Slaying the 3-headed Monster: Weight cut, fatigue and dehydration.

In my last post I addressed the challenge of keeping key metabolic hormones in check during your weight-cutting period.  This blog segment focuses on taking down your hidden competitor: Fatigue. And more specifically, how dehydration empowers fatigue, pushing much of the progress and improvement you’ve trained for completely out of reach.

Sport scientists define fatigue as a decrement in the force output of a muscle.  Psychologists see fatigue as a ‘sensation’ of tiredness.  And physiologists define fatigue as the failure of a specific physiological system. Consider that exercise is terminated at exhaustion—and not at a point of fatigue.  It is widely accepted that fatigue is a safety mechanism that has evolved to prevent injury or death by means of overreaching.  But regardless of how you define it, fatigue is something we all fight with; and regardless of physical and mental preparation, fatigue will always be present.

What causes fatigue?

There are many things that can cause fatigue, not the least of which is 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 to, 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 rates.

Researchers have identified fatigue mechanisms that originate in the neuromuscular system.  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%.  Researchers are not clear on all of 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 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 suggests that sweeter isn’t necessarily better.  In fact, scientists have shown that just sensation of sweetness in the mouth—not glucose itself—will dampen the fatigue effect.  In various studies, athletes were asked to “swish the fluid around in the mouth, then spit it out.” Those athletes saw an increase in performance versus those who merely drank water.  Other studies using sugar have also shown that more is not really “more.” 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; 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.

Our brains monitor hydration levels closely.  Because the brain interprets dehydration as stress, it triggers a drop in performance.  Too much dehydration triggers production of stress hormones.  The brain will limit the number of muscle fibers you can recruit.  Remember, a drop in total body water causes a drop in blood plasma volume, which limits the body’s ability to deliver nutrients to the muscles.   We see this in combat sports like boxing and wrestling and it’s been documented in sports as diverse as triathlons.  Many times hydration is a consideration of safety.   Dehydration can lead to cramping, exhaustion and even death due to heat stroke.  But long before we get to the point of illness, dehydration is contributing to fatigue and limiting performance.  The takeaway: Be sure to harvest all the hard work you’ve done leading up to your event by keeping the opponent of fatigue on the bench.  Stay hydrated!