Nutrition and Exercise Performance Flashcards
Overview
- Dietary carbohydrate and muscle glycogen
- Dietary fats and use of fat during exercise
- Protein needs for the athlete
- Fluid intake during and following exercise
- Recovery nutrition
Classes of nutrients
- Carbohydrate (CHO)
- Fat (lipid)
- Protein
- Vitamins
- Minerals § Water
questions to help devise nutritional strategies for an athlete:
- What is the duration (and thus the intensity of the exercise involved)?
- What are the environmental conditions?
- What is the training status of the athlete?
- What has been the success of prior nutritional strategies?
facts
- higher intensity more glycogen, lower intensity more fat
- exercise in heat, greater use of muscle glycogen due to catecholamine -will heat wall quickly
- muscle fibres increase, endurance athlete can burn more fat and delay hitting wall
- composition of sport drink (during or after exercise) - individual
nutritional factors associated with exercise-induced fatigue include:
- Glycogen depletion
- Hypoglycemia
- ‘Central’ fatigue
- Dehydration
- Hyponatraemia
Carbohydrate
monosaccharides
disaccharide
polysaccharide
- glucose mainly used for brain and CNS
Glycogen depletion
hitting the wall - run out of glycogen in muscles being used
Hypoglycemia
Low Blood glucose - primary effect - loss of motivation and concentration
‘central fatigue’
Fatigue that originates in brain
Dehydration
Lead to heat stroke, coma or even death (medical condition)
Hyponatraemia
- low plasma sodium concentrations - associated with prolonged exercises and who drink too much fluid (diluting sodium in blood) - medical condition
Sources of Carbohydrates
- grains
- fruits
- vegetables
- milk
Carbohydrates
- stored in body as glycogen
- highest storage in liver (to maintain blood glucose levels)
dietary carbohydrate intake
- for athletes is essential, given the critical role that muscle glycogen plays in exercise
Muscle glycogen
- a unique fuel, as it can be used both aerobically (with oxygen) and anaerobically (without oxygen)
- In contrast fat (which is the other main fuel used by exercising muscles) can only be used with oxygen
Glycogen stores
- dietary carbohydrate intake should constitute at least 50% of the total calories consumed every day
- heavy training and endurance exercises, should be ideally around 55-60%
e.g.
For an athlete consuming 3000 calories a day, 55-60% from CHO would equate to 1650-1800 calories (400 and 450 grams a day)
Percentages not usually used
%’s need to be balanced against total energy intake when CHO needs of athletes are considered; athletes who consume large amounts of energy per day may meet their maximal rates of glycogen resynthesis with CHO representing only 40% of the total energy.
Muscle glycogen resynthesis
- complete resynthesis can take up to 24 hours
Pre-exercise glycogen ‘loading’
- aim of CHO or glycogen loading is to super-compensate or maximise muscle glycogen stores
- will delay fatigue and allow the exercising athlete to maintain moderate to high intensity exercise for longer
- original studies in the 1960’s showed clear and unequivacal benefits to a 7-day depleting repleting schedule to maximise pre-exercise muscle glycogen stores
- more recent work has shown that well-trained athletes can achieve the same ‘super-compensation’ of glycogen without the depleting phase (and just by tapering).
if seven days out from competition you would deliberately deplete glycogen levels on first day
3 days following high fat and high protein depriving muscles ability to resynthesis glycogen - making muscles desperate for carbohydrates that when store carbohydrates the next day get a super compensation
Taper
- reduce amount of glycogen cells
Pre-event intake of CHO
- To maximise muscle glycogen stores.
- To maximise liver glycogen stores.
- To ensure the athlete is adequately hydrated.
- To prevent hunger but to avoid gastrointestinal discomfort.
Glycaemic Index
- measure of the rate of digestion and absorption of carbohydrate foods and the resultant effect on blood glucose level
- CHO meals that have a low glycaemic index result in a slower rise in blood glucose response.
- However, research has not shown a significant difference in performance between high and low GI meals consumed before exercise.
High Glycemic Index
- it would be bad as glucose spike, insulin then released which suppresses release of fat into blood which isn’t beneficial to exercise
- catecholamines blocks insulin therefore can take high glycemic index
- what actually happens is
Priorities during prolonged exercise
- Substrate replacement (prevention of hypoglycemia and sparing of muscle glycogen). This is likely to delay but not prevent fatigue
- Fluid replacement
The choice of food and drinks to be consumed during exercise should be closely related to the distance and intensity of the race and also to environmental conditions.
- max sweating twice rate of fluid replacement
- post exercise - max sweating twice rate of fluid replacement
mechanisms as to performance improved with CHO intake during exercise
- not clear, muscle glycogen sparing may occur (if does probably only in type 1 fibres)
- In addition, CHO taken during exercise better maintains blood glucose concentrations
CHO: a ‘central’ influences
CHO ingestion during exercise can improve mental performance as well as exercise capacity.
