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Individualizing Your Hydration Plan

This is an excerpt from Nutrient Timing by Lauren Link.

Beyond the general recommendations, you may need to individualize your hydration plan a bit further. If your urine is consistently light in color and you do not have any specific problems with staying hydrated there is no reason for you to test more specifically. However, if you are experiencing symptoms of dehydration (cramping, fatigue, headaches, etc.) and feel that you could benefit from knowing more details about your hydration needs you might consider some of the following tests.

Weighing In and Out

Weighing yourself before and immediately after a workout is one of the simplest ways to assess fluid loss. It is a common misconception by athletes that weight loss during a workout is true weight from fat. The practice of wearing sweats to try to promote sweating to “get weight down” is an old-school favorite that unfortunately is doing nothing besides causing dehydration. It is well documented that even during longer workouts of two to four hours, any weight that is lost is not coming from fat or muscle mass, but instead from fluid. Small amounts of fat and muscle loss have been seen during ultraendurance training of six to eight hours or more (Knechtle, Rosemann, and Nikolaidis 2018), but most athletes should assume that any weight loss during a workout is simply from fluid.

With this in mind, measuring your pre- and postworkout weight will help you easily quantify fluid loss. It’s important to take both weights wearing the same clothes and shoes so as not to skew the results based on equipment. If you are a swimmer, you should shower prior to the initial weigh-in so that you simulate similar conditions that will be present when you get out of the pool afterward.

As mentioned previously, it is recommended to drink 2 to 3 cups (16-24 fl oz) of fluid per pound lost. Once you have determined how many pounds you lost, you should aim to replace that fluid over the next four to six hours. Therefore, an athlete who lost 5 pounds during a workout or competition should aim to drink 10 to 15 cups of fluid over the four to six hours following the conclusion of that workout. In the case of extreme fluid loss this time frame may not be realistic, but you will want to ensure that you have replaced that fluid before your next workout. Although replacing lost fluids is paramount, if you are consistently losing a fair amount of weight during training you should also focus on consuming more fluids throughout training to minimize these losses.

For most athletes, the simple practice of weighing in and weighing out a couple of times is more than enough to help guide hydration without creating too much of a focus on body weight. Getting a general feel for how much weight you tend to lose during certain types of training will give you a good goal to aim for in terms of rehydrating. However, as mentioned throughout this book, if you have struggled with body image or if weighing yourself causes you stress and anxiety, this practice is probably not in your best interest. You would likely be better off monitoring your urine color, and as long as you are not a very heavy sweater and not having problems staying hydrated, this should be adequate.

Sweat Rate Testing

Sweat rate testing builds off this weighing in and out practice to calculate your individual sweat rate, or the amount of fluid you lose per hour via sweat. This is more involved and requires a fair amount of control of your environment immediately around the workout. In addition to weighing in and out, you also need to track any fluids in and out of your body. This includes total ounces consumed from your water bottle, as well as volume of urine output, if applicable. There are great sweat rate calculators online—a quick search should yield many options that allow you to hone in on this aspect of your performance.

Sweat Testing

Objectively evaluating hydration status via formal sweat testing involves not only measuring sweat rate, as outlined previously, but also includes wearing patches to collect sweat so that you can quantify the amount of electrolytes (specifically sodium) that are being lost. Although sweat testing has historically been limited to high-level athletes working with practitioners who have access to labs, accessibility has increased substantially in recent years with the development of sweat patches that can be used even by the layperson. Purchased online or through local sporting goods stores, these patches are worn during a training session or competition and used in conjunction with an app to measure sweat rate and the amount of electrolytes lost. If you do use one of these sweat tests, I would encourage you to try to do them in a controlled environment for the best possible results and to pay close attention to those results. Most of these tests will not only tell you your individual sweat information, but also suggest changes you could make to improve your hydration habits based on those results.

As a reminder, all of these methods for assessing your hydration status can be helpful, but none are necessary for the majority of athletes. If you are managing your hydration well (urine is generally light colored and you have no cramping, unusual levels of fatigue, lightheadedness, or overheating) then there is generally no need to delve further into these specifics. However, if you are struggling with hydration in any manner, one of these tests can help you better manage this aspect of your fueling.

More Excerpts From Nutrient Timing