Current and Potential Practices in Athletic Training

The Effects of Hydration on Athletic Performance

Meredith Decker
California University of Pennsylvania

Abstract

Hydration not only involves providing the body with enough fluids to function during exercise but also to prevent subsequent injuries and illnesses. By educating athletes and providing them with fluids during practices and competitions, certified Athletic Trainers’ can ensure that athletes will be properly hydrated and will not encounter further complications due to dehydration. The purpose of this paper is to give emphasis to the topic of hydration and the importance of incorporating fluids regularly into an athlete’s daily routine to ensure the best athletic performance.

Pre-Practice Hydration

Beginning practice or competition with an adequate hydration level is nearly as important as maintaining that hydration during exercise. By preparing oneself for practice or competition by hydrating, the athlete will have less hydrating to do during an event when compared to an athlete who is dehydrated. When a hypohydrated (under hydrated) athlete begins to exercise, physiologic mechanisms are compromised. The extent of the dysfunction is related to the degree of thermal stress experienced by the athlete. To ensure proper pre-exercise hydration, the athlete should consume approximately 500 to 600 mL (17 to 20 fl oz) of water or sports drink 2 to 3 hours before exercise (Casa et al., 2000). By hydrating several hours prior to the exercise, there is sufficient time for urine output to return toward normal before starting the event (Sawka & Burke, 2007).

On the other hand, hyperhydrating before exercise, accompanied by glycerol, may enhance thermoregulatory function and limit the performance decrements normally noted with dehydration while exercising in the heat specifically (Casa et al., 2000). Hyperhydration can be achieved by overdrinking combined with an agent that “binds” water within the body. These binding agents include glycerol and hypertonic drinks that can maintain hyperhydration for varied durations. Simple overdrinking will usually stimulate urine production and body water will rapidly return to euhydration, or a normal state of hydration, within several hours; however this compensatory mechanism is less effective during exercise and there is a risk of dilutional hyponatremia, which is a deficiency of sodium in the blood (Sawka & Burke, 2007).

Dehydration and its Negative Effects on Exercise

Dehydration is defined as a dynamic loss of body water or the transition from euhydration to hypohydration, otherwise known as dehydration. During exercise, hypohydration is associated with an increase in core body temperature and cardiovascular strain and a decrease in stroke volume and serum sodium levels (Volpe, Kristen, & Bland, 2009). Dehydration is most commonly seen after exercise in which heavy sweating has occurred (Opplinger & Bartok, 2002). A side effect of sweating is the loss of valuable fluids from the finite reservoir within the body, the rate being related to exercise intensity, individual differences, environmental conditions, acclimatization state, clothing, and baseline hydration status (Casa et al., 2000).

Dehydration of 1 percent to 2 percent of body weight begins to compromise physiologic function and negatively influences performance. Dehydration of greater than 3 percent of body weight further disturbs physiologic function and increases an athlete’s risk of developing an exertional heat illness (ie., heat cramps, heat exhaustion, or heat stroke). Dehydration initiates a cascade of events in which blood volume decreases, causing a compensatory increase in heart rate, followed by a decrease in stroke volume due to the increased heart rate and decreased filling time of the heart (Casa et al., 2000).
A major consequence of dehydration is a noted increase in core temperature during physical activity (Godek et al., 2006). Core temperature raises an additional 0.15 to 0.20 degrees Celsius for every 1 percent of body weight lost due to sweating during activity. This thermal strain also influences a greater cardiovascular strain. One example of the changes in the cardiovascular system is a rise in heart rate by an additional 3 to 5 beats per minute for every 1 percent of body weight lost. Further injury to the musculoskeletal system is also present. These changes include increased rate of glycogen degradation, elevated muscle temperature, and increased lactate levels. Studies investigating the role of dehydration on muscle strength have generally shown decrements in performance at 5 percent or more hydration (Casa et al., 2000).

