Year 10 HPE – Energy Systems Comprehensive Notes

Warm-Up – Review of Previous Lesson (ATP Cycle)

  • Task: Draw and annotate the ATP cycle.

  • Key stages (to be labelled on diagram):

    • ATP \rightarrow ADP + P_i + \text{ENERGY}

      • ATP hydrolysis releases energy for cellular work (e.g., muscle contraction).

    • ADP + P_i + \text{ENERGY from nutrients} \rightarrow ATP (occurs in mitochondria).

    • Newly formed ATP is immediately available for further work—continuous cycle.

  • Significance: illustrates that all exercise physiology revolves around the constant resynthesis of ATP.

Energy Systems Overview

  • All three systems operate simultaneously; dominance depends on:

    • Intensity of activity.

    • Duration of activity.

    • Athlete’s aerobic fitness (better fitness allows earlier & greater aerobic contribution).

  • Terminology:

    • Anaerobic = without oxygen; rapid ATP, limited capacity, metabolic by-products.

    • Aerobic = with oxygen; slower ATP, very large capacity, minimal fatiguing by-products.

Simplified Matching of Systems to Activity Types

  • ATP-PC: very high intensity, very short (≈10 s) – e.g., 100\,\text{m} sprint.

  • Lactic Acid: high intensity, short–medium (≈60–90 s) – e.g., 400\,\text{m} sprint.

  • Aerobic: low–moderate intensity, long (≥90 s) – e.g., 15\,\text{km} run.

  • Anaerobic: high intensity, short (<90 s) – e.g., sprinting or weightlifting.

1. ATP-PC (Phosphagen) System

  • Classification: Anaerobic.

  • Intensity band: ≈95\% MHR (maximal effort).

  • Duration capacity: 10–15 s before depletion.

  • Physiological mechanism:

    • Stored phosphocreatine (PC) in sarcoplasm donates P_i to ADP → rapid ATP synthesis.

    • Reaction catalysed by creatine kinase.

  • Speed of ATP resynthesis: very fast (immediate power).

  • Fuel availability: only intramuscular PC; limited stores (~90–100 g in trained adult).

  • Example activities: 50 m & 100 m sprints, shot put, basketball jump shot, javelin, discus, explosive starts.

  • Advantages:

    • Instant energy, no lag for oxygen delivery.

    • No harmful by-products.

  • Limitations:

    • PC stores exhausted quickly ⇒ energy drop.

    • Must shift to other systems when PC falls.

  • Recovery:

    • 50\% PC resynthesised ≈ 30 s; 100\% in 2–3 min (passive rest preferred).

    • Requires aerobic metabolism and oxygen availability post-exercise.

  • Training implications: short, maximal bouts with long rests build PC capacity & creatine kinase activity.

2. Lactic Acid (Anaerobic Glycolysis) System

  • Classification: Anaerobic.

  • Trigger: Kicks in as PC depletes (~10–15 s).

  • Intensity band: 85–95\% MHR (moderate-high).

  • Duration capacity: ~60–90 s (depends on tolerance to acidosis).

  • Physiological mechanism:

    • Glycogen or blood glucose → series of enzymatic reactions (glycolysis) → ATP + pyruvate.

    • Without oxygen, pyruvate → lactate + H^+ (lactic acid accumulation).

  • Speed of ATP resynthesis: moderate (slower than PC, faster than aerobic).

  • Fuel: muscle glycogen > blood glucose.

  • Example activities: 400 m sprint, 800 m split, repeated basketball defence, 50 m swim turn.

  • Advantages:

    • Rapid ATP without oxygen when PC gone.

  • Limitations:

    • Lactate and hydrogen ions ↓ pH, inhibit glycolytic enzymes & contractile proteins → fatigue.

    • Clearance/removal can take up to 2 h (active recovery expedites by increasing blood flow & oxidation).

  • Recovery:

    • 1–2 h for lactate levels to return near rest; best aided by light aerobic exercise and hydration.

3. Aerobic (Oxidative) System

  • Classification: Aerobic (requires sustained oxygen supply).

  • Intensity band: <85\% MHR (low–moderate).

