Dehydration: the simple mistake hurting your training. Part 1 in a series on the importance of the body's fluid balance.

Thirst is our bodies’ signal that we need more fluid.  But sometimes there’s a “lag” in this signal – dehydration may happen before we become thirsty.  Or we miss these thirst cues because we aren’t aware of them.  

I made this mistake due to years of conditioning myself to “not need water breaks” when I played college soccer because I thought it made me look tough.   After college, during my early years as a runner, I thought I was young and resilient enough (in actuality…stupid) to not need as much water as everyone else.  I didn’t feel thirsty-  why would I need to drink?  

If I ran through the water stations, maybe I could pass a few extra people who were stopping?!   Not a great thought process…

One year, our cold Cleveland spring quickly turned into summer.  A rapid change from a 40 degree month of April into an 80 degree first week of May left me wondering why my workouts suddenly felt harder than normal and why the Cleveland Half Marathon was one of my worst races in memory.  I PR-ed a 10 mile race a few weeks earlier (in the cold) and was expecting to do that same with my 13.   

I chalked my disappointing performance up to a crazy work schedule, bridesmaid duties at a cousin’s wedding, and not tapering my weight training properly.   But my poor workouts continued for another month and I started getting headaches, craving salty foods, and being horribly tired (and cranky).  I knew something was wrong.  

After researching probiotics, adrenal fatigue, and a million other things that were more complicated than drinking more water, I finally wised up and decided to calculate my hydration needs per day.  

I was drinking only half as much as I should have been.   I was clearly dehydrated and this had compounded for over 2 months.  As soon as I drank what my body needed, I felt better with more energy.  My workouts weren’t as miserable and I was back to my normal performance.

I’m not the only one with poor ability to notice my dehydration.  In 2016, this study from the International Journal of Sports Nutrition and Exercise Metabolism found that 32% college athletes started training in a dehydrated state and almost 44% finished in one.

It’s also common for people to rely on processed and nutrient-poor drinks.   We get mixed messages from the beverage industry about what is healthy and what isn’t.  Does anyone remember Coke’s marketing campaign from a few years ago that said “all beverages are hydrating?”  Talk about misleading…

These drinks can mute our thirst indicators.  Some contain caffeine, which can further dehydrate us, and the extra sugar or other chemicals can interfere with other body functions.  

So why is water important?

Water makes up over half of who we are-  55-60% to be exact.  

Why do we need it?

  • Water helps regulate our body temperature.  When we get too hot, we sweat.  The evaporation cools us down. 
  • Water also…
    • Carries nutrients to cells and takes waste products away
    • Allows most chemical reactions in the body to happen (water is a “catalyst” for them)
    • Lubricates joints; acts as a shock absorber for the eyes and spinal cord 

We basically need water for every bodily function, which is why dehydration is so dangerous   

I mentioned before that sometimes there is a ‘lag” between losing fluid and being thirsty.   As a result, we may notice something is off with how we are thinking, focusing, or performing before we realize we’re dehydrated.  

Our thirst signals may not kick in until we’ve lost 1-2% of our body fluid.   

Other signs of dehydration include:

  • headache 
  • fatigue
  • low blood pressure
  • dizziness, fainting
  • nausea
  • rapid heart rate

Loss of body fluid gets dangerous quickly:  

0.5% loss =  increased strain on the heart. 

4% loss =  decreased muscle strength, heat cramps

6% =  physical exhaustion, heat stroke, coma

10% or more = death

How much water do we need?

Everyone’s hydration needs are different. Most adults need 3L (12 cups) of fluid each day, but this goes up or down with certain factors:

  • Types of food eaten on a given day: 
    • Raw fruits and vegetables = high water content 
    • High-fat foods (nuts, seeds, oil, butter) = low water content
  • Body size:  bigger people need more fluid 
  • Climate and temperature
    • Warmer weather- may need an extra 500 ml (2 cups)
    • Drier air – may need up to 6L (24 cups) per day
  • Alcohol consumption
  • Excessive caffeine consumption
    • 1 cup of coffee is probably ok per the National Athletic Trainers Association – read more here.
  • Stomach or digestive issues; diarrhea, vomiting, sickness

Estimating your own individual needs:

  1. Divide your body weight in pounds by 2.2 to determine how many kilograms you weigh. 
  2. Take your weight in kilograms and multiply by 30-40 to determine how many milliliters of water needed per day.
  3. Convert milliliters to cups, ounces, or whatever is easiest for you-  and drink up!

A 110lb person would need between  6-8.4 cups per day (1.5-2L)

A 220lb person would need 12.5-17 cups (3-4L)

For exercise:  we generally sweat out .5-2.0 L per hour of activity.  Make sure to replace that as well.  

Hydration done right:

  • For light to moderate exercise 
    • Drink .5-1 liters (2-4 cups) of water during activity and another 2-4 cups after workouts.  
    • Make sure to drink 1-2 cups of water at each meal.  
      • Doing this alone would account for 3-6 cups of water per day!
  • For elite athletes – calculate hydration needs based on body weight as above.  Also consider sports drinks or recovery drinks to replenish carbohydrates, electrolytes, and protein.  Stay tuned for Part 2. 
  • Drink 1 cup of water for each cup of caffeinated or alcoholic beverages you consume. 
  • Increase your water intake for longer workouts, warmer weather, or drier weather. 
  • Carry a water bottle with you and fill it up twice a day.  (This, along with a drink journal are my “go-to” strategies.)
  • Keep a “drink journal”  to track cups of water, alcohol, sugar-sweetened beverages, etc for 2 weeks.  You can track it in the “notes” section on your phone, a calendar, note pad, or whatever is easier.  After 2 weeks, review it and see what changes need to be made –  increasing water intake?  Scaling back on sugary drinks or alcohol?  Set a goal to change one thing over the next two weeks   


Drink regularly, especially if you are an athlete.  

Some athletes need more than just water.  Stay tuned for Part 2 where we look at electrolytes, proteins, and carbohydrate based sports drinks and who can benefit from them. 

CLE Sports PT understands that hydration needs vary for each person, activity, and training cycle.  Schedule a nutrition consult to determine your own needs and get a realistic plan to hydrate properly on YOUR schedule.  Or try a 15 minute free consult to get your hydration questions answered.  


  1. Berardi, John et al. The Essentials of Sport and Exercise Nutrition. Precision Nutrition, Inc, 2017.
  2. Magee PJ, Gallagher AM, McCormack JM. High Prevalence of Dehydration and Inadequate Nutritional Knowledge Among University and Club Level Athletes. Int J Sport Nutr Exerc Metab. 2017 Apr;27(2):158-168. doi: 10.1123/ijsnem.2016-0053. Epub 2016 Oct 6.
  3. McDermott BP1, Anderson SA2, Armstrong LE3, Casa DJ3, Cheuvront SN4, Cooper L5, Kenney WL6, O’Connor FG7, Roberts WO8.  National Athletic Trainers’ Association Position Statement: Fluid Replacement for the Physically Active.  J Athl Train. 2017 Sep;52(9):877-895. doi: 10.4085/1062-6050-52.9.02. (