Year 10 Sports Physiology - Energy for Physical Activity Study Guide

Food Fuels

• Energy Requirements: The human body requires energy for all basic functions (involuntary movements like breathing and blinking) and for chosen physical activities (walking to soccer). Energy creates muscular contractions to move the skeleton.

• Adenosine Triphosphate (ATP): The chemical compound used to create energy for muscular movement. All food and liquids contains nutrients for growth, repair, and energy creation. ATP is produced via dietary intake through three essential food fuels: Carbohydrates, Fats, and Proteins.

• Carbohydrates (CHO):

  • Sources: Sugars, fruit, vegetables, cereals, and grain products (bread, pasta).

  • Process: Digested into $glucose$ (small molecule) for blood transport; stored as $glycogen$ (complex molecule) in muscles and liver.

  • Preference: Preferred fuel for activity due to easy access (stored in muscle cells), plentiful supply, and ability to be utilized in both aerobic and anaerobic conditions.

  • Efficiency: It is more economical than fats because it requires approximately $50\%$ less oxygen to break down for ATP production.

  • Yield: Aerobic system produces approximately $38$ molecules of ATP per glucose molecule; anaerobic glycolysis system produces approximately $2$ molecules.

  • Excess: Converted to fat and stored as adipose tissue.

• Glycaemic Index (GI): A scale measuring the rate of carbohydrate breakdown and its effect on blood glucose. Glucose is the reference value at $100$.

  • Low GI (<55): Slowly digested and absorbed; releases energy over a long period. Useful for endurance activities. Examples: Porridge, lentils, whole grain bread, low-fat yoghurt.

  • Moderate GI ($55-70$): Examples: Basmati rice, muffins, pancakes, boiled potato, chocolate, sultanas.

  • High GI ($70-100$): Breaks down/releases energy quickly. Useful during endurance events (gels/fluids) and post-exercise recovery. Examples: Sports drinks, watermelon, white bread, baked potato, honey.

• Fats (Lipids):

  • Sources: Dairy, oils, nuts, meats.

  • Process: Digested into free fatty acids (transport) and stored as adipose tissue or as triglycerides in the muscle.

  • Usage: Major fuel for long-term, sub-maximal activity and at rest.

  • Condition: Can only be utilized under aerobic conditions.

  • Yield: Very high yield; approximately $460$ molecules of ATP from one triglyceride molecule.

• Proteins:

  • Process: Stored as muscle tissue and amino acids.

  • Usage: Rarely used for ATP. Utilized only in extreme circumstances (starvation, ultra-marathons) when carbohydrate and fat stores are depleted.

  • Efficiency: Requires very high oxygen amounts and results in very low ATP yield.

Summary Table of Food Fuels

• Carbohydrate ($55-60\%$ of diet):

  • Storage: Glycogen in muscle and liver.

  • Systems: Aerobic and Anaerobic Glycolysis.

  • Transport: Glucose.

  • Yield: Aerobic ($38\,mol$), Anaerobic ($2\,mol$).

  • Reaction Length: Aerobic (medium), Anaerobic Glycolysis (short).

• Fats ($25-30\%$ of diet):

  • Storage: Triglycerides in muscle, adipose tissue.

  • Systems: Aerobic.

  • Transport: Free fatty acids and glycerol.

  • Yield: High ($460\,mol$).

  • Reaction Length: Long.

• Protein ($10-15\%$ of diet):

  • Storage: Muscle tissue.

  • Systems: Aerobic.

  • Transport: Amino acids.

  • Yield: Very low.

Summary of Fuel Usage by Intensity

• At Rest:

  • Carbohydrates: $33\%$

  • Fats: $67\%$

  • Proteins: $0\%$

• Prolonged Sub-maximal Activity:

  • Carbohydrates: $80\%$

  • Fats: $15\%$

  • Proteins: $5\%$

• Maximal Intensity:

  • Carbohydrates: $100\%$

  • Fats: $0\%$

  • Proteins: $0\%$

Chemical Fuels

• Phosphocreatine (PC or CP): Not derived directly from the diet in the context of food fuels. Stored in muscles in very small amounts.

• Usage: Utilized under anaerobic conditions for maximal intensity activity of very short duration (less than $10$ seconds).

• Yield: Very low yield (less than $1\,mol$ of ATP).

• Reaction: Very short and fast chemical reaction.

Characteristics of Energy Systems

• ATP-PC System (Alactacid / Phosphagen System):

  • Fuel: Phosphocreatine (PC).

  • Intensity: Maximal ($95-100\%$ max HR).

  • Duration: Dominance ($1-5$ seconds), Peak Power ($2-4$ seconds), total duration up to $10$ seconds.

  • Rate: Explosive (very rapid).

  • Yield: Low ($0.7-1\,molecule$).

  • By-products: Inorganic phosphates and ADP.

  • Recovery: Passive. $70\%$ replenishment in $30$ seconds; $98\%$ in $3$ minutes; $100\%$ in $10$ minutes.

  • Fitness Components: Speed, anaerobic capacity, muscular strength, power, and agility.

• Anaerobic Glycolysis System (Lactacid System):

  • Fuel: Glycogen.

  • Intensity: High intensity ($85-95\%$ max HR).

  • Duration: Dominance ($5-60$ seconds), Peak Power ($5-15$ seconds).

  • Rate: Fast (slower than ATP-PC due to complex reactions).

  • Yield: Low ($2\,molecules$).

