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Nutrition in Sport
Transcript of Nutrition in Sport
-The pancreas determines when the amount of glucose in the blood is too low or too high. And the body does this unconsciously. When it is too low: When it is too high: -The condition is known as hypoglycemia.
-The pancreas produces a hormone (glucagon) to stimulate a release of stored glycogen from the liver, in the form of glucose, to go into the blood and restore the balance.
-It is important that people, especially athletes consume the right amount of carbohydrates (around 130g a day; slightly more for athletes); so that glucose isn't taken from the muscles. -It is known as hyperglycemia.
-The pancreas releases the hormone insulin, to stimulate the liver to release less glucose.
-The glucose is converted into glycogen and is then stored in the liver or in the muscles. This brings the blood glucose levels down.
-When the muscle stores are full , the remainder is converted into fat (by LIPOGENESIS).
-Fat is easier to store than glucose. (World of sports science (2013). -The skeletal muscles have a storage volume of 1% for glycogen. Figure 1 -When glucose is going into the muscles to be stored it has to diffuse into the muscle cells and this is done by the 2 protein glucose transporters which are the following:
-GLUT1 when carbohydrate (CHO) is too low.
-GLUT4 when CHO is too high.
-Once it is inside, it then reforms to glycogen. -It is important that these stores are kept to the correct amount, as glycogen depletion is said to implicate muscle fatigue.
-It is also apparent that muscle glycogen availability can influence muscle metabolism and function, as well as having an effect on other metabolic and cellular processes.
-For example; low muscle glycogen is associated with;
reduced muscle, glycogenolysis, increased glucose uptake and protein degradation, accelerated
glycogen resynthesis, impaired excitation–contraction coupling, enhanced insulin action, and
the potentiation of the exercise-induced increases the transcription of metabolic genes. (Hargreaves M. (2004). Fat deposits: The fat that is stored in the body is stored as ADIPOSE TISSUE.
This is in the form of; -Subcutaneous fat; (which is the fat that we can feel around our bones and muscles).
-Visceral fat; (which is the fat that we can’t see, that surrounds our organs). And as mentioned in the previous slide; fat is a more efficient way of storing energy.
-Adipose tissue has the highest weight and calorific value with figures of 100,000, and muscle fat follows, with a calorific value of 2616. (Manore M., Mayer N., and Thompson J. (2009). Fat passes through the small intestine and bile that is released from the gallbladder breaks fat down into fatty acids and glycerol when energy demands are low.
-Fatty acids are stored in fat.
-Glycerol returns to the liver.
If energy demands are high, the broken down fats are taken into the cells that need it and used for energy. ... When not in use, fat is deposited where the body thinks it is needed and broken down fats are recombined by LIPOPROTEINS to form chylomicrons. They enter the lymphatic system and fat is carried around the body. -With active people; fat is more likely to be stored in the mitochondria to be used for energy.
-With sedentary people; fat is more likely to be stored in fat cells around the body.
-Some people are born with more fat cells.
-Some people eat too much fat.
-Fat has more energy than sugar. Since muscle makes up 20-30% of our body weight, we carry around 300-400 grams of muscle glycogen, which holds a calorific value of 1200-16000. (Williams M.H. (2005). And to maintain the desirable amount the body must make sure that the appropriate balance is kept between carbohydrate oxidation and carbohydrate consumption. (Manore M., Mayer N., and Thompson J. (2009), Pg. 35). -Liver glycogen plays an important role in maintaining blood glucose levels throughout the night, and this is why it is important that we have a good breakfast, to replenish the glycogen stores. (Manore M., Mayer N., and Thompson J. (2009), Pg. 35). -We have around 75-100 grams of liver glycogen and this has a calorific value of 300-400. (Williams M.H. (2005). Tools that can be used to measure energy intake and energy expenditure:
-Monitoring heart rate and maintaining an activity diary.
-Keeping a calorific log of food and drink consumed.
-Food frequency questionnaires.
-Metabolic chambers: calculate heat output and gas exhaled. You can measure the heat given off and calculate energy expenditure.