  • Duration: dominates >90 s; virtually unlimited if fuel & oxygen supplied.

  • Physiological mechanism:

    • Stage 1: Aerobic glycolysis (glucose → pyruvate with O_2 present; no lactate).

    • Stage 2: Krebs cycle (citric acid cycle) in mitochondria → CO_2, H^+, electrons.

    • Stage 3: Electron Transport Chain (ETC) → large ATP yield via oxidative phosphorylation.

  • Speed of ATP resynthesis: slowest onset, but highest total ATP (≈36–38 ATP/glucose; >100 ATP/fatty acid).

  • Fuels:

    • Short-term: muscle/liver glycogen, blood glucose.

    • Prolonged sub-max: triglycerides (fats) increasingly utilised.

  • Example activities: 15 km jog, marathon, triathlon, continuous cycling, “jog back on defence” between basketball plays.

  • Advantages:

    • Highest ATP yield, diverse fuels, minimal fatigue by-products (mainly CO2 & H2O which are easily removed).

  • Limitations:

    • Slow to activate; reliant on cardiovascular/respiratory delivery of O_2.

    • Cannot sustain very high intensities (>85–90 % MHR).

  • Recovery:

    • Full replenishment of all energy stores (glycogen, fat oxidation by-products) 24–48 h; varies with diet & training level.

Summary Table (Consolidated)

Feature

ATP-PC

Lactic Acid

Aerobic

Oxygen need

Anaerobic

Anaerobic

Aerobic

Intensity (% MHR)

\approx95\%+

85–95\%

<85\%

Dominance duration

0–15 s

15–90 s

>90 s

Example sport actions

100 m sprint, shot put

400 m sprint, repeat basketball defence

15 km run, triathlon

ATP production rate

Fastest

Moderate

Slowest

Capacity (total ATP)

Lowest

Moderate

Highest

Primary fuel

PC

Glucose/Glycogen

CHO & Fats

By-products

None

Lactate + H^+

CO2 + H2O

Full recovery

2–3 min

up to 2 h

24–48 h

Interplay of Energy Systems

  • Principle: All systems are always “on” but proportional contributions shift.

  • Factors determining dominance:

    1. Duration of effort.

    2. Intensity (%MHR, power output).

    3. Individual aerobic fitness & training adaptations.

  • Body’s preference hierarchy: aerobic (efficient) > anaerobic glycolysis > ATP-PC; but intensity can override preference.

  • Graphical concept (as shown in slides):

    • ATP-PC spikes early then drops.

    • Lactic acid rises, peaks around 40–60 s, then tapers.

    • Aerobic rises slowly, becomes dominant >90 s.

Example Percentage Contributions (from slide)

Event

ATP-PC

Lactic Acid

Aerobic

400 m

30\%

50\%

20\%

800 m

20\%

30\%

50\%

Shot Put

98\%

N/A

2\%

Javelin

98\%

N/A

2\%

  • Connects to upcoming units on: muscular fatigue mechanisms, nutrition for sport (carb loading, creatine supplementation), training program design (work:rest ratios for energy system conditioning), and ethical considerations of ergogenic aids (e.g., creatine, blood doping).

Ethical & Practical Implications Discussed

  • Efficient waste removal (aerobic dominance) → health and performance longevity.

  • Over-reliance on anaerobic systems without conditioning raises injury/fatigue risk.

  • Supplementation (creatine) can increase PC stores but must be used responsibly within sport regulations.

Key Equations & Numerical References (LaTeX format)

  • ATP hydrolysis: ATP + H2O \rightarrow ADP + Pi + Energy

  • PC reaction: PC + ADP \xrightarrow{creatine\ kinase} ATP + C

  • Anaerobic glycolysis net yield (per glucose): 2\,ATP + 2\,lactate + 2\,H^+.

  • Aerobic oxidation of glucose: C6H{12}O6 + 6\,O2 \rightarrow 6\,CO2 + 6\,H2O + 36\text{–}38\,ATP.

  • Aerobic oxidation of palmitic acid (example fat): C{16}H{32}O2 + 23\,O2 \rightarrow 16\,CO2 + 16\,H2O + >100\,ATP.