  • By-products: Lactic Acid (Lactate and $H^+$ ions), ADP.

  • Fatigue: Caused by accumulation of $H^+$ ions creating an acidic environment that inhibits glycolytic enzymes and slows glycogen breakdown.

  • Recovery: Active (to remove $H^+$ ions).

  • Fitness Components: Anaerobic capacity, speed, muscular power (repeated), strength, muscular endurance.

• Aerobic System (Oxygen System):

  • Fuel: Carbohydrates (all intensities except rest), Fats (rest, glycogen sparing, or depletion), Proteins (extreme depletion).

  • Intensity: Sub-maximal (<85\% max HR) or rest.

  • Duration: Dominant after $75$ seconds (peak power at $60-90$ seconds).

  • Rate: Medium (slowest due to complexity; slower when using fats).

  • Yield: High ($38$ ATP per glucose, $460$ ATP per triglyceride).

  • By-products: Carbon dioxide ($CO_2$), water ($H_2O$), and heat.

  • Recovery: Active and dietary.

  • Fitness Components: Aerobic capacity, local muscular endurance.

Interplay of Energy Systems

• Simultaneous Function: All energy systems function at all times. No system operates in isolation.

• Predominance: Determined by intensity and duration. For example, in basketball, a player jumping for a rebound uses the ATP-PC system if stores are full. If PC is depleted, anaerobic glycolysis provides "extra" energy, though it might not be the overall predominant system.

• Switching Fuels: In marathons, athletes may "hit the wall." This occurs after approximately $2-3$ hours when carbohydrate stores are depleted and the body switches to fats as the major fuel source, resulting in a slower rate of ATP production and fatigue.

• VO2 Max: When an athlete works above $100\%$ of their VO2 Max (maximum aerobic power), the additional energy is supplied by anaerobic glycolysis.

Fatigue and By-products

• Hydrogen ($H^+$) Ions: Produced during anaerobic glycolysis. Increases muscle acidity, slowing glycogen breakdown and inhibiting the coupling of myosin cross bridges with actin filaments, reducing contraction force.

• Lactate Inflection Point (LIP): The point during exercise where lactate production equals removal. If intensity increases beyond LIP, $H^+$ ions increase exponentially.

• Inorganic Phosphates ($P_i$): Accumulated as ATP breaks down to ADP. High levels decrease ATP availability, decrease calcium release, and slow neural transmission.

• Aerobic By-products: Heat, water, and $CO_2$ are not fatigue-causing and are removed via sweating and breathing.

Recovery Methods

• Active Recovery: Low intensity (<40\% max HR) using the same muscle groups. Maintains higher oxygen levels to metabolise lactate/$H^+$ ions. Creates a "muscle pump" to prevent venous pooling.

• Passive Recovery: Essential for PC replenishment ($3$ mins for $98\%$). Massage can assist by creates an artificial muscle pump.

• Contrast Therapy (Shunting): Alternating hot/cold showers to cause vasodilation and vasoconstriction, flushing blood to transport oxygen and remove by-products.

• Dietary Recovery: Consume High GI foods within the first $30$ minutes post-exercise for rapid glycogen replenishment. A delay of one hour can require an additional $24$ hours to replenish stores.

Lab Report: Fitness Centre Observation

• Activity 1: Bench Press (5 reps heavy load): Duration <10\,sec, Maximal intensity. Dominant system: ATP-PC. Fuel: PC.

• Activity 2: Sprint (15 sec): Duration $10-15\,sec$, Maximal intensity. Dominant system: Anaerobic Glycolysis. Fuel: Carbohydrates.

• Activity 3: Rowing (3 min): Duration $2-4\,min$, High/Moderate intensity. Dominant system: Aerobic. Fuel: Carbohydrates.

• Activity 4: Stationary Bike (10 min): Duration $10+\,min$, Sub-maximal intensity. Dominant system: Aerobic. Fuel: Fats + Carbohydrates.

Team Sport Example: Netball

• Intermittent Nature: Combines explosive actions and periods of low intensity.

• ATP-PC Movements: Sprinting for intercept, jumping for rebound (<10\,sec).

• Anaerobic Glycolysis Movements: Fast attacking play, chasing opponents ($10-60\,sec$).

• Aerobic Movements: Jogging into position, quarter recovery, walking back to center (>2\,min).

Case Study Examples

• AFL (Buddy Franklin - Full Forward): Primarily relies on ATP-PC for leads/marks. If several leads occur in succession with no break, anaerobic glycolysis takes over. Uses aerobic system while rest in the forward line.

• AFL (Patrick Dangerfield - Midfielder): Relies on the aerobic system to cover ground. Anaerobic glycolysis handles continuous high-intensity bursts. ATP-PC handles explosive kicks or shots.

• Beijing 2008 Long Jump (Irving Saladino): Jump takes roughly $2-4$ seconds. Relies purely on ATP-PC. Because jumpers have roughly $3$ minutes between attempts, PC stores are almost entirely ($98\%$–$100\%$) replenished, allowing maximal performance each jump.

• Beijing 2008 Women's Marathon (Constantina Dita-Tomescu): Duration $2\,hrs\,26\,mins$. Predominant system: Aerobic. Major fatigue causes: Glycogen depletion and dehydration.

• London 2012 400m (Kirani James): Time $43.94\,sec$. Predominant system: Anaerobic glycolysis. Start and acceleration: ATP-PC. Crosses line: Aerobic system (after $30$ seconds of activity, aerobic system contributes more than half of ATP).