-Doubly labelled water technique: measures the turnover of hydrogen and oxygen into water and carbon dioxide; energy expenditure is then calculated from the difference. (Advanced Technology). These methods only provide estimated results (indirect calorimetry), as the more accurate methods involve a lot of preparation, time and money. Figure 2 Figure 3 Figure 5 Figure 4 -We need 300-400 grams of muscle glycogen in our bodies, so we need to keep our carbohydrate intake high, especially if we are physically active. -Stored glycogen is broken down into glucose followed by pyruvic acid (by the process of glycolysis).
-Lactate is recycled into glycogen through the Cori cycle.
-The pyruvic acid goes into the Krebs cycle, where oxidative phosphorylation takes place, generating ATP (Adenosine Triphosphate).
-The ATP then enters the electron transport chain which results in energy being generated. Anaerobic
Net: 6ATP. Aerobic
Net: 30ATP. So for every glucose molecule 36ATP can be generated. (Muscle Physiology (2000). -Fat is metabolized in the presence of oxygen.
-Stored fat is broken down by a hydrolysis reaction by Lipolysis, and they form glycerol (triglycerides) and fatty acids.
-Beta oxidation breaks down the fat in the mitochondria to make ATP and convert substances into Acetyl CoA.
-The fatty acids are converted into Acetyl CoA and go straight into the Krebs cycle.
-The triglycerides are converted into pyruvic acid, which again is converted into Acetyl CoA, which enters the Krebs cycle.
-Oxygen finally gets the electrons in the electron transport chain. (Clackamas (2001-2003). One 18 carbon fat molecule is said to yield 146 ATP. (Answers (2013). At rest and during exercise: Direct and Indirect Calorimetry: The 2 main substrates used in the body especially during exercise are, carbohydrates and fats. proteins can also be used to produce ATP energy for the human body.
it is estimated that at rest fats contribute to 41-67% , carbohydrates 33-42%, and proteins from just a trace to 17% of the total daily energy requirements of the human body (Lemon and Nagel, 1981). Optimizing muscle and hepatic CHO stores: Carbohydrate/glycogen loading: As carbohydrates are one of the main sources of exercise fuel, it is important that the levels of this substrate are kept topped up. The amount of carbohydrates available for the muscles and central nervous system becomes a limiting factor in the performance of prolonged sessions of sub-maximal or high-intensity exercise, so a lot of athletes try the procedure of carbohydrate loading. (Maughan R., Burke L., and Coyle E. (2005, Pg. 24-25). This can help maximize strength, speed and stamina and give the body the extra fuel it needs to keep going for longer.
-(Hargreaves 'et al' 1995) said that increasing dietary carbohydrate in the 1-7 days before exercise (competition) is generally associated with enhanced performance when exercise duration exceeds about 90 minutes. (Maughan R., Burke L., and Coyle E. (2005, Pg. 51).
There are now many regimes that you can follow although the newest and most appealing is the Western Australian Protocol: Type of carbohydrates ingested: Simple vs Complex: Benefits of this protocol: -It's a gradual progression of tapering.
-It's easy to maintain a normal dietary intake (which is more routine friendly).
-You only adapt the diet on the day before the race (where you deplete all glycogen stores before consuming all the CHO).
-The exercise on the penultimate day is of a short duration. -Simple carbohydrates are recommended to be consumed in events that require a fast source of energy for a short period of time.
-Examples include; weight lifting, sprinting. They are absorbed easily and provide a quick release of glucose.
-It is good to have simple carbs just before and during events, and these can be taken in the form of solids or liquids. E.g. Jelly babies, energy drinks and don't give you a bloated feeling. -Complex carbohydrates are better suited to those who compete in intermediate to long duration activities such as; marathon running and long-distance cycling. This is because they give you energy which is released slowly, allowing you to maintain stores for longer.
-They are however absorbed slowly too which means that they have to be consumed the night before or a few hours before the activity.
-Complex carbs tend to be more starchy foods like; bread, rice, potatoes, porridge etc. Solid vs Liquid: Solid and liquid carbs can be both simple and complex, and depending on the activity they can be taken prior to an event, during or after. Training and competition schedules affect which one is taken, as well as the type, length, intensity and nature of the sport. And of course environmental conditions and personal preference also has an impact on the type you consume. -For a sport like boxing it would be sensible to take solid complex carbs the night prior to the event and then take simple solid carbs and liquid carbs just before and during the event. Glycaemic Index & Glycaemic Load: Glycaemic Index: Indicates how fast and how high a particular food can raise our blood glucose (blood sugar) level. (The World’s Healthiest Foods (2001-2013).
