The Three Headed Monster of Weight Cut, Fatigue and Dehydration


By: Don Moxley, M.A.  Exercise Physiologist, Hydrus Sport Science Director

I wrote about the challenge of keeping key metabolic hormones in check during your weight cutting period in my last post. In this segment I want to take some time to discuss your hidden competitor, fatigue, and how being dehydrated empowers fatigue and locks much of the progress and improvement you’ve trained for out of your reach.

Sport scientists define fatigue as a decrement in the force output of a muscle. Psychologists see fatigue as a ‘sensation’ of tiredness.  Physiologists define fatigue as the failure of a specific physiological system. Exercise is terminated at exhaustion, and not at a point of fatigue. Many consider fatigue to be a safety mechanism evolved to prevent injury or death from over reaching. However, regardless of how you define it, fatigue is something we all fight with, and regardless of the preparation, fatigue will always be present.

What causes fatigue?

There are several factors that can cause fatigue, not the least of which is just engaging in a work event that is beyond your capacity. This type of fatigue is caused by our body’s inability to deliver the necessary oxygen or nutrients in the blood to the working muscles. This is why we train, to increase that capacity. But even if we have trained and have the ability to do the necessary work, other factors can creep in and block our ability to accomplish our goals.  Hydration levels have a direct impact on the blood volume and contribute to success and failure.

Researchers have identified fatigue mechanisms that originate in the neuromuscular system as well. These seem to be protective systems in the body that can originate as high as the brain in the central nervous system. Research has shown that in some athletes this level of fatigue can limit work output by up to 32 percent. Researchers are not clear on all the factors that contribute to this “central governor” fatigue model, but some that have been clearly shown are an imbalance in electrolyte concentrations, and the brain’s perception of a lack of fuel. The ability to replace key electrolytes and in-turn draw water into the blood plasma is an important part of strategic rehydration.  

Research has also shown that sweeter isn't better. In fact, scientists have shown that just the sensation of sweetness in the mouth will dampen the fatigue effect. In studies, athletes were asked to just “swish the fluid around in the mouth, then spit it out”. Those athletes saw an increase in performance against those who just drank water. Other studies using sugar have also been clear; more is not better. Athletes consuming concentrations as low as 2% have had similar exercise times to failure as those consuming 18% concentrations.  In another interesting study, athletes were given glucose through an IV and those athletes saw no improvement in performance over water alone.  This is an area that needs more research, but for now, be confident that a little sweetness goes a long way.

The brain monitors hydration levels closely, and if it senses dehydration, interpreted by the brain as stress, it will trigger a drop in performance. Too much dehydration alerts the brain to release stress hormones. The brain will limit the number of muscle fibers you can recruit. Remember, a drop in total body water will cause in a drop in blood plasma volume and will cause a drop in your body’s ability to deliver nutrients to your muscles. We see this in combat sports like boxing and wrestling and it’s been documented in sports as diverse as triathalon. Many times, hydration is a consideration of safety. Dehydration can lead to cramping, exhaustion, and even death in some cases from heat stroke. However, long before we get to the point of illness, dehydration is contributing to fatigue and limiting your performance.  Be sure to harvest all the hard work you’ve done leading up to your event by leaving fatigue on the bench; Stay hydrated!


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