Year 10 – Energy Systems Comprehensive Notes

ATP (Adenosine TRI-phosphate) is the universal cellular energy currency.
Energy release equation (occurs in fractions of a second):
ATP \;\xrightarrow{\text{break bond}}\; ADP + P_i + \text{Energy}
All muscular contractions ultimately rely on this breakdown.
Free ATP stored in muscles/liver lasts ≈ 2–3 s of maximal effort.

Two broad pathways to re-form ATP:
- Anaerobic – does not require O_2 (ATP–PC, Lactic Acid).
- Aerobic – requires O_2 (Aerobic system).
Key determinants of which system dominates: exercise intensity & duration.
Duration guidelines (dominant, not exclusive):
- 0–10 s → ATP–PC
- 10 s–≈ 3 min → Lactic Acid
- >5 min → Aerobic

Fastest but least efficient pathway; no lactic acid produced.
Fuel: stored Phosphocreatine (PC) in muscle.
Key reaction:
ADP + PC \rightarrow ATP + C (catalysed by creatine kinase).
Time capacity: ≈ 8–10 s of explosive work; PC depleted quickly.
Recovery: PC resynthesises to ≈ 98 % after 3 min rest (requires aerobic metabolism).