Hydration: How to calculate how much you need during training and competitions

Your hydration status doesn’t have to be complicated.

Hydration is something that I take very seriously. I was a collegiate track athlete. Don’t look me up, it won’t be impressive or worth your time. And why is that? Because I was injured All. The. Time. Every time that I began to get quicker, jump higher or start to surpass teammates, I would inevitably become injured. I see now that it was due in part to my lack of nutrition and recovery plan, not adjusting the training for my individual body, and the big kicker: HYDRATION.

Specifically, one season when I was finally beginning to kill it, we were doing sprints with spikes on and I strained my hamstring. I was out for a couple of weeks and fell off of the Conference roster. I was devastated but had only myself to blame. I had almost nothing to drink that day. I had a full day of clinical hours at the hospital and did not have time to drink any water. Let me rephrase that. I did not MAKE TIME to drink any water. Unless you struggle with clean water availability, it is your duty to your body to make the time and effort to become hydrated. No excuses.

The issue with this story is that it is on the extreme end of what exercising or living in a dehydrated state can do to you. Being dehydrated is just as detrimental without the severe injuries, however is almost more dangerous because it can go undetected, flying under your radar. If you are looking to gain peak performance, not dying in the backcountry, weight loss, or improved body function, proper hydration is a non-negotiable factor.

Some things that are important to note prior to jumping in. Your individual sweat rate is dependent on fitness, acclimatization, gender, age, temperature/humidity and even genetics. So with that in mind, as you make strides toward your fitness goals, you may have to replenish less during activity, so make sure to re-evaluate throughout your season and from season to season.

Benefits of hydration

  • Being hydrated delays fatigue and perceived exertion. Do I even need to go on?
  • When you are dehydrated your mental acuity decreases and you tend toward poor performance
  • Hydration aids the body’s ability to cool itself during exercise
  • Reduces likelihood of cramping
  • Reduces overheating and illness
  • Being hydrated aids in necessary body functions. For example, water in blood transports glucose, oxygen, and fats to working muscles (super important) and removes lactic acid, carbon dioxide, and other metabolic by-products
  • Water throughout the body lubricates joints and provides cushion for your organs
  • Being hydrated decreases the viscosity of blood (meaning it makes it less thick and more fluid) –> which increases blood flow –> causing an increase in oxygenation to your muscles –> leading to improved performance, lower perceived exertion, decreases soreness.

I have shown athletes before the difference between honey and water pouring. If you are hydrated you are making your blood look more like water. If you are dehydrated, you have what we called “honey blood.” How do you think you are performing well if you have honey sludging through your veins trying to get oxygen to your poor muscles?! #nohoneyblood

*If you feel chronically fatigued, have a headache or are lethargic you may be chronically dehydrated

How much is enough?

First of all, start each training period well-hydrated. Many people begin their training dehydrated from their previous training session or just not drinking any fluid during the work day. It is sometimes difficult to replenish during activity and even more difficult to replenish while also trying to counteract a deficit.

During activity, your body copes with the increasing temperatures and exertion by sweating, causing you to lose fluid and electrolytes. One of my favorite ways to determine how much to replenish is by utilizing a sweat rate loss test. It is simple, it only takes five minutes to calculate, and the best part is that it is FREE.

Here are the easy steps to determine how much you need during activity:

1. Weigh yourself prior to working out. It is preferable that you do this nude, but let’s not do this if we are at the gym, okay? The key is be consistent before and after with amount of clothing.

2. Work out for one hour. During this time, it is crucial you count how many fluid ounces you consume, and you cannot go to the bathroom. I like to use a water bottle that has ounce markings or if I know how many ounces it contains, consume its full contents for easy math. For triathlons, I will do this on the bike for one hour or run for an hour. I also recommend doing this for strength training and swimming as well; this knowledge will help you stay hydrated during training.

3. Weigh yourself afterward. Calculate the difference and add in the ounces from your fluid.

*It is important to note that one liter of water (~32oz) is equal to 2 pounds.

Example: 150.2 lbs pre-workout – 148.2 lbs post workout = 2.0 lbs loss

Convert pounds to ounces by multiplying by 16 oz: 2.0 lbs x 16 oz = 32 oz

Add fluid consumed during activity: 32oz + 12 ounces consumed = 44 ounce fluid loss during activity (or 1.3 liters)

4. This calculation gives you your sweat rate loss for one hour.

With this number you can use this to determine how much you should drink per hour during the same or similar activities, adding or subtracting based on intensity or weather conditions. If you are planning on running a 50-miler in 13 hours or trying to determine your consumption for a 5.5 hour Ironman bike leg, simply just multiply that loss per hour by how many hours you anticipate you will be doing the activity.

It is sometimes difficult to consume that much water during your workouts though. You don’t want your stomach to be sloshing around while you are trying to run. But you have to train your body in drinking fluid during activity just like anything else in training! The major take-away is that you should never lose 2% or greater of your body weight during activity. This is very critical in any sport and any activity. At this point you start making slower decisions, your body functions begin to slow down, and you can begin to have dehydration symptoms. Now, you are not going to weigh yourself every day, I actually do not recommend that. So, you only need to do this once or a few times and use the calculated number to help you out later when planning. When calculating how much fluid you need to bring on a long cycle you should calculate how much your optimal fluid per hour intake is and bring along for the ride 80%-100% of that. For long runs I HIGHLY suggest hydration packs, handheld bottles, setting up hydration points or having a friend ride a bike beside you. Remember, it is also important to rehydrate afterward as well.

*Tip: Test how many ounces you consume in a gulp. This is helpful for the run in particular in races when you are not carrying your bottles but using aid stations.

While the sweat rate loss test is simple and quick, there are a lot of less fancy ways to determine hydration status. How often are you urinating? (Every 1-3 hours.) Does your urine look more like lemonade or apple juice? (It should always look like lemonade!) For your body to feel the best that it can and to perform at its highest level, whether you are doing an Ragnar race or a really hard math problem, you NEED to be hydrated. The question that always arises is, “but if I am carrying my water, it is heavy and it slows me down.” I understand that and have the same argument with myself. However, when you are properly hydrated, your perceived exertion decreases. Your muscles receive more oxygen. You do not have to suffer through dehydration symptoms. And you are less sore the next day. (Also, quit whining and view it as resistance training!) I implore you to go back and read all of the benefits listed with hydration. Additionally, if you do not train now to drink that much, your gut will not take kindly to that sloshing on race day!

We are past the foolish days where coaches think water breaks are for those who are weak. Try hydrating my way and uncomplicate your relationship with your hydration status.

Always remember to replace early and often!!


Bonus: If you are training pretty hard for whatever activity you are building up for, check out the commonly accepted activity-based hydration recommendations below!

5-7ml/kilogram body weight, 4 hours prior to exercise (1 kilogram = 2.2 pounds)

14-22oz, 2 hours prior

8oz, 10-15 minutes prior

6-8oz of H20 or sports drink every 15-20 minutes during exercise as tolerated.

Post-activity: 16-24oz per pound body weight lost during activity (weigh before after) within 2 hours post workout.

+hydrating before, after, throughout day.

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