Carbs- The basics Glucose is a type of monosaccharide that is in the food that we consume Blood glucose is used to fuel the working muscles Called glycogen when stored in muscles or the liver
What happened to your breakfast?? Carbohydrate meal is eaten and digested, Blood glucose levels rise, and the pancreas secretes insulin GLYCOGENESIS- glucose converted to glycogen [for ST storage] as long as both insulin and glucose remain plentiful Blood glucose used for immediate energy requirements When glucose levels begin to fall, insulin secretion is reduced, and glycogen synthesis stops. About four hours after a meal glycogen begins to be broken down to be converted again to glucose [GLYCOGENOLYSIS] For the next 8–12 hours, glucose derived from liver glycogen will be the primary source of blood glucose to be used by the rest of the body for fuel.
Carbs terminology Glycogenesis = glucose glycogen Glycogenolysis = glycogen glucose Gluconeogenesis=non CHO sources glucose Glycolysis = Glucose Pyruvic acid Krebs cycle 4 calories of Energy (+ Co2 and H20) 1 gram glucose (+ oxygen)
Storage LIVER- Only the glycogen stored in the liver can be made accessible to other organs. 100–120 g stored in an adult MUSCLES- lower concentration (1% of the muscle mass), but the total amount exceeds that in liver. Small amounts of glycogen are found in the kidneys, and even smaller amounts in certain glial cells in the brain and white blood cells Once muscle glycogen stores are depleted performance decreases
Glycaemic Index Index for comparing the blood glucose response from the ingestion of different foods. - The more complex the carbohydrate, and the more fat, protein and fibre in the food lower glycaemic index. High = GI>70 Mod = GI 56-70 Low = GI<55 Lower = slower
Whole wheat pasta Glucose White breadIngestion Note the differences in the area under the curve Note that the blood glucose response to white bread is the standard reference
Major Considerations RDI’s - CHO & protein requirements Pre competition meals Fluid replacement
Daily intake Normal people 1500—2500 calories Athletes 1400 (gymnasts) – 6000 (TDF cyclists) Carbohydrate= 55-60% Fats <35% Protein= 10-15%
RDI’s- Protein Sedentary people and recreational athletes have similar protein requirements –Sedentary Adults: 0.8 to 1 gram of protein p/kg BM. –Athletes: 1.2-1.8 g protein p/kg BM 87 kg x 1.8 g or 87 kg x 1.2g = 104.4 - 156.6 g p/day 8 28.5 x 26 x 232 x 2
RDI’s- Carbs Depends on sport –Normal people: 5 g/kg –Athletes: 5-13 g /kg depending on training intensity 59 kg x 8 g = 472 g p/day 20 465 40 75 1710 2085 20 4580
Preparation for Competition- Carb loading In general –Taper exercise, 50% CHO diet 1 st 3 days –V. low exercise, 80% CHO diet 3 days prior Strict protocol –Depletion Day 1- Exhaustive exercise Day 2,3,4 mod intensity training & low carb intake (100g p/day) Day 5,6,7 High CHO intake (400-700g)
Day of Competition Nutrition 1-4 hours before= Large CHO meal –200-500 calories –150 – 300g carbohydrate (3-5g CHO p/kg BW) OR 4 hours before – meal (200 g CHO) 1 hour before- snack (100g CHO)
Rebound hypoglycaemia High GI carbohydrate consumed 15-45 min before exercise it can stimulates insulin secretion converts glucose to glycogen and stores it low blood glucose levels Less fuel available for exercise Pg 333 of text
Liquid Carbohydrate Ingestion Suited for long duration (> 60 min) exercise where a glucose source is needed to support blood glucose As long as it is consumed late in exercise when muscle glycogen stores are low it will not cause rebound hypoglycaemia Need at least 45 g/CHO/Hr During hot and humid conditions, a lower [CHO] drink would allow greater volumes to be ingested. CHO should be mostly glucose
CHO ingestion every 20 min CHO ingestion late in exercise No CHO ingestion 65-75% VO2max
Post Competition Depends on time and intensity –after low intensity exercise - 7-9 mmol/kg/Hr –after high intensity exercise - ~ 15 mmol/kg/Hr Important to consume 2 hours post exercise while rate of glycogen synthesis is high Large carbohydrate rich meal With some addition protein Rest Rehydrate
Liquids - Rehydration Sweat rates increase with intensity of exercise Fit people sweat more and sooner; and it is more dilute Can be up to 1- 2.8 L/hr –Sodium (Na), Potassium (K), Magnesium (Mg), Chlorine (Cl) Loss of body weight > 3% = danger Consume 500-1000 ml per hour
Fluids- 2 hours before: –400-600 ml fluid During –150-350 ml every 15-20 minutes –If > 1 hour- 4-8% CHO plus Na and Cl After –Continue H2o consumption- thirst not an accurate indicator –900-1200 ml for every kg lost –Caffeine, energy drinks and alcohol further dehydrate Recommendations from text box in page 347
Gastric emptying Maximal rates of 1-1.2 L /hr with gastric volumes of 100 - 200 mL.
Nutrient and electrolyte content of commercial drinks.
Important nutrients & fads Female Athlete Triad Steroid use/abuse Over-consumption proteins Muscle building powders Creatine
Summary Sports nutrition has a huge impact on performance Nutrition and rehydration account for huge gains Need to be careful of rebound hypoglycaemia and gastric emptying Expensive pills, potions and fads account for minute gains if any at all
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