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HMS, BM 2013 HSC 18 MC

What is a common feature of both the alactacid (ATP-PCr) and lactic acid energy systems?

  1. Lactic acid is produced.
  2. ATP is resynthesised anaerobically.
  3. Both systems take the same period of time to recover.
  4. The accumulation of lactic acid in the working muscles causes fatigue.
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\(B\)

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NOTE: This question has been updated to include the HMS system naming of the alactacid system with ATP-PCr.

  • B is correct: Both alactacid (ATP-PCr) and lactic acid systems operate without oxygen.

Other Options:

  • A is incorrect: Only lactic acid system produces lactic acid.
  • C is incorrect: Systems have different recovery time periods significantly.
  • D is incorrect: Only lactic acid system causes fatigue through accumulation.

♦♦ Mean mark 52%.

HMS, BM 2018 HSC 18 MC

The graph shows the percentage of energy produced in a variety of activities
 

Based on the graph, which of the following statements is the most accurate?

  1. After two seconds no more ATP is created.
  2. Stored energy plays a very small role in a vertical leap test.
  3. The lactic acid system is the major source of energy at the end of a 100-metre sprint.
  4. Aerobic energy is the major source of energy from the 10-second mark in a 400-metre sprint.
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\(C\)

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  • C is correct: 100-metre sprint duration matches timeframe where lactic acid system dominates energy production.

Other Options:

  • A is incorrect: ATP continues to be produced by different systems after two seconds.
  • B is incorrect: Stored ATP plays a major role in explosive movements like vertical leaps.
  • D is incorrect: 400-metre sprint relies heavily on anaerobic systems, not primarily aerobic energy.

♦♦ Mean mark 45%.

HMS, BM EQ-Bank 301 MC

A sports scientist is designing interval training programs targeting different energy systems. Which combination of intensity, work interval and recovery period would MOST effectively develop the glycolytic energy system?

  1. 95-100% maximum effort, 5-10 second work intervals, 3-5 minute recovery periods
  2. 75-85% maximum effort, 3-5 minute work intervals, 1-2 minute recovery periods
  3. 85-95% maximum effort, 30-90 second work intervals, 1-3 minute recovery periods
  4. 60-75% maximum effort, 10-20 minute work intervals, 2-3 minute recovery periods
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\(C\)

Show Worked Solution
  • C is correct:
    • The glycolytic (lactic acid) system is optimally trained using 85-95% intensity with 30-90 second work intervals and 1-3 minute recovery periods.
    • This creates the optimal stimulus for lactate production and clearance adaptations.

Other Options:

  • A is incorrect: 5-10 second intervals with long recovery primarily target the ATP-PCr system, not the glycolytic system.
  • B is incorrect: 3-5 minute work intervals with shorter recovery shifts training toward the aerobic system rather than focusing on glycolytic development.
  • D is incorrect: 60-75% intensity with 10-20 minute intervals represents aerobic endurance training that won’t effectively develop the glycolytic system.

HMS, BM EQ-Bank 208 MC

A rower is competing in a 2000 m race lasting 6-8 minutes. What is the predominant energy system used?

  1. ATP-PCr only
  2. Lactic acid only
  3. Aerobic only
  4. Combination of lactic acid and aerobic
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\(D\)

Show Worked Solution
  • D is correct: Duration requires both systems working together

Other Options:

  • A is incorrect: Duration too long
  • B is incorrect: Cannot sustain effort
  • C is incorrect: Intensity too high for aerobic only

HMS, BM EQ-Bank 184

Analyse how the three energy systems interact to provide energy during a 1500 metre race.   (8 marks)

