Athletes' hydration needs before, during and after exercise

Maintaining your hydration status is of utmost importance to both your overall health and athletic performance. In fact, studies have consistently confirmed the link between hydration status and athletic performance in activities ranging from submaximal exercise to maximal-intensity aerobic performance in both warm and hot environments. But how much should you drinking and when should you be drinking it?

We explore these questions in this post, adapted from High-Performance Nutrition for Masters Athletes.

Pre-Exercise Hydration

Since hypohydration (uncompensated loss of body water that is greater than expected normal daily fluctuation) is known to adversely affect performance outcomes, it is important to start each training session and competition in a state of euhydration (a normal state of body water content), which requires adequate food and water intake during the 8 to 12 hours prior to each session. Unfortunately, but not surprisingly, research demonstrates that many athletes begin exercise already dehydrated.

To ensure optimal hydration status at the start of each session and to promote voiding prior to the start of training or your completion, you should aim to drink 5 to 10 milliliters per kilogram of body weight (2-4 mL/lb) in the two to four hours prior (Thomas, Erdman, and Burke 2016). Another helpful tool is to monitor your urine color, frequency, and volume to assess your fluid status (Maughan and Shirreffs 2008). Urine should be pale yellow in color when you are well hydrated. Darker color (apple juice color) and low volume urine generally indicate dehydration and may require an additional 3 to 5 milliliters per kilogram of body weight (1-2 mL/lb) of fluid about two hours prior (ACSM et al. 2007). Keep in mind that urine color can be affected by B-complex vitamins—which turns it bright yellow or orange—as well as some foods, medications, and food dyes (Maughan and Shirreffs 2008). Remember that you are looking for overall clues to help you better understand your fluid needs and status, and for changes from your normal. See the table below for guidelines on how to determine your specific pre-exercise hydration needs.

Pre-Exercise Fluid Intake Guidelines

Fluid needs	For 120 lb (54 kg) athlete	For 160 lb (73 kg) athlete	For 200 lb (91 kg) athlete
Drink 5-10 mL/kg (2-4 mL/lb) of body weight during the two to four hours prior to training or competition	256-341 mL (9-12 oz)	341-483 mL (12-17 oz)	426-597 mL (15-21 oz)
Drink an additional 3-5 mL/kg (1-2 mL/lb) of body weight about two hours prior if urine is still dark in color	142-256 mL (5-9 oz)	199-341 mL (7-12 oz)	256-426 mL (9-15 oz)

In an attempt to preload or hyperhydrate prior to exercise, some athletes have tried using glycerol or other plasma expanders however, this practice has been shown to increase urine output without improved performance. Additionally, they are now banned by the World Anti-Doping Agency (WADA) and are therefore not recommended.

Fluid and Sodium Needs During Exercise

Maintaining hydration status during exercise and competition is one of the most important nutritional strategies for any performance athlete. Doing so will help maintain heart rate, stroke volume, cardiac output, skin blood flow, core body temperature, rating of perceived exertion (RPE), and overall performance. You are probably aware of the health risks associated with heat stress and heat illness due to exercising in extreme heat, but performance will generally suffer as a result of dehydration long before those two dangerous conditions become a concern. In addition, many athletes do not fully comprehend the far-reaching adverse effects of dehydration including exacerbated strain on our cardiovascular system, decreased blood flow to the brain, elevated core temperature, increased skeletal muscle glycogen use, increased fatigue and decreased mood and brain function (Sawka, Cheuvront, and Kenefick 2015). Fluid losses will generally be lower when you are exercising in a cooler environment, as will your body’s tolerance for withstanding the state of underhydration (ACSM et al. 2007). However, environmental heat stress increases our body’s sweat rate response and fluid losses through our skin to keep our body cool. When exercising in humid environments, our skin is damp, which decreases our initial sweat response, increasing the chances of our bodies overheating. Over time, a training response occurs as we acclimatise to training and racing in the heat by producing a higher volume of sweat to keep cool (ACSM et al. 2007).

Upon initial training, introduction to the heat, or anytime an athlete becomes acutely dehydrated, the body increases the sweat concentration of sodium and chloride in order to conserve fluids. However, over time, heat acclimatization occurs, leading to increased total sweat rate and decreased sodium content of sweat by up to 50 percent for any individual athlete (ACSM et al. 2007).

While neither sweat rate nor electrolyte concentration of sweat are predictable by knowing an athlete’s gender or age alone, an increase in ambient temperature results in a near-universal impairment in aerobic performance across all athletes (Sawka, Cheuvront, and Kenefick 2015). However, since the extent to which sweat rate and performance deterioration occur varies widely, each athlete’s output and needs require individual consideration and investigation. It is generally understood that most athletes’ hydration goal should be to customise their fluid replacement plan in order to prevent less than 2 percent loss of body weight due to sweat in order to prevent degradation in performance. Many studies have shown that a decrease of 2 to 7 percent of body mass consistently decreases endurance-training performance in distances beginning with 1,500 meters (Maughan and Shirreffs 2008). Performance deteriorates with dehydration even in temperate conditions but is greatly impaired when more than 2 percent body weight is lost, exercise session is longer than 90 minutes, or temperature exceeds 30°C (86°F).

