An athlete’s sweat loss needs to be determined in order to prepare a fluid intake plan for optimal performance. Sweat loss can be determined by weighing athletes before and after exercise. Each kilogram of weight loss indicates one litre of fluid loss. Adding the amount of fluid consumed during the exercise session, gives total fluid loss for the session. For example, if an athlete finishes an exercise session one kg lighter and has consumed one litre of fluid during the session, total sweat loss equals two litre. Once the fluid loss is determined one has to choose the right drink to replenish the body.
Physical activity also depletes the body carbohydrate stores as liver and muscle glycogen are used up. Dehydration and carbohydrate depletion are two factors that limit prolonged physical activity.
The Right Drink
The choice of drink will depend on whether the primary aim is to rehydrate (keeping the body cool and maintaining fluid balance) or the replenishment of energy (restocking sugar and electrolyte stores) or both. In order to have the desired effect the drink needs to be absorbed efficiently. There are three main factors which affect the uptake of a drink or fluid in the body –
1.The osmolality or the concentration of dissolved particles in a fluid. Fluids are absorbed through the gut and into the bloodstream faster when their osmolality closely matches that of body fluids such as blood. Sports drinks contain dissolved minerals (sodium, etc.) and carbohydrates and therefore reach the bloodstream quickly.
2.Ability to maintain fluid balance - Sodium and other nutrients also play important role in regulating fluid balance in the body. In other words, they help determine how much fluid enters into muscle fibre and other cells and how much remains in the blood. Again, because sports drinks contain these nutrients, they do a better job of allowing the body to maintain optimal fluid balance, which is an important aspect of hydration.
3.Stimulation of thirst - Sodium content of sports drinks stimulates thirst, so athletes usually drink more when they have a sports drink than when they have plain water.
Glucose in the sports drink prevents blood glucose levels to fall too low and also helps to maintain body’s glycogen stores. Sodium and potassium are the main electrolytes which help maintain the hydration and reduce urine output. Thus, a sports drink rehydrates and improves performance too.
Timing the Sports Drink
Sports drink should be taken before, during and after the activity.
Before Exercise - Sports drinks are ideal one hour before the exercise as they help in building up muscle fuel i.e. the glycogen stores and the electrolytes reduce urine loss before the exercise.
During the Exercise - Sports drinks designed for use during exercise provide optimal fluid and fuel delivery. They help the athlete to perform better (peak performance) and last longer (endurance).
After Exercise – Post-exercise drinks help in recovery through effective rehydration.
Choosing the Right Sports Drink
Adequate evidence from extensive research on best drinks during exercise has helped to design sports drinks to provide the right balance of carbohydrate and fluid, to ensure that they are emptied quickly from the stomach and are rapidly absorbed from the small intestine.
Table 1. Ingredients with documented benefits for enhanced physical activity
|
Macronutrients |
Vitamin/Minerals |
Botanicals/ Phytochemicals |
|
Carbohydrate |
Leucine |
E. senticosus (Ginseng family) |
|
Protein |
Taurine |
R. rosea (Golden root or Rose root) |
|
Lipid |
ß-alanine |
Caffeine |
|
|
N-acetylcysteine |
Green tea |
|
|
Creatine |
Guarana (also called Brazilian coco) |
|
|
Vitamin B-Complex |
Flavanoids |
|
|
Vitamin D |
|
|
|
Iron |
|
|
|
Vitamin C |
|
|
|
Magnesium |
|
|
|
L-Arginine |
|
Table 1 lists the general nutritional requirements of athletes. Athletes' needs depend on their fitness level, type of training, body size and composition, and performance goals.
The endurance athletes who train aerobically (bicycling, walking on a treadmill, swimming etc.) for an hour or more at a time require a lot of energy. Since muscles prefer to burn carbohydrates for fuel, serious endurance exercisers need them in abundance. When muscle glycogen levels go down, the body may resort to burning protein for energy. This makes exercise tough and results in fatigue.
Resistance Exercisers are those primarily involved in strength training like weight lifting activities. They do primarily anaerobic exercise and do not burn as many calories as endurance athletes. They need simple carbohydrates to meet instant energy needs. Their protein needs depend on whether or not they are trying to build or maintain muscle mass.
Role of Various nutrients in Sports Drinks
Carohydrates - These are the fuel source for muscles and the brain, and contribute to the palatability of sports drinks. Ideally the carbohydrate concentration of a sports drink should not exceed 8%, or even be slightly less. High carbohydrate solutions can impair gastric emptying during exercise. Most commercially available sports drinks contain 6 to 8% carbohydrates. The type and amount of carbohydrates used in sports drinks varies and depends on factors such as taste, osmolarity (concentration of individual particles) and gut tolerance. New formulas contain “multiple transportable carbohydrates” - a blend of carbohydrates such as glucose and fructose which are absorbed from the intestine through different transport mechanisms. The purpose of such mixtures is to overcome the usual limitation on gut uptake of glucose-based sugars which occurs at rates of approximately 60 g/h. Studies have shown that when carbohydrates are consumed at high rates (> 60 g/h) during exercise to meet the requirements for prolonged strenuous events, these drinks are more effective than only glucose-based products in maintaining gut comfort, promoting muscle carbohydrate oxidation and enhancing performance.