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Sample Answer

  • As the race begins, the ATP-PCr system provides immediate energy for the explosive start and initial acceleration to race pace within the first 10 seconds.
  • The lactic acid system then becomes increasingly important during the first 400 metres as runners establish position and settle into race pace, contributing approximately 15% of energy requirements.
  • The aerobic system becomes the dominant energy provider after the first lap, delivering approximately 85% of energy needs for the remainder of the race through oxidative phosphorylation.
  • During tactical surges or when overtaking competitors, there is increased contribution from the lactic acid system while the aerobic system continues to operate.
  • Brief reductions in pace allow partial replenishment of ATP-PCr stores which can then be utilised for short bursts of acceleration when responding to competitors’ moves.
  • Accumulated lactic acid from anaerobic glycolysis may begin to impact performance in the final stages of the race if the pace has been too aggressive.
  • The aerobic system’s efficiency in providing energy while clearing metabolic waste products becomes crucial in maintaining race pace through the middle stages.
  • Throughout the race, all three energy systems operate simultaneously with their relative contributions shifting based on pace changes and tactical demands of the race.
Show Worked Solution

Sample Answer

  • As the race begins, the ATP-PCr system provides immediate energy for the explosive start and initial acceleration to race pace within the first 10 seconds.
  • The lactic acid system then becomes increasingly important during the first 400 metres as runners establish position and settle into race pace, contributing approximately 15% of energy requirements.
  • The aerobic system becomes the dominant energy provider after the first lap, delivering approximately 85% of energy needs for the remainder of the race through oxidative phosphorylation.
  • During tactical surges or when overtaking competitors, there is increased contribution from the lactic acid system while the aerobic system continues to operate.
  • Brief reductions in pace allow partial replenishment of ATP-PCr stores which can then be utilised for short bursts of acceleration when responding to competitors’ moves.
  • Accumulated lactic acid from anaerobic glycolysis may begin to impact performance in the final stages of the race if the pace has been too aggressive.
  • The aerobic system’s efficiency in providing energy while clearing metabolic waste products becomes crucial in maintaining race pace through the middle stages.
  • Throughout the race, all three energy systems operate simultaneously with their relative contributions shifting based on pace changes and tactical demands of the race.

HMS, BM EQ-Bank 183

Describe the interplay of energy systems during a 90-minute soccer match.   (6 marks)

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Sample Answer

  • The aerobic system provides most of the total energy throughout the match, sustaining jogging, positioning, and recovery between high-intensity efforts.
  • ATP-PCr system activates for explosive movements that occur regularly throughout the game.
  • These include sprints to beat defenders, jumping for headers, and rapid direction changes lasting 5-10 seconds.
  • The glycolytic system engages during extended high-intensity sequences such as overlapping runs, chasing opponents and consecutive sprints lasting 30-60 seconds.
  • This accumulates lactic acid, causing temporary fatigue until recovery occurs.
  • All three systems operate simultaneously with constantly shifting contributions based on immediate demands.
  • A midfielder transitions from aerobic jogging to ATP-PCr sprinting to intense defensive work within seconds.
  • Natural breaks allow partial energy system recovery during throw-ins, free kicks and tactical pauses.
  • These brief rests permit some phosphocreatine replenishment for the next explosive effort.
  • Energy system contributions vary by position, with central midfielders using more aerobic energy while wingers need more ATP-PCr for repeated sprints.
  • Fatigue increasingly affects system interplay as matches continue, with accumulated lactic acid and glycogen use reducing high-intensity actions in final stages.
  • Substitutions strategically introduce fresh energy systems when starters show declining performance.
Show Worked Solution

Sample Answer

  • The aerobic system provides most of the total energy throughout the match, sustaining jogging, positioning, and recovery between high-intensity efforts.
  • ATP-PCr system activates for explosive movements that occur regularly throughout the game.
  • These include sprints to beat defenders, jumping for headers, and rapid direction changes lasting 5-10 seconds.
  • The glycolytic system engages during extended high-intensity sequences such as overlapping runs, chasing opponents and consecutive sprints lasting 30-60 seconds.
  • This accumulates lactic acid, causing temporary fatigue until recovery occurs.
  • All three systems operate simultaneously with constantly shifting contributions based on immediate demands.
  • A midfielder transitions from aerobic jogging to ATP-PCr sprinting to intense defensive work within seconds.
  • Natural breaks allow partial energy system recovery during throw-ins, free kicks and tactical pauses.
  • These brief rests permit some phosphocreatine replenishment for the next explosive effort.
  • Energy system contributions vary by position, with central midfielders using more aerobic energy while wingers need more ATP-PCr for repeated sprints.
  • Fatigue increasingly affects system interplay as matches continue, with accumulated lactic acid and glycogen use reducing high-intensity actions in final stages.
  • Substitutions strategically introduce fresh energy systems when starters show declining performance.

