Hydration and Recovery

In order to optimize athletic performance, it is essential to consume adequate amounts of fluid before, during, and after competition (ADA & ACSM, 2000).  Water is a vital component of life; it supports anabolic and catabolic cellular processes, regulates temperature, and it is a major component of the body, surrounding organs, tissues, and cells (ACSM 2007).  Maintaining fluid balance impacts reaction time, coordination, visual motor skills, arithmetic and mental capacity (Baker, Conroy, & Kenney, 2007). As a result, imbalances in fluid and plasma levels are associated with continuous impairments in performance and life threatening injuries, including heat stroke (Baker, Conroy, & Kenney, 2007; ACSM 2007).  During skeletal muscle contraction, as the core body temperature rises, the primary way to dissipate the heat is through sweat loss.  Hydration methods are dependent on the sweat response rates, which can be impacted by various factors including: environmental conditions, physical status, and equipment or clothing attire (ACSM 2007).  After competition, fluid ingestion should be adjusted to enhance gastric emptying, absorption, and the rate of recovery (Evans, Shirreffs, & Maughan, 2011).       

Total body water (TBW) concentrations averages about 60% of the body mass and concentrations are higher in muscle than adipose tissue.  As a result, trained athletes usually have higher muscle mass, lower body fat, and higher TBW concentrations than untrained individuals.  The body is composed of various fluid compartments, including extracellular, fluid between cells, and intracellular fluid, located within cells.  The kidneys maintain water balance and regulate extracellular fluid through urine excretion that ranges between 20 to 1,000 mL/h (ACSM 2007).  Within the body, the daily water balance is equivalent to the difference between water gain and water loss by metabolic processes  (Nolte, Noakes, & van Vuuren, 2010; ACSM 2007).  Water gain accounts for the production of water during substrate oxidation, exogenous ingestion of water containing substances, and during cellular metabolism, including the breakdown of glycogen stores in the muscle and liver (Nolte, Noakes, & van Vuuren, 2010).  During physical activity, metabolic heat is produced and transferred from the working muscles, to the blood, body core, skin, and then released into the environment through sweat glands.  Even though, sweat glands are able to reabsorb sodium and chloride concentrations, it is not proportional to the sweat rate so refueling of electrolyte and fluid levels are imperative (ACSM 2007).    

During exercise, the magnitude of fluid loss is influenced by exercise, ambient temperature, and individual characteristics, such as body weight, training status, and gender (ADA & ACSM, 2000).  The average sweat rate is between 0.5 and 2.0 L/h and electrolyte losses are related to the sweat volume and its electrolyte concentrations, especially sodium and chloride.  Heat acclimization actually improves sodium and chloride reabsorption and it is associated with lower sodium concentration for a given sweat volume, thereby enhancing the sweat rate  (ACSM 2007).  Sweating is a regulatory response for evaporative cooling so prolonged exercise in heated environmental conditions increases the core temperature, heart rate, and sweating response (Gonzalez-Alonso, Calbet & Nielsen, 1999).  In contrast, cooler temperatures would decrease the sweating response and slight dehydration in this environment would not impair the body to the same degree as in heat (ACSM 2007).  Dehydration suppresses heat dissipation and the sweating response, which overtime raises the body temperature and may cause heat stroke (Gonzalez-Alonso, Calbet & Nielsen, 1999).  Additionally, wearing heavy equipment and clothing may elicit high sweating rates, while wet skin suppresses this response.  Therefore, fully padded and high body mass football players produce an average of 8.8 L/d of sweat and runners sweat at a significantly lower rate of 3.5 L/d.  These heavy sweaters are susceptible to dehydration, electrolyte and sodium losses, fatigue, and skeletal muscle cramps (ACSM 2007).  Due to differing diuretic responses, sweating is impacted by gender and males usually have higher rates than females.  Females reduce circulating Arginine Vasopressin (AVP) concentrations in response to osmolality fluctuations and this may lead to elevated renal water and electrolyte loses (Evans, Shirreffs, & Maughan, 2011; ACSM 2007).

Dehydration is directly related to physiologic strain by altering cardiovascular, thermoregulatory, metabolic, and nervous system functioning  (ACSM 2007).  It is associated with faster rates of fatigue due to glycogen depletion, lactate production, and higher perceived exertion responses during exercise (Gonzalez-Alonso, Calbet & Nielsen, 1999; Baker, Conroy, & Kenney, 2007).  Only a 2% change in the body weight caused by dehydration is critical; it is associated with reductions in short-term memory, mental alertness, and fine motor skills, like eye-hand coordination (ACSM 2007; Baker, Conroy, & Kenney, 2007).  As a result of fluid and electrolyte imbalances: muscle contractions, blood volume, blood flow, nerve impulses, autonomic regulation of the heart, and even hormones may be altered.  Reduced blood flow supply within the body and to the skeletal muscle is associated with a reduced substrate delivery of free fatty acids (FFA).  This shifts energy utilization and causes increased lactate concentrations and glycogen utilization (Gonzalez-Alonso, Calbet & Nielsen, 1999).   