Any loss of body weight exceeding 1 to 2 percent of pre-exercise weight requires further examination and discussion, since for most athletes, and especially for those performing in warm, hot, or high-altitude environments, even this seemingly small loss of body weight due to sweat has been shown to adversely affect performance (Sawka, Cheuvront, and Kenefick 2015). For example, time trial performance has been shown to decrease significantly in both male and female cyclists who were dehydrated to the point of having lost only 1 to 2 percent of their body weight (Logan-Sprenger et al. 2012; Logan-Sprenger et al. 2015). They found that well-trained male cyclists completed a 5-kilometer hill climb faster when dehydration was minimized to 1.4 percent body weight loss compared to 2.2 percent or greater body weight loss. The authors’ conclusion is that high-intensity performance cannot be maintained when about 2 to 3 percent dehydration occurs. Possible mechanisms for this include not only the dehydration itself, but also an accompanying increase in muscle glycogen use in dehydrated athletes over the two-hour cycling trial. During their studies, male athletes were found to increase muscle glycogen use by up to 24 percent, while female athletes were found to increase muscle glycogen use by up to 31 percent, which alone can limit performance. The authors also noted increased heart rate by 4 to 9 beats per minute beginning at 20 minutes into the trial and continuing throughout, increased whole-body stress and reported feelings of decreased concentration, headaches, and increased RPE during exercise (Logan-Sprenger et al. 2012).

Maintaining close-to-baseline body weight from before to after training or competition also helps athletes avoid consequences of dehydration. Severe hypohydration is a concern for all athletes, because anytime 6 to 10 percent of body weight is lost due to sweating or fluid losses the athlete is at high risk for decreased cardiac output, decreased sweat production (and thus increased body temperature), decreased blood flow to skin and muscle, decreased performance and function, and increased risk of heat illness and heat stroke (ACSM et al. 2007). See the table below for calculation of dehydration status by body weight.

Fluid and Body Weight Losses by the Numbers

Dehydration status	Resulting weight for 120 lb (54 kg) athlete	Resulting weight for 160 lb (73 kg) athlete	Resulting weight for 200 lb (91 kg) athlete
2% loss of body weight: maximum acceptable fluid loss for most athletes	117.6 lb (53.3 kg) (2.4 lb [1.1 kg] fluid loss)	156.8 lb (71.1 kg) (3.2 lb [1.5 kg] fluid loss)	196 lb (89 kg) (4 lb [2 kg] fluid loss)
3% loss of body weight: possible maximum acceptable fluid loss for anaerobic sports, cold weather, technical skill sports	116 lb (54 kg) (3.6 lb [1.6 kg] fluid loss)	155.2 lb (70.4 kg) (4.8 lb [2.2 kg] fluid loss)	194 lb (88 kg) (6 lb [3 kg] fluid loss)
6% loss of body weight: severe dehydration	112.8 lb (51.2 kg) (7.2 lb [3.3 kg] fluid loss)	150.4 lb (68.2 kg) (9.6 lb [4.4 kg] fluid loss)	188 lb (85 kg) (12 lb [5 kg] fluid loss)

Postexercise Rehydration

In general, fluid balance can be returned to normal with adequate food and fluid intake during the 8 to 24 hours following an exercise session (ACSM et al. 2007). In order to restore euhydration during this time, athletes need to drink 125 to 150 percent of total fluid lost to sweat during exercise over the six hours immediately following completion of exercise (Shirreffs 1996). (See the table below for postexercise fluid guidelines.)

Postexercise Fluid Intake Guidelines

Goal	Guidelines (how to)	Time frame	Notes
Replace fluid lost to sweat during exercise	Athletes must replace 125-150% of fluid lost during each session within 2 hours postexerciseDrink 1.25-1.50 L of fluid per kg of body weight (20-24 oz/lb) lost during exercise	Within four to six hours after training session or competition	Include fluids and foods with salt to taste to help stimulate thirst and promote rehydration and fluid retention

In addition, following strenuous or prolonged exercise sessions, plain water will not be as effective at rehydrating as a food or beverage containing sodium and may not correct the fluid deficit as efficiently. Studies show that attempting to rehydrate with plain water alone (and without salty foods to help the body hold on to much-needed water) only serves to decrease the drive to drink, and stimulates urine output, which can prolong the period of time to restore fluid balance by three times (Shirreffs et al. 1996). The ACSM Position Statement (ACSM et al. 2007) says that fully replacing fluid and electrolyte deficits may require “aggressive” rehydration depending on the magnitude of the deficit and goal and timing of the next session. After exercise, athletes can often tolerate beverages with high sodium concentrations and should be allowed and encouraged to self-select such beverages as long as they are palatable to promote optimal rehydration for each individual (Shirreffs 1996). If an athlete has less than 12 hours to recover between sessions, he will need to actively seek to rehydrate by taking in 1.5 litres of fluid per kilogram of body weight (23 oz/lb) lost to sweat during exercise over the first six hours immediately after completion of exercise. Failure to replace sodium as well as fluids only leads to increased urine production rather than rehydration.

Summary

This post has been adapted from Lauren Antonucci’s High-Performance Nutrition for Masters Athletes and provides guidelines on how athletes can stay hydrated for optimal performance, before, during and after exercise.