HMS, BM EQ-Bank 182

Describe how the three energy systems interact during a 3-minute boxing round.   (5 marks)

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Sample Answer

  • The ATP-PCr system activates instantly for explosive combinations and power punches. It provides maximum force for 10-15 seconds before depletion occurs. 
  • Sustained exchanges beyond 10 seconds shift dominance to the glycolytic system. This maintains high-intensity output for combinations lasting up to 60 seconds.
  • The aerobic system operates continuously throughout the round at varying intensities. It provides baseline energy during footwork and defensive movements.
  • All three systems function simultaneously rather than sequentially during combat. Their relative contributions fluctuate based on fighting intensity and duration.
  • Brief pauses between exchanges allow partial PCr replenishment within 20-30 seconds. This enables repeated explosive efforts throughout the round.
  • Lactic acid progressively accumulates from repeated high-intensity combinations. This causes fatigue and reduced punching power in the round’s final minute.
  • Skilled boxers manage intensity fluctuations to optimise energy system contributions. They alternate between explosive attacks and active recovery movements.
Show Worked Solution

Sample Answer

  • The ATP-PCr system activates instantly for explosive combinations and power punches. It provides maximum force for 10-15 seconds before depletion occurs. 
  • Sustained exchanges beyond 10 seconds shift dominance to the glycolytic system. This maintains high-intensity output for combinations lasting up to 60 seconds.
  • The aerobic system operates continuously throughout the round at varying intensities. It provides baseline energy during footwork and defensive movements.
  • All three systems function simultaneously rather than sequentially during combat. Their relative contributions fluctuate based on fighting intensity and duration.
  • Brief pauses between exchanges allow partial PCr replenishment within 20-30 seconds. This enables repeated explosive efforts throughout the round.
  • Lactic acid progressively accumulates from repeated high-intensity combinations. This causes fatigue and reduced punching power in the round’s final minute.
  • Skilled boxers manage intensity fluctuations to optimise energy system contributions. They alternate between explosive attacks and active recovery movements.

HMS, BM EQ-Bank 181

Explain how the lactic acid system contributes to energy production during a 200 m sprint.   (4 marks)

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Sample Answer

  • During the 200 m sprint, glucose is broken down without oxygen through glycolysis to produce ATP for sustained high-intensity muscle contractions.
  • This anaerobic process creates lactic acid as a by-product which accumulates in the working muscles causing fatigue.
  • The lactic acid system can maintain high-intensity performance for up to 60-90 seconds before waste products significantly impair muscle function.
  • As a 200 m sprint typically takes 20-25 seconds, this system provides the majority of energy required after the initial ATP-PCr stores are depleted at around 10 seconds.
Show Worked Solution

Sample Answer

  • During the 200 m sprint, glucose is broken down without oxygen through glycolysis to produce ATP for sustained high-intensity muscle contractions.
  • This anaerobic process creates lactic acid as a by-product which accumulates in the working muscles causing fatigue.
  • The lactic acid system can maintain high-intensity performance for up to 60-90 seconds before waste products significantly impair muscle function.
  • As a 200 m sprint typically takes 20-25 seconds, this system provides the majority of energy required after the initial ATP-PCr stores are depleted at around 10 seconds.

