Dietary strategies that can be used to improve performance and recovery, including application of the glycaemic index, carbohydrate loading and gels, and supplementation with protein and caffeine
Hydration considerations to improve performance and recovery, including water, hypertonic, isotonic and hypotonic drinks and intravenous rehydration.
Discuss similarities and differences in a variety of performance enhancing, and recovery facilitating practices
Critique nutritional and hydration practices used to improve performances and assist recovery.
• For the first two hours during recovery blood is being blood is still being sent to muscles in large quantities and muscles are still receptive to taking up glucose and enzymes conducive to converting glucose to glycogen.
• High GI foods and sports drinks will provide glucose to muscles quickly.
Ranks foods from 0–100 according to how much they raise blood sugar over a two hour period, compared to pure glucose.
A GI score of 70 means this food will raise blood sugar by 70% s much as pure glucose in a two hour period.
Low GI foods consumed prior to participating in endurance activities (60+ mins) lead to minimal changes in blood glucose and insulin levels and lead to glycogen sparing.
Moderate GI foods consumed during endurance activities increase carbohydrate availability and enhance performance
High GI foods quickly replenish carbohydrate stores during recovery.
• sports drinks rehydrate, replace electrolytes and refuel carbohydrates• electrolytes are used by muscle, nerve and cardiac cells to maintain
voltages across their membranes and allow electrical messages to flow across them
• the higher the carbohydrate levels in drinks, the slower the rate of stomach emptying• electrolytes reduce urine output, enable fluid to empty quickly from the
stomach, promote absorption from the intestine and encourage fluid retention.
Isotonic drinksHave the same osmolality as the body’s own fluids, containing between 4–8 g of CHO per 100 mL. Glucose is the body’s preferred source of energy, so an isotonic drink where the carbohydrate source is glucose in a concentration of 4–8%, is an ideal choice for assisting in hydration.
Hypotonic drinksHave a low osmolality, containing the fewest carbohydrate and electrolyte particles. This drink is more diluted and therefore absorbed at a faster rate than ordinary water. Hypotonic drinks generally contain less than 4 g of CHO per 100 mL. They quickly replace fluids lost by sweating and are most suitable for athletes who need fluid without the added boost of carbohydrate or electrolytes. Hypertonic drinksHave a higher osmolality than the body’s own fluids, which means their absorption is slower than water. They contain approximately 8 g of CHO per 100 mL. They are normally taken after exercise to top up muscle glycogen stores. In ultradistance events they can be taken during exercise to meet the energy requirements. If consumed during exercise, hypertonic drinks need to be used in conjunction with isotonic drinks to replace fluids.
Oral vs. intravenous hydration• Oral hydration is the drinking and consumption of fluids via the mouth. • Intravenous (IV) hydration is the administration of fluid (typically a saline
solution, but may also contain glucose ) through a vein. • IV hydration has been used for fluid replacement where athletes have lost
consciousness, and/or are not able to drink usually after suffering performance stress or injury.
• IV hydration requires hygienic conditions for it to be administered and there is a danger of over hydration if not managed correctly which can cause kidney damage.
• The 2006 prohibited list of the World anti-doping code states that 'Intravenous infusions are prohibited, except as legitimate medical treatment'. This is a method that is 'prohibited at all times,' which means it applies 'in and out of competition'.
• All of the scientific literature reviewed reveals no added benefit of using IV rehydration methods, as opposed to oral hydration in mildly dehydrated individuals before and during activity. There was no benefit in regards to sporting performance, body temperature and fluid control.
Carbohydrate gels• Are essentially dehydrated sports drinks, i.e. concentrated carbohydrates
without the water. • For gels to be effective they must be consumed with water, otherwise
they will not be absorbed quickly enough to ‘top up' fuel stores.
• Gels provide the same benefits as sports drinks (when taken with water) and should be taken in the same circumstances: during workouts and events lasting more than an hour.
• Gels and sports bars taken together should be avoided when high sweat rates occur because of the large increase in carbohydrate concentration and resultant slowing of hydration rates.
Caffeine supplementation• WADA removed caffeine from the list of banned substances in
2004, but currently under review• Approx 60% of AFL footballers have taken caffeine tablets with
10% experiencing side-effects
Possible benefits include:• stimulation of central nervous and respiratory systems• glycogen sparing effect by enabling more fat to be used as a fuel earlier on
in performances thereby delaying fatigue• increases muscle cell permeability to Ca+ ions and resultant muscle
contractility
Side-effects include:• increased urine production (diuretic effect)• heart arrhythmia and palpitations• dehydration• gastric upsets• anxiety and dependence• restlessness
Creatine supplementationCreatine is an amino acid that occurs naturally in meat, eggs and fish
Creatine supplements usually consist of creatine monohydrate or combinations of alts such as creatine citrate or creatine pyruvate (Creatine salts are more soluble than creatine monohydrate and are often added to high performance sports drinks or gels)
Creatine supplements are mainly taken by sportspeople relying on speed, power and rapid/explosive muscles contractions (football, soccer, netball)
Possible benefits include:• increased post exercise glycogen replenishment• decreased reliance on anaerobic glycolysis• Stimulates protein synthesis and decreases protein breakdownSide-effects include:• gastric upsets• kidney problems• fluid retention• muscle cramps
Protein supplementationProtein supplements have long been used by athletes relying on power and strength and usually taken in powder form (easier to ingest compared to same quantity occurring in natural foods)
Protein:• provides the raw material for both muscle construction and repair (contact
sports)• promotes glycogen resynthesis• plays an important role in the immune system• is critical to the endocrine (hormone production) system• facilitates the transmission of nerve impulses throughout the nervous system• prevent sports anaemia by promoting an increased synthesis of
haemoglobin, myoglobin, oxidative enzymes
Protein is optimally absorbed through digestive processes of the small intestine 30-60 min after training or competition
Note – Excess proteins cannot be stored and are broken down and excreted – large quantities may place a significant strain on the kidneys
Commonly used as a buffering agent for athletes primarily calling upon their anaerobic glycolysis or LA system (taken in powder or tablet form)
• when lactate and H+ ions are produced there is a decrease in ATP breakdown causing decreased force and rate of muscle contractions
• buffering agents allow H+ ions to leave muscles at a faster rate allowing more lactate and H+ to be produced before muscle function is inhibited
• bicarbonate is the body’s most important extracellular buffer and it’s ability to dispose of excess H+ ions is thought to be better than that of citrate
• citrate has been deemed to be 'gentler' than bicarbonate and lead to less gastric upsets.
