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Hydration, sweat loss, and fluid needs

This is an excerpt from Dance Injuries With HKPropel Access by Jeffrey A. Russell.

By Ann F. Brown, PhD, CISSN, FIADMS; Meghan A. Brown, PhD, FHEA, SENR; Jasmine D. Challis, RD, MRes

Euhydration is the state in which the amount of water in the body is optimal; it is commonly called being hydrated. The body loses water constantly through breathing, skin perspiration, and urine production. Dehydration, the state in which body fluid levels are suboptimal, has negative short- and long-term side effects. Your body functions best at a core temperature of around 96.8 to 98.6 degrees Fahrenheit (36-37 °C). Many essential body processes do not work as well at temperatures above and below this range; at temperature extremes, dance is not possible.

All physical activities—including dance—result in heat production. Sweating is the main route for heat loss during physical activity in humans; the evaporation of sweat reduces the body’s temperature. Although sweat rates vary, approximate average values are 800 to 1,200 milliliters (mL) (27-41 fl oz) per hour for males and 400 to 600 mL (14-20 fl oz) per hour for females (Baker, 2017).

Rehydration

To cover the essential water requirements of the adult body, female dancers typically need at least 1,500 mL (50 fl oz) of fluid per day, and male dancers typically need about 2,500 mL (85 fl oz) per day. Additional fluid is required to replace sweat losses; research recommends 1.25 to 1.5 mL for every 1 mL lost (Academy of Nutrition and Dietetics et al., 2016). The benefits of fluids other than water are discussed later in this chapter. Aim to start any exercise—including dance—in a state of euhydration.

It is helpful to know you can tolerate longer periods—up to an hour during training—without taking fluids; however, during training, the main priority should be staying hydrated to reduce injury risk (Jones et al., 2008). Some foods—particularly vegetables, salads, and fruit—have a very high water content, so those who include large amounts of these foods in their diets may find their need for fluid is slightly less than it would be otherwise. Your body will use fluid most effectively if

1. you have done a suitable warm-up; it diverts blood from the kidneys and thus it reduces urine formation.
2. you take in fluid regularly when exercising for more than an hour (e.g., 150-300 mL [5-10 fl oz] about every 20 minutes).
3. you continue to drink fluids regularly to restore euhydration after exercise.

From a practical perspective, being aware of the volume and color of urine you produce is a good guide to hydration. Thirst can be a reliable guide to fluid requirement, but it is often not sensitive enough in physically active individuals with moderate to high sweat rates, especially for those dancers who find it hard to judge thirst. Lower urine volumes and darker color suggest dehydration. The method of measuring weight change (in dry clothing) from pre- to postexercise can help identify inadequate hydration. A rule of thumb is for every kilogram (2.2 lb) of body weight lost, replace it with 1.5 liters (50 fl oz) of fluid. Replacing this fluid is essential for recovery and for maintaining performance.

Sports Drinks

Sports drinks traditionally aim to be isotonic (having a composition similar to body fluids), in which typically it has a carbohydrate content between 4 and 8 grams per 100 mL (3.4 fl oz) plus electrolytes. Electrolytes are important minerals involved in the body’s fluid regulation and are often lost in sweat. Sodium, potassium, and chloride are found in virtually all sports drinks; however, some drinks may also contain calcium, phosphate, or magnesium. These liquids are designed to be absorbed readily, replace losses, and provide a small amount of energy for ongoing activity. See the Homemade Sports Drinks sidebar.

Many additional options are labeled as sports drinks; some of them supply only electrolytes, or perhaps they include a very small amount of carbohydrate. These types of drinks are hypotonic, which means they are less concentrated than body fluids. Water is hypotonic, and it is adequate for low-intensity dance classes. While research suggests that isotonic drinks can improve sports performance compared with plain water (Coso et al., 2008), evidence on hypotonic drinks is more limited. You should try different drinks, keep notes on their palatability and any unpleasant gut side effects, and opt for the one (or more) that works best for you. Always check the list of ingredients; you may prefer to avoid some of the additives, which can include artificial colorings, flavorings, sweeteners, and—in the United States—high-fructose corn syrup (HFCS). HFCS can raise blood glucose levels very rapidly. For dancers working intensively, this rise will likely not cause any problems because carbohydrate use is rapid. However, caution is advised under other circumstances. You should always have some water with you both as a drink and as a mouth rinse (to minimize adverse dental effects) after consuming carbohydrate-containing drinks.

For rapid hydration, avoid hypertonic drinks. These drinks usually have a sugar content of over 8 grams of carbohydrate per 100 mL (3.4 fl oz). They include fruit juices, smoothies, most fizzy drinks (sodas), and milk-based drinks. Cordials and other concentrated drink syrups should be diluted to a suitable level. Moreover, sports drinks can be diluted with water, too, as some border on hypertonicity.

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Homemade Sports Drinks

Generally, sports drinks tend to be isotonic (they have a mixture of electrolytes with a concentration similar to that found in your body), and they aim to replace fluid and electrolytes lost in sweat (including sodium, which is found in salt) as well as some carbohydrate (4-8 g per 100 mL [3.4 fl oz] of liquid). While there are many sports drinks on the market, they are easy to make at home. Following are a few sample recipes for you to try. Note that the lower amount of salt is adequate in most situations; however, use the higher amount of salt if you are dancing or training in conditions where you sweat heavily. Shake each of these drinks well after combining the ingredients.

1. Mix 400 to 600 mL (14-20 fl oz) of your preferred fruit juice with enough water to make 1000 mL (34 fl oz) of liquid. Add 0.5 - 1 level teaspoon (tsp) of salt.
2. Mix 1000 mL (34 fl oz) of water with 50 g (4 tbsp) of glucose and 0.5-1 level tsp of salt.
3. Mix 750 mL (25 fl oz) of coconut water with 250 mL (8 fl oz) of pineapple juice and 0.5-1 level tsp of salt.
4. Mix 900 mL (30 fl oz) water, the juice of two lemons, and 2 tbsp of honey. For a flavor twist, you can add sliced ginger to the water for an hour and then remove it before adding the other ingredients.

Hypertonic beverages have concentrations of dissolved components that are higher than what is found in your body. These concentrations are useful to consider for recovery. During recovery, the aim is to rehydrate as well as to provide both carbohydrate and protein for restoring glycogen stores and to start the repair of the muscle fibers damaged during intense exercise, including dance.

A great example of a hypertonic drink is a 500 mL (17 fl oz) glass of milk with 1 to 2 percent fat content. Soy milk is the most comparable plant-based source. This also includes milk with any flavoring that contains some carbohydrate, such as chocolate milk. Syrups, powders, and fruits (including berries) can be added to create milkshakes or smoothies with additional nutrients.

More Excerpts From Dance Injuries With HKPropel Access

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