Protein - Considerable scientific evidence is available to show the potential benefits of milk-derived whey protein on exercise-induced metabolism and physical performance. It has been found to be effective in both endurance training/activity and resistance training. In a randomised, double-blind, placebo-controlled study ingestion of extra protein (30 g/day) increased lean body mass in endurance training. Another study conducted on athletes involved in resistance training showed increased whole body protein turnover and improved post-exercise muscle recovery on an iso-caloric beverage containing 40 gm carbohydrates plus 20 gm whey protein versus that containing 60 gm of carbohydrates alone.
Electrolytes – Most sports drinks have added electrolytes namely sodium and potassium. The addition of sodium to sports drinks does have potential benefits. Sodium containing beverages can encourage fluid intake by driving the thirst mechanism. Sodium also increases fluid absorption and retention. Sports drinks may also help with salt replacement for athletes who are heavy or salty sweaters. Most commercial sports drinks contain sodium in the range of 10-25mmol/L and even lower in some sports waters. These drinks are not suitable when fluid replacement is crucial to subsequent performance (rehydration in a short period of time). Higher than usual sodium concentrations are needed to restore fluid balance and reduce urine losses during the reversal of moderate-severe dehydration. They may also be needed to replace sweat sodium losses during exercise in situations of high losses i.e. in salty sweaters or during prolonged exercise. Potassium is yet another important electrolyte and is found in higher amounts within the cells than in extracellular fluid including blood. Substantial amount of potassium is lost (100 – 200 mg/ hour in an adult) during physical activity and can induce muscle injury. There is paucity of evidence on beneficial role of magnesium.
Antioxidants - Exercise results in the production of reactive oxygen species (free radicals) that can potentially have damaging effects on muscle. This has led to investigations of the potential benefits of antioxidants on physical performance. These studies have shown some benefit of antioxidant administration in the form of N-acetylcysteine (NAC) on reducing exercise-induced muscle fatigue during endurance training. NAC provides the amino acid cysteine to the body, which can be used to synthesise an important intracellular antioxidant molecule called glutathione. Dietary antioxidants, such as the essential micronutrients vitamin C, beta-Carotene (vitamin A) and vitamin E, are also of general benefit to the body and consuming healthy diets rich in fruits and vegetables or containing fortified products can help to supply these important nutrients. Therefore, fruit juices.
Flavour - Flavour in a sports drink improves palatability and intake. It has been shown that fluid intake via a sports drinks is significantly better when compared to plain water due to the taste. Data from majority of scientific studies where a fixed volume of fluid is consumed may be misleading as in everyday situations intake is determined by the interaction of physiological and psychological factors. When the effect of palatability, together with the solute content of beverages in promoting rehydration after sweat loss was studied the results demonstrated the importance of palatability for promoting consumption but also confirmed that moderately high electrolyte content is essential if the ingested fluid is to be retained in the body. The benefits of the higher intake with the more palatable drinks with higher electrolyte content were lost because of the higher urine output.
Bioactive Compounds - E. senticosus is a species of small, woody shrub that is native to Eastern and Northeastern Asia (China, Korea, Japan, and Russia) and has been incorporated into sports drink as an anti-fatiguing agent. R. rosea is a botanical that has been reported to promote fatty acid metabolism and to improve body resistance to exercise. Flavonoids are bioactive phytochemicals and are incorporated into products or supplements to help promote greater endurance and stamina. Guarana is an increasingly popular ingredient from a South American plant found in the Amazon basin region. Guarana has a high concentration of caffeine in its seeds. This property has led to its inclusion in many energy shots or other energy-promoting beverage products. Due to its caffeine content, drinks containing guarana will help reduce fatigue and improve alertness. However, caution needs to be exercised as excess of caffeine from any source, can increase heart rate, and cause irritability and tremors. Green tea contains flavonoid compounds called catechins that have antioxidant properties and improve post-exercise recovery. Some evidence suggests catechins may also promote fat burning and improve maximal oxygen utilisation during exercise. Fruits namely tart cherries and berries are rich in flavonoids and anthocyanins that effectively suppress inflammation by blocking the production of inflammatory compounds and inhibit enzymes that increase pain and inflammation in the body.
Other Ingredients - Some beverages marketed as sports drinks have other added ingredients like vitamins, minerals, protein and herbs. Added antioxidants (Vitamin A, E and C) are reported to have enhanced recovery from post-exercise muscle injury. Protein or amino acids (2% or 2 g/100 ml) have shown to enhance performance. Some studies show that sports drinks providing protein/amino acids are superior to carbohydrate-electrolyte drinks in enhancing performance or recovery during prolonged exercise. The taste and temperature of sports drinks are also important factors in meeting hydration goals. Studies show that athletes more closely match fluid intake to sweat losses when offered flavoured sports drinks compared to water. Cool fluids are generally more palatable for athletes who are exercising in hot conditions. Sports drinks served in slush (ice slurry) form before and during- exercise have a comforting effect and better thermoregulation during activities undertaken in hot environments.
Conclusion
A properly formulated sports drink taken at appropriate junctures during the course of physical activity not only hydrates but also provides fuel for sustained performance and hastens post-exercise recovery for better performance subsequently.