HMS, BM EQ-Bank 180

Outline how the ATP-PCr system provides energy for immediate muscle contraction.   (3 marks)

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Sample Answer

  • Muscle contraction begins when stored ATP splits into ADP and inorganic phosphate, releasing immediate energy for movement.
  • Phosphocreatine (PCr) rapidly breaks down, donating its phosphate group to ADP, regenerating ATP within milliseconds.
  • This phosphate transfer continues without oxygen requirement, sustaining maximal effort for 10-15 seconds until PCr depletes.
  • The system’s speed results from PCr stores being located directly in muscle cells, eliminating transport time and enabling explosive movements.
Show Worked Solution

Sample Answer

  • Muscle contraction begins when stored ATP splits into ADP and inorganic phosphate, releasing immediate energy for movement.
  • Phosphocreatine (PCr) rapidly breaks down, donating its phosphate group to ADP, regenerating ATP within milliseconds.
  • This phosphate transfer continues without oxygen requirement, sustaining maximal effort for 10-15 seconds until PCr depletes.
  • The system’s speed results from PCr stores being located directly in muscle cells, eliminating transport time and enabling explosive movements.

HMS, BM EQ-Bank 179 MC

During a 400 metre sprint race, an athlete's performance is most dependent on which combination of energy systems?

  1. ATP-PCr and Aerobic
  2. Glycolytic and ATP-PCr
  3. Aerobic and Glycolytic
  4. Equal contribution from all three systems
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\(B\)

Show Worked Solution
  • B is correct: A 400 m sprint typically takes 45-60 seconds requiring both immediate energy from ATP-PCr for the explosive start and lactic acid system for maintaining the high-intensity effort throughout the race.

Other Options:

  • A is incorrect: Aerobic contribution is minimal during high-intensity 400m sprints
  • C is incorrect: Aerobic system isn’t significantly involved at this intensity/duration
  • D is incorrect: All systems don’t contribute equally in this event

HMS, BM EQ-Bank 178 MC

A netball player performs a 30-second high-intensity defensive sequence followed by 2 minutes of moderate-intensity play.

Which energy system sequence best represents this activity pattern?

  1. ATP-PCr → Aerobic → Lactic Acid
  2. Lactic Acid → ATP-PCr → Aerobic
  3. ATP-PCr → Lactic Acid → Aerobic
  4. Aerobic → ATP-PCr → Lactic Acid
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\(C\)

Show Worked Solution
  • C is correct:
    • ATP-PCr is first used for the immediate high-intensity defensive moves (0-10 seconds)
    • then the lactic acid system is used for continued high-intensity work (10-30 seconds)
    • finally the aerobic system is relied upon for the moderate-intensity play (30 seconds onwards).

Other Options:

  • A is incorrect: Aerobic would not be the second system engaged
  • B is incorrect: Lactic acid system would not be first in this sequence
  • D is incorrect: Aerobic would not be first for high-intensity work

HMS, BM EQ-Bank 170

How does the rate of recovery between energy systems influence substitution strategies in team sports?   (5 marks)

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Sample Answer

  • The ATP-PCr system recovers rapidly, with phosphocreatine stores replenishing within 2-3 minutes, which allows players to regain explosive power quickly.
  • This fast recovery enables coaches to rotate players for short periods, knowing they can return to perform at maximum intensity.
  • In contrast, the glycolytic system requires much longer recovery as lactic acid must be cleared from muscles.
  • This process takes 30-60 minutes for complete removal, meaning players who have worked at high intensity need extended rest.
  • As a result, substitutions must be timed to prevent lactic acid build-up that would impair performance upon return.
  • The aerobic system recovers based on activity duration, requiring minimal rest for short efforts but longer for extended play.
  • Therefore, coaches use rolling substitutions to maintain fresh ATP-PCr stores for crucial moments.
  • Strategic rest periods ensure key players avoid glycolytic fatigue during important game phases.
  • Consequently, understanding recovery rates helps optimise player rotation and maintain team intensity throughout matches.
Show Worked Solution

Sample Answer

  • The ATP-PCr system recovers rapidly, with phosphocreatine stores replenishing within 2-3 minutes, which allows players to regain explosive power quickly.
  • This fast recovery enables coaches to rotate players for short periods, knowing they can return to perform at maximum intensity.
  • In contrast, the glycolytic system requires much longer recovery as lactic acid must be cleared from muscles.
  • This process takes 30-60 minutes for complete removal, meaning players who have worked at high intensity need extended rest.
  • As a result, substitutions must be timed to prevent lactic acid build-up that would impair performance upon return.
  • The aerobic system recovers based on activity duration, requiring minimal rest for short efforts but longer for extended play.
  • Therefore, coaches use rolling substitutions to maintain fresh ATP-PCr stores for crucial moments.
  • Strategic rest periods ensure key players avoid glycolytic fatigue during important game phases.
  • Consequently, understanding recovery rates helps optimise player rotation and maintain team intensity throughout matches.