Proper Fluid Replacement to Maintain Athletic Performance

Ensuring adequate hydration includes initiating exercise in a euhydrated state and matching fluid intake to sweat rate during exercise (Osterburg, Horswill, & Baker, 2009). Fluid replacement should approximate sweat and urine losses and at least maintain hydration at less than 2 percent body weight reduction. This generally requires 200 to 300 mL (7 to 10 fl oz) every 10 to 20 minutes during exercise. Proper hydration during exercise will influence cardiovascular function, thermoregulatory function, muscle functioning, fluid volume status, and exercise performance (Casa et al., 2000). The goal of drinking during exercise is to prevent excessive dehydration (2 percent body weight loss from water deficit) and excessive changes in electrolyte balance to avert compromised exercise performance (Sawka & Burke, 2007). Fluid ingestion may also influence performance by delaying the evolution of core temperature by acting as a “heat sink.” An increased central drive and motivation may also be experienced by being well hydrated.

In an effort to examine hydration on different forms of exercise, such as strength, power, and resistance exercise, Judelson et al. (2007) studied seven healthy males. The subjects were tested under three conditions: euhydrated, hypohydrated by 2.5 percent body mass, and hypohydrated by 5 percent body mass. The subjects performed a vertical jump test, 1RM back squat, and a resistance exercise challenge that consisted of 10 reps per six sets. Under the hypohydrated conditions, subjects experienced a much higher core temperature, compared to the euhydrated condition under which more work in the first five sets were completed than the while hypohydrated. The biggest effect of hypohydration came during the resistance exercise challenge. It was also noticed that central activation of the CNS and PNS seemed to have been reduced, resulting in a more rapid fatigue. There was no significant difference in strength and power between the groups, however, vertical jump height increased as total body decreased regardless of group (Judelson et al., 2007).

Some, but not all, exercise is going to be affected by being hydrated or dehydrated. Athletes involved in shorter anaerobic exercises have less physiologic changes occurring and therefore can experience an increase in performance due to less body mass by being slightly hypohydrated. Longer, more aerobic exercises use more total body water and therefore need to be replenished during exercise. Replenishing the water stores will influence several factors and keep the athlete hydrated enough to perform at his or her best capabilities.

Post-Exercise Hydration and Preparing for Subsequent Exercise

Although hydration before and during exercise is essential for good athletic performance, hydration after exercise is equally as important. A high rate of fluid consumption during the first two hours of post-exercise rehydration is known to increase plasma volume significantly and to result in substantial urine production (Kovacs et al., 2002). Individuals looking to achieve rapid and complete recovery from dehydration should drink 1.5L of fluid for each kilogram of body weight loss (Sawka & Burke, 2007).

Post-exercise hydration should aim to correct any fluid loss accumulated during the practice or event. Rehydration should include water to restore hydration status, carbohydrates to replenish glycogen stores, and electrolytes to speed rehydration. The primary goal is the immediate return of physiologic function, especially if an exercise bout will follow. Based on volume and osmolarity, the best fluid to drink after exercise to replace fluids that are lost via sweating may not be water. Including carbohydrates in the rehydration solution may improve the rate of intestinal absorption of sodium and water, and aid in replenishing the glycogen stores. Replenishing the glycogen stores can enhance performance in subsequent exercise sessions (Casa et al., 2000). It is important to keep in mind the recommended daily values for carbohydrates and to not exceed those limits while rehydrating.

Summary

Beginning a practice or competition in a severely hypohydrated state will negatively affect performance. Dehydration influences several aspects of exercise in a negative way. Rises in core temperature, early fatigue, and decreased performance are some factors that are present in a dehydrated athlete. Understanding the signs and symptoms of dehydration and managing it early will stop any further injury or illness to the athlete. Certified Athletic Trainers’ must promote hydration before exercise but must also be knowledgeable of the signs and symptoms of dehydration in the event that it occurs. Although water is the primary method of rehydration, sports drinks can be incorporated before, during, and after exercise in order to maintain fluid balance. Proper hydration during exercise is known to have benefits that aid in athletic performance. Overall hydration is beneficial not only to exercise and athletic performance but also physiologic functions.

References