After exercise, the goal is to replenish all fluid and electrolyte losses and the ingestion of 1.5 L per kilogram of body weight lost is recommended.  In order to improve palatability of the fluid, the following components should be considered: temperature, sodium (20-30 mEq/L), and flavoring for taste (ACSM 2007).  In addition, the fluid volume, electrolyte concentrations, and the amount of macronutrients in the fluid replacement beverage, should be adjusted to facilitate gastric emptying and intestinal absorption.  Upon consumption, the rate at which the fluid leaves the stomach and enters the intestine is gastric emptying.  Gastric emptying is dependent on osmolality and high osmolality inhibits gastric emptying, while low osmolality promotes absorption.  The rate at which fluid is absorbed and carbohydrates and electrolytes enter the blood stream from the intestines is intestinal absorption and this is dependent on the type and amount of carbohydrates in the fluid (Evans, Shirreffs, & Maughan, 2011).  The optimal amount of carbohydrate for rapid fluid replacement ranges between 6-8% (30-80 g/h) and amounts greater than 8% will delay gastric emptying and compromise fluid replacement  (ACSM 2007).  Research by Currell and Jeukendrup suggest that the coingestion of multiple carbohydrate sources at one gram per minute is absorbed faster than one single source (2008). According to Table 1, the G-2 and Powerade Zero beverages are not sufficient in carbohydrates and the Gatorade Protein Shake exceeds the recommended percentage of carbohydrates.  The most expensive product is the Gatorade Protein Shake and it is the only beverage that contains multiple carbohydrates and has a ratio of carbohydrate to protein is three to one.  All of the other drinks supply adequate sodium and potassium amounts and are within the recommended range of carbohydrate percentage of 6-8%.

Table 1

Beverage	Calories	CHO	CHO (g)	Type of CHO	FAT (g)	PRO (g)	Na+ (mg)	K+ (mg)	Cost
Zinco (14 fl oz)	120	6%	24	Sucrose	2	1	140	600	$2.49
Powerade (12 fl oz)	80	6%	21	High fructose corn syrup	0	0	150	35	$0.89
G-2 (8 fl oz)	20	2%	5	Sucrose	0	0	110	30	~$0.89
Powerade Zero (12 fl oz)	0	0%	0	Sucralose	0	0	150	35	$0.89
Gatorade Protein Recovery Shake (11.16 fl oz)	270	13%	45	Maltodextrin, sucrose and sucralose	1	20	320	540	$2.69
Ideal Recovery Drink		~6%	14g	Combination of all types of CHO			100	28

Overall, sweat rates vary depending on the exercise mode, intensity, and other conditions.  In order to sustain performance, replacement of electrolytes and clued volumes is important to avoid the detrimental effects of dehydration.  The carbohydrate amount, fluid volume, electrolyte concentrations, palatability components, and osmolality of the fluid should be considered to enhance fluid absorption.  

References

American Dietetic Association (ADA) & American College of Sports Association

(ACSM). (2000). Position of the American Dietetic Association, Dietitians of Canada, and the American College of Sports Medicine: Nutrition and athletic performance. J Am Diet Assoc., 100, 1543-1556.

American College of Sports Association (ACSM). (2007). American College of Sports

Medicine Position Stand: Exercise and fluid replacement. Med. Sci. Sports

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Baker, L., Conroy, D., & Kenney, W. (2007).  Dehydration Impairs Vigilance-Related

Attention in Male Basketball Players. Med. Sci. Sports Exerc., 39, 976–983.

Currell, K. & Jeukendrup, A. (2008). Superior Endurance Performance with Ingestion of

Multiple Transportable Carbohydrates. Med. Sci. Sports Exerc., 40, 275–281.

Evans, G., Shirreffs, S., & Maughan, R. (2011). The effects of repeated ingestion of high

            and low glucose–electrolyte solutions on gastric emptying and blood 2H2O

            concentration after an overnight fast. British Journal of Nutrition, 106, 1732–1739. González-Alonso, J., Calbet, J., & Nielsen, B. (1999). Metabolic and thermodynamic

            responses to dehydration-induced reductions in muscle blood flow in exercising

            humans. Journal Physiol, 520, 577-589.

 Nolte, H., Noakes, T., & van Vuuren, B. (2011). Protection of total body water

content and absence of hyperthermia despite 2% body mass loss (‘voluntary

dehydration’) in soldiers drinking ad libitum during prolonged exercise in cool

environmental conditions. Br J Sports Med, 45, 1106–1112.