HMS, BM EQ-Bank 169

Explain how duration affects the body's utilisation of the three energy systems during a 400 m sprint.   (3 marks)

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Sample Answer

  • Initial 0-10 seconds utilises ATP-PCr system for immediate energy at race start
  • As duration extends to 10-45 seconds, glycolytic system becomes predominant providing energy through glucose breakdown
  • Final stages see increased aerobic contribution as duration approaches 60 seconds though glycolytic remains primary
  • Systems overlap throughout race duration but predominance shifts based on time demands
Show Worked Solution

Sample Answer

  • Initial 0-10 seconds utilises ATP-PCr system for immediate energy at race start
  • As duration extends to 10-45 seconds, glycolytic system becomes predominant providing energy through glucose breakdown
  • Final stages see increased aerobic contribution as duration approaches 60 seconds though glycolytic remains primary
  • Systems overlap throughout race duration but predominance shifts based on time demand

HMS, BM EQ-Bank 165

Compare and contrast how the ATP-PCr and Glycolytic energy systems respond to high intensity exercise.   (4 marks)

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Sample Answer

Similarities:

  • Both systems operate anaerobically, providing ATP without oxygen during maximal efforts.
  • Both support high-intensity exercise when oxygen cannot meet demands.

Differences:

  • ATP-PCr activates instantly for 10-15 seconds while glycolytic takes time to reach peak output.
  • ATP-PCr produces harmless creatine whereas glycolytic generates performance-limiting lactic acid.
  • Recovery differs greatly: PCr replenishes rapidly within minutes versus much longer for lactic acid clearance.
  • ATP-PCr suits explosive single efforts like jumps while glycolytic sustains repeated high-intensity work for 30-90 seconds.
  • Training targets different adaptations: PCr storage capacity versus lactate tolerance.
Show Worked Solution

Sample Answer

Similarities:

  • Both systems operate anaerobically, providing ATP without oxygen during maximal efforts.
  • Both support high-intensity exercise when oxygen cannot meet demands.

Differences:

  • ATP-PCr activates instantly for 10-15 seconds while glycolytic takes time to reach peak output.
  • ATP-PCr produces harmless creatine whereas glycolytic generates performance-limiting lactic acid.
  • Recovery differs greatly: PCr replenishes rapidly within minutes versus much longer for lactic acid clearance.
  • ATP-PCr suits explosive single efforts like jumps while glycolytic sustains repeated high-intensity work for 30-90 seconds.
  • Training targets different adaptations: PCr storage capacity versus lactate tolerance.

HMS, BM EQ-Bank 164

Analyse how different intensities of training can affect energy system adaptations.   (5 marks)

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Sample Answer

  • HIIT increases ATP-PCr stores and phosphocreatine enzyme activity within muscle cells, enhancing the capacity for immediate energy production during explosive movements and repeated short-duration efforts.
  • Training at lactate threshold intensity improves the body’s lactate buffering capacity and tolerance to lactic acid accumulation, enabling athletes to maintain higher intensities for longer periods when relying on glycolytic system energy production.
  • Aerobic training at moderate intensities increases mitochondrial density and size within muscle fibres, improving oxygen utilisation efficiency and the capacity for sustained ATP production through complete glucose and fat breakdown.
  • Varied intensity training programs improve overall energy system efficiency and enhance the smooth transition and interaction between different energy systems during changing exercise demands and intensities.
  • Sport-specific intensity training leads to targeted metabolic adaptations within the predominantly used energy system, such as increased glycolytic enzyme concentration in sprinters or enhanced aerobic capacity in endurance athletes.
  • The principle of training specificity ensures that energy system adaptations closely match the intensity demands and duration characteristics of the athlete’s competitive performance requirements.
Show Worked Solution

