Athletics and Nutrition

Basic goal of sports nutrition Ensure adequate fuel and fluid Preferred fuel depends on the intensity and duration of the physical activity. Fuel sources Fat and Carbohydrate

Fuel Sources Low intensity Fat is the primary source Ex. Walking High intensity Carbohydrate is the primary source During prolonged exercise, fat becomes an important fuel source.

Energy Sources *ATP* Phosphocreatine CHO – Glucose/Glycogen in glycolysis and TCA FA Oxidation Protein – Amino Acid Catabolism

Phosphocreatine Quick source for ATP in the muscle. When ADP accumulates - Phosphocreatine from muscle cells donate a P to produce Creatine and ATP. Creatine is converted to creatinine and excreted in the urine. Only in short intense exercise < 30 sec

Anaerobic Glycolysis

Oxygen limiting during exercise Faster Reduce pyruvate to lactate via lactate dehydrogenase to produce ATP Net Production: 2 ATP 2 Lactate Provides energy for 1-3 minutes For shorter events (sprint, weight lifting)

Fates of Lactate Lactate (lactic acid) is acidic thus must be removed from the blood. Impairs breakdown of glc and inhibits calcium binding for muscle contraction Convert back to pyruvate Cori Cycle

Aerobic Glycolysis Oxygen based systems Used for long term exercises that require longer endurance Can produce a tremendous amount of ATP Can extract energy from fat Supplies energy more slowly Lung -> blood -> muscle cells -> mitochondria

Anaerobic vs. Aerobic Anaerobic and aerobic energy systems work together to fuel athletes Most activities use ATP from both anaerobic and aerobic Short burst exercise – completely anaerobic (sprint) Marathon – completely aerobic Tennis, Basketball, Soccer, Swimming, 2 mile run Both Anaerobic and Aerobic

Muscle Fiber Types Type I Slow twitch – slow speed of contraction Primarily use aerobic metabolism Athletes with more type I have higher blood lactate threshold Facilitate long duration activities Type II Fast twitch – fast speed of contraction Anaerobic metabolism Type IIa – aerobic and anaerobic Type IIb – fastest and most glycolytic fiber type.

Muscle Fiber Most activities require both fast and slow twitch Activities that require more Type II Deplete glycogen stores faster Ratio of slow to fast twitch depends on genetic predisposition 45% to 55% of people’s muscle fibers are slow twitch. Marathon runners can have up to 90% to 95% slow twitch muscle fibers.

Respiratory Quotient (RQ) RQ measures what type of fuel is being burned. Glycogen or Fat? Amount of CO 2 Produced RQ = Amount of O 2 Consumed

RQ RQ for certain nutrients: Carbohydrate: 1.0 Protein: 0.8 Fat: 0.7

How to calculate RQ Oxidation of glucose (C 6 H 12 O 6 ) C 6 H 12 O 6 + O 2 CO 2 + H 2 O Nutrient + O 2 CO 2 + H 2 O C 6 H 12 O O 2 6 CO H 2 O RQ = (6 CO 2 )/( 6 O 2 ) = 1.0

RER Respiratory Exchange Ratio (RER) Amount of CO 2 Expired RER = Amount of O 2 Consumed

RER Assumptions are valid for resting, steady state Can exceed 1.0 during heavy non-steady state. Hyperventilation Carbon dioxide output increases during hyperventilation Not attributable to foodstuff oxidation

How to measure RER? Measured by gases exchanged at the mouth Indirect calorimetry Open circuit Closed circuit

RER Assumption: exercising and consuming 2.0 L of O2 per min Gas analysis: RER = 0.85 Expending 9.72 kcal/min (2.0 L of O2 per min X 4.86 kcal/O2) Thus if exercising for 30 min then burning 292 kcal.

Michael Phelps’ Diet

Phelps’ Diet

Diet 60% Carbohydrate (Can be 70% for extreme exercise) Less than 30% fat About 15% protein

Carbohydrate Athletes depend on glycogen stores for energy Two types of glycogen in the body Muscle glycogen Immediate energy for muscle during exercise Muscles lack glucose phosphatase to remove PO4 from glucose. Hitting the wall Liver glycogen Fuels muscle and brain At rest, brain and CNS use most of the glucose Bonking/Crashing

Glycogen Depletion At the beginning of a race, the body uses muscle glycogen rapidly However as the race progresses, the body begins to use the glycogen much slower. After 3 hours, glycogen stores become depleted and the athlete experiences muscle weakness and confusion. As exercise intensity and duration increases, glycogen depletion is accelerated. Ex. Sprinting uses muscle glycogen about 30 to 40 times faster than walking.

Glycogen Depletion

Carbohydrate Guidelines for athletes recommend a high CHO diet during training (minimum of 60% of total calories) Helps to increase glycogen stores and increase endurance. Can prevent mental and physical fatigue. CHO should be mainly complex CHO Added sugars (simple) should be minimized

Complex CHO Polysaccharides Slower absorption rate Does not induce a strong insulin response Help to maximize glycogen stores

Complex CHO

Glycemic Index Ranking of food based on response to blood glucose level Area under the curve (AUC) of blood glucose level after ingestion of test food divided by the AUC of a reference food (glucose or white bread) Reflects rate of digestion and absorption of CHO-rich food CHO that break down quickly and release glucose into the bloodstream rapidly have high glycemic index. Low glycemic index = slower digestion Glycemic index scale is culture dependent

Glycemic Index Influenced by Food form (particle size, texture, viscosity) Degree of food processing and cooking Presence of fructose or lactose Ratio of amylopectin and amylose in starch

Glycemic Index

Carbohydrate Loading Carbo Loading Used in endurance athletes to maximize glycogen stores Recommended for activities lasting longer than 60 to 90 minutes Longer carbo loading days before event, longer exercise duration. Choice of carb: low glycemic index Fruits, vegetables, whole wheat pasta and grains Women respond different than men Glycogen storage more efficient 2 weeks before menstruation

Problems with Carbo Loading Which CHO to consume? Too much CHO can increase fat storage Depending on person, body can respond differently Decrease in protein and fat consumption Water? 3 grams of water is need to store 1 gram of glycogen

Carbohydrate Intake before exercise 2 to 4 hours before exercise to replenish glycogen stores. Athletes with GI distress should consume less CHO Intake during exercise Drink fluids with low to moderate amount of simple CHO. Plain water is adequate for short events (< 1 hr) Consuming CHO before and after is more beneficial Intake after exercise Can take up to 1 or 2 days to replenish glycogen stores. Intake of CHO after an intense exercise is critical. Replenish glycogen stores quickly Prevent protein breakdown and enhance protein retention. Simple sugars, glucose, and sucrose effectively replenish glycogen, but not fructose.

Recovery Need to replete glycogen stores Consume high glycemic index CHO CHO important to avoid further muscle catabolism Need protein as well to prevent wear and tear of muscles (rebuilding muscles) Adequate sleep and rest