you sweat and making sure you are replacing as much as you can while riding.
If you are concerned about this, weigh yourself before and after your workout. For every 1 lb you lost during your ride, make sure you drink a bottle of water. Ideally, you want to minimize this weight loss as much as possible. Less water loss means you are hydrating better.
3) Hydration not only affects your performance in your workout today, but also will affect how you perform tomorrow. If you become dehydrating one day, there is more likelihood you will be behind and somewhat dehydrated tomorrow also. So make sure you replace your water needs as mentioned above.
That’s the general run down. Follow those steps and you will be on your way to performing better and for longer periods of time practically overnight.
Coach Drew Edsall: Professional Mountain biker, Head Coach and Founder of Mtbfitness
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