Sample Answer

  • HIIT increases ATP-PCr stores and phosphocreatine enzyme activity within muscle cells, enhancing the capacity for immediate energy production during explosive movements and repeated short-duration efforts.
  • Training at lactate threshold intensity improves the body’s lactate buffering capacity and tolerance to lactic acid accumulation, enabling athletes to maintain higher intensities for longer periods when relying on glycolytic system energy production.
  • Aerobic training at moderate intensities increases mitochondrial density and size within muscle fibres, improving oxygen utilisation efficiency and the capacity for sustained ATP production through complete glucose and fat breakdown.
  • Varied intensity training programs improve overall energy system efficiency and enhance the smooth transition and interaction between different energy systems during changing exercise demands and intensities.
  • Sport-specific intensity training leads to targeted metabolic adaptations within the predominantly used energy system, such as increased glycolytic enzyme concentration in sprinters or enhanced aerobic capacity in endurance athletes.
  • The principle of training specificity ensures that energy system adaptations closely match the intensity demands and duration characteristics of the athlete’s competitive performance requirements.

HMS, BM EQ-Bank 162 MC

A tennis player is in a rally lasting 45 seconds at moderate-high intensity. Which energy system sequence best represents their energy production?

  1. Glycolytic → ATP-PCr → Aerobic
  2. Aerobic → ATP-PCr → Glycolytic
  3. ATP-PCr → Aerobic → Glycolytic
  4. ATP-PCr → Glycolytic → Aerobic
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\(D\)

Show Worked Solution
  • D is correct: Shows the natural progression of energy systems as intensity/duration increases

Other Options:

  • A is incorrect: ATP-PCr is the initial energy system
  • B is incorrect: ATP-PCr is the initial energy system and aerobic takes longer to become predominant
  • C is incorrect: Glycolytic precedes Aerobic for moderate-high intensity

HMS, BM EQ-Bank 152

Explain how the interplay of energy systems changes during a 400-metre run.   (4 marks)

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Sample Answer

  • At the start, the ATP-PCr system provides immediate energy for explosive acceleration, lasting only 10-15 seconds.
  • As PCr depletes, the glycolytic system becomes dominant, producing ATP quickly but creating lactic acid build-up.
  • This causes burning sensations and fatigue by 200-300 metres, forcing runners to slow slightly.
  • The aerobic system contributes increasingly throughout, providing baseline energy to support the anaerobic systems.
  • In the final 100 metres, all three systems work together, with glycolytic dominance causing significant fatigue.
  • Therefore, the 400 metre run requires careful pacing to manage the shifting energy system contributions.
Show Worked Solution

Sample Answer

  • At the start, the ATP-PCr system provides immediate energy for explosive acceleration, lasting only 10-15 seconds.
  • As PCr depletes, the glycolytic system becomes dominant, producing ATP quickly but creating lactic acid build-up.
  • This causes burning sensations and fatigue by 200-300 metres, forcing runners to slow slightly.
  • The aerobic system contributes increasingly throughout, providing baseline energy to support the anaerobic systems.
  • In the final 100 metres, all three systems work together, with glycolytic dominance causing significant fatigue.
  • Therefore, the 400 metre run requires careful pacing to manage the shifting energy system contributions.

HMS, BM EQ-Bank 151

Analyse how the availability of different fuel sources affects an athlete's performance in a 90-minute soccer match.   (6 marks)

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Sample Answer

  • The ATP-PCr system provides immediate energy for explosive sprints and tackles in the first few seconds of each high-intensity effort through stored creatine phosphate.
  • During the match, muscle glycogen serves as the primary fuel source, supporting both aerobic activity for general play and anaerobic bursts for sprinting or rapid directional changes.
  • As the match progresses and muscle glycogen becomes depleted, the body increasingly relies on fatty acid oxidation for energy production during lower intensity periods of play.
  • The maintenance of blood glucose levels through liver glycogen breakdown becomes crucial in the latter stages of the match to sustain both physical and mental performance.
  • Players often experience fatigue in the final 15 – 20 minutes of the match due to significant depletion of muscle glycogen stores, resulting in reduced sprint capacity and skill execution.
  • Athletes who engage in carbohydrate loading protocols prior to the match can increase their muscle glycogen stores by up to 50%, thereby delaying the onset of fatigue and maintaining performance intensity throughout the full 90 minutes.
Show Worked Solution