Indeed, CHO intake during exercise appears to improve performance independent of glycogen depletion – suggesting a central (CNS) effect.
Fat
- an essential component of cell membranes and nerve fibers
- a primary energy source
- protects organs
- stores the fat-soluble vitamins
- necessary for steroid hormone production
- provides insulation
- isn’t critical
mechanisms as to performance improved with CHO intake during exercise
- not clear, muscle glycogen sparing may occur (if does probably only in type 1 fibres)
- In addition, CHO taken during exercise better maintains blood glucose concentrations
CHO: a ‘central’ influences
CHO ingestion during exercise can improve mental performance as well as exercise capacity.
Indeed, CHO intake during exercise appears to improve performance independent of glycogen depletion – suggesting a central (CNS) effect.
Fat
- an essential component of cell membranes and nerve fibers
- a primary energy source
- protects organs
- stores the fat-soluble vitamins
- necessary for steroid hormone production
- provides insulation
Protein
- 20 amino acids required by the body, 8 have to be gained from the diet.
- There is an insulin response to EAA intake and insulin + AA’s are together important for increasing protein synthesis.
- Amino acids and protein contribute to structure, transport, enzyme function, hormone production, immune function, acid-base balance, fluid balance and energy availability.
Fat intake and exercise performance
- in four days muscles would adapt to store more fat - muscles increase capacity to burn fat (oxidative phosphorylation) and decrease capacity to burn glycogen
- reduce rate at which muscle glycogen is used and can delay athlete hitting the wall
Challenges on low CHO diet
- potential to undertake high exercise intensity
- for endurance athlete in training exercising for a couple of days a week on low CHO diet may be valuable
- must precede competition
Protein
- 20 amino acids required by the body, 8 have to be gained from the diet.
- Amino acids and protein contribute to structure, transport, enzyme function, hormone production, immune function, acid-base balance, fluid balance and energy availability.
BV
Biological value
Protein amount for athletes
well trained endurance:
- between 1.2 and 1.6g · kg−1 · d−1
majority of athletes consume in excess of 1.8g · kg−1 · d−1
example
For example, take an athlete who consumes 6400 kcal/day. If 14% of this energy intake is protein, that corresponds to 2.5g · kg−1 · d−1 (for a large athlete) or 3.2g · kg−1 · d−1 for a smaller athlete.
Even when consuming 3500 kcal/day, a balanced diet will provide 1.6-1.9g · kg−1 · d−1 .
Whey protein
- Whey protein elicits a greater initial rate of protein synthesis than casein.
- Whey is a soluble protein that is quickly absorbed; casein clots in the stomach – leading to slower absorption.
- Also, whey has a higher leucine content and this may be related to the faster protein synthesis.
Leucine
- essential amino acid
- important in triggering muscle growth
- doesnt matter when take it
- has more whey than casein
- contained in nuts
- stimulate protein synthesis; as little as 6g will initiate synthesis; >20g does not appear to elicit any further effect.
daily intake of protein
- 20g 5-6 times a day
- timing is more important than daily intake for athletes seeking hypertrophy of muscles
- no adverse consequences
- supplementation does not confer any advantage or benefit
- older athletes might need more protein
Fluid intake
- in last 30mins will not benefit performance
- for endurance events fluid intake (especially when weather leads to sweating) will benefit
- can drop max 4kg due to prolonged endurance exercise (6% deficit in body water)
gastric emptying
- maximising is important
- high volumes of fluid favor
- keeping CHO concentration of sport drink below 6% will reduce risks of lowering GE
Beverages
gatorade is best?? half the sweetness of soft drink
Hyponatremia
- condition in which blood sodium concentrations are lower than 135-145mmol/L
- dilutes sodium in body
- from over-consumption of fluid during exercise
symptoms
- weakness
- disorientation
- seizures
- coma
nutrition for recovery after training and competition
- Between 6 and 24 hours often separate high intensity training sessions
- Nutritional issues relating to recovery include restoration of muscle and liver glycogen, rehydration and repair/growth of tissue
Glycogen Resynthesis
- Post-exercise muscle glycogen resynthesis is most rapid within 2-4 hours following exercise
- This is because glucose enters the muscle cell independent of insulin
- This means that once exercise has been completed, CHO intake must immediately begin
- muscles highly permeable to glucose
- there is a max amount of glycogen that muscles can store
Fluid replacement
- Athletes typically only replace 30-60% of fluids lost as a result of exercise
- 150% of the volume of lost fluid needs to be consumed – to replace the losses.
- Sodium concentrations need to be high in order to prevent post-exercise excessive urine loss. If sodium concentrations in the drink are low, more fluid will need to be consumed.
- Sports drinks contain 10-25 mmol/L of sodium – which is not high but keeps the drink palatable.
- Sodium-containing foods consumed post-exercise may lift the sodium concentration and assist in fluid retention.