-High GI foods get absorbed quickly into the blood stream and will normally prompt a high rise in blood glucose level.
-Low GI foods get absorbed slower but the effects last longer.
-During sports athletes tend to have moderate to high GI foods like; power bars, granola bars, energy gels, sports drinks, fruit and sweets which will raise their blood glucose level and provide them with around 30-60 grams of energy giving carbohydrate per serving.
-Taking high GI foods with protein or fat slows down the rate of glucose (energy) usage, and therefore it is recommended to try incorporating this combination into the diet. E.g. Porridge (low GI, with honey (high GI). It is good to have high GI foods post exercise in order to facilitate and speed up recovery and this table gives us some examples of what foods could be eaten. (Sunarja F. (2008). Glycaemic Load: Relates to the quantity of carbohydrates in food and what impact it has on the blood sugar levels. (Harvard (2013). This can be known as the quantity you have to consume before it has an impact.
-A food’s glycaemic load is determined by multiplying its glycamic index by the amount of carbohydrate it contains. Some glycaemic load food categories: Low (10 or under): Medium (11-19): High (20+): (Harvard (2013). -High fibre fruits and vegetables (not potatoes)
-Bran cereals (1oz)
-Beans and legumes (5oz) -Pearl barley (1 cup cooked)
-Brown rice (3/4 cup cooked)
-Oatmeal (1 cup cooked)
-Rice cakes (3)
-Whole grain breads (1 slice)
-Whole grain pasta (11/4 cup cooked)
-No added sugar fruit juices (8oz) -Baked potato
-Refined breakfast cereal (1oz)
-Sugar sweetened drinks (12oz)
-Jelly beans (30 small)
-Couscous (1 cup cooked)
-White basmati rice (1 cup cooked)
-White flower pasta (11/4 cup cooked) Depending on the type of lifestyle you live or the daily activities you take out, you might try to manipulate or direct your diet on eating certain foods to fit in with your schedule (and if an athlete, your training schedule). The glycaemic load will vary with each individual and the glyceamic index of foods will determine you nutritional choices.
Some athletes may even try to even out their glycaemic load by consuming foods and drinks high in protein with foods with a low GL, so as to have carbohydrate as the energy source with protein to build muscle and aid recovery. During Exercise various forms of each fuel are used to supply the working muscles with the additional ATP which is needed to sustain the movement. to understand which energy sources are used during exercise it is first necessary to know approximately how much of each energy substrate is available.
to start with little carbohydrate is stored, the amount stored in the human body is enough to support life for 1 1/4 days this is with muscle glycogen, liver glycogen and circulating glucose added together. which is why it is essential to replenish these carbohydrate stores regularly
exercise will also have a major impact on the length of time that each substrate can provide energy for. in general the lower intensity the exercise is the more important that fat is as a fuel, so the higher the intensity the exercise is the more important carbohydrate is as a fuel. the duration of exercise also has a similar effect. the shorter the duration the more important carbohydrate is as a fuel. the longer length of exercise sees fat being used more and more. fat comes into play as the duration of exercise lengthens because the glycogen stores deplete. There are 2 techniques that are employed under laboratory settings to measure the energy expenditure and substrate utilisation... Direct Calorimetry indirect Calorimetry direct calorimetry involves the measurement of heat that is produced during metabolism.
the energy used can be measured by installing a exercise devise in the chamber (such as a treadmill).
a thin copper sheet will line the interior wall of the insulated calorimeter were heat exchangers will be attached.
a measured amount of water will circulate the heat exchanger which will absorb the heat which is radiated from the individual exercising in the chamber. this will reflect the metabolic rate of that person
Direct measurement of heat production in humans is proven to be precise based upon the concept that 1 calorie = the amount of heat needed to raise the temp of 1g of water by 1 degree.
the limitations to this are the amount of time it would take to complete this procedure. there is also alot of equipment needed to complete this, and there would also be additional heat produced by the environment and exercise equipment that is in the chamber. indirect calorimetry is described as the method which the body's respiratory gas exchange is utilised to estimate the amount of energy produced through the oxidative process.