Sample Answer

  • The ATP-PCr system provides immediate energy for explosive sprints and tackles in the first few seconds of each high-intensity effort through stored creatine phosphate.
  • During the match, muscle glycogen serves as the primary fuel source, supporting both aerobic activity for general play and anaerobic bursts for sprinting or rapid directional changes.
  • As the match progresses and muscle glycogen becomes depleted, the body increasingly relies on fatty acid oxidation for energy production during lower intensity periods of play.
  • The maintenance of blood glucose levels through liver glycogen breakdown becomes crucial in the latter stages of the match to sustain both physical and mental performance.
  • Players often experience fatigue in the final 15 – 20 minutes of the match due to significant depletion of muscle glycogen stores, resulting in reduced sprint capacity and skill execution.
  • Athletes who engage in carbohydrate loading protocols prior to the match can increase their muscle glycogen stores by up to 50%, thereby delaying the onset of fatigue and maintaining performance intensity throughout the full 90 minutes.

HMS, BM EQ-Bank 146

Explain how the three energy systems interplay during a 400 metre sprint race.   (6 marks)

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Sample Answer

First 2-3 seconds:

  • The ATP-PCr system provides immediate energy through rapid breakdown of stored phosphocreatine, enabling explosive acceleration from starting blocks without oxygen requirement.

Seconds 3-15:

  • ATP-PCr system remains dominant but begins depleting, with the runner achieving peak velocity as this system provides the highest rate of ATP production for maximum power output.

Seconds 15-30:

  • Glycolytic system becomes predominant as ATP-PCr stores deplete, breaking down muscle glycogen to produce ATP anaerobically, resulting in rapid lactic acid formation.

Seconds 30-45:

  • Continued dominance of glycolytic system with increasing aerobic contribution as oxygen becomes more available, though anaerobic glycolysis still provides majority of energy.

Final 15 seconds:

  • All three systems operate simultaneously with glycolytic system still dominant, but accumulating lactic acid begins interfering with muscle contraction, causing performance decline.

System integration:

  • The transition between systems is gradual rather than distinct, with optimal 400 metre performance requiring efficient switching between energy pathways and the ability to tolerate high lactate levels.

Recovery phase:

  • Post-race recovery involves replenishing ATP-PCr stores (50% within 30 seconds), removing accumulated lactate through aerobic metabolism, and restoring muscle pH levels.
Show Worked Solution

Sample Answer

First 2-3 seconds:

  • The ATP-PCr system provides immediate energy through rapid breakdown of stored phosphocreatine, enabling explosive acceleration from starting blocks without oxygen requirement.

Seconds 3-15:

  • ATP-PCr system remains dominant but begins depleting, with the runner achieving peak velocity as this system provides the highest rate of ATP production for maximum power output.

Seconds 15-30:

  • Glycolytic system becomes predominant as ATP-PCr stores deplete, breaking down muscle glycogen to produce ATP anaerobically, resulting in rapid lactic acid formation.

Seconds 30-45:

  • Continued dominance of glycolytic system with increasing aerobic contribution as oxygen becomes more available, though anaerobic glycolysis still provides majority of energy.

Final 15 seconds:

  • All three systems operate simultaneously with glycolytic system still dominant, but accumulating lactic acid begins interfering with muscle contraction, causing performance decline.

System integration:

  • The transition between systems is gradual rather than distinct, with optimal 400 metre performance requiring efficient switching between energy pathways and the ability to tolerate high lactate levels.

Recovery phase:

  • Post-race recovery involves replenishing ATP-PCr stores (50% within 30 seconds), removing accumulated lactate through aerobic metabolism, and restoring muscle pH levels.