The thought behind this process is that all bioenergetic processes are oxygen dependant (Ravussin and Rising, 1992).
indirect calorimetry differs from direct calorimetry in the fact that it determines how much oxygen is required for biological combustion to be completed. where as direct measures the amount of heat produced from metabolism.
explanation of indirect calorimetry..
when converting the amount of oxygen consumed it is important to identify which energy substrate is being metabolised.
energy made when fat is the only substrate being oxidised is 19.7kj or 4.7 kcal per liter of oxygen used.
energy made when carbohydrate is the only substrate being oxidised is 21.1kj or 5.05kcal per liter of oxygen used.
it is often estimated that the energy expenditure of exercise is using 5kcal or 21kj per liter of oxygen used.
with indirect calorimetry the individual is equired to inhale ambient air composed of 20.93% oxygen, 0.03% carbon dioxide, 79.04% nitrogen.
so the VO2 is determined by the change of the volume of oxygen that is exhaled to the volume of oxygen which is inhaled. Aerobic exercise:
During aerobic work, 50-60% of the energy comes from fats
Primarily carbohydrates are used during the first several minutes of exercise
For an average fit person, it takes 20 to 30 minutes of continuous aerobic activity to burn 50% fat and 50% carbohydrate
There is approximately a 7 fold increase of fat mobilization after 1 hour of exercise
Proteins contribute less than 2% of the substrates used during exercise of less than 1 hour.
It is known that the energy needs for sustaining maximal exercise of very short duration are largely met by the creatine phosphate breakdown such that its concentration decreases to almost zero at the end of maximal exercise leading to exhaustion. An almost complete creatine phosphate recovery is normally observed within rest periods lasting about 4 minutes following repeated maximal exercises of short duration
At rest, 33-42%% of the body's energy comes from carbohydrates, or glycogen, stored within the muscles and liver. 41-67% comes from fat. (Kang, 2012) Carbohydrate feeding during exercise An individual exercising longer than 60 mins will benefit from carbohydrate feeding during exercise because prolonged exercise depletes muscle glycogen stores. low levels of muscle glycogen and blood glucose will lead to fatigue.
consuming about 60g of liquid or solid carbohydrates every hour has been shown to reduce fatigue in prolonged exercise.
this has been demonstrated when the intensity of exercise passes 70% vo2 max because there is a higher demand on carbohydrate breakdown.
carbohydrate feeding can improve endurance performance by...
- maintaining blood glucose and high levels of carbohydrate oxidation
- sparing liver and muscle glycogen
- enhancing the function od the central nervous system
its shown that the timing of when the carbohydrate is consumed has little effect on the use of the ingested carbohydrate, which is normally measured by determining exogenous carbohydrate oxidation rates.
in theory the optimal of carbohydrate which should be consumed should be the amount which results in the maximal exogenous carbohydrate oxidation rate
a large study from Jeukendrup and jentjens (2000) found that consuming 1.1-1.2g of carbohydrate per minute produce the maximal exogenous carbohydrate oxidation rate
these findings suggest that atheletes who ingest 70g of carbohydrates per hour can expect optimal carbohydrate delivery.
this can be found in...
- 1 liter of sports drink
- 600ml of coke
- 1.5 energy bars
- 3 medium bananas Free fatty acid liberation and mobilisation By far the largest energy reserve in the human body is adipose tissue triglycerides, these reserves are an important source of fuel during prolonged endurance exercise.
most lean adults can store 80,000 kcal of potential energy stored as fat in adipose tissue.
this must first be hydrolyzed for the fatty acids delivered to the working muscles for it to be oxidised.
using this energy source delay the onset of glycogen depletion and hypoglycemia.
use of adipose tissue triglycerides as a fuel during exercise requires the coordinated regulation of lipolysis, blood ﬂow and fatty acid transport in skeletal muscle to enhance the delivery of released fatty acids from adipose tissue to the mitochondria of working muscle. Effect of elevated blood glucose and plasma insulin levels After eating a meal the monosaccharidses are absorbed and travel to the liver along the hepatic portal vein. when it reaches the liver much of the fructose and galactose is then metabolised for energy.
If glucose is needed in a tissue wit will be transported in the blood, the amount of glucose that is regulated in the blood at about 70-100mg per 100 ml of blood. This level of glucose in the blood is important for brain cells and red blood cells.
when blood glucose levels rise to high there is an increase in insulin secreted from teh pancreas. this causes the liver cells to link with the excess glucose resulting in branched chains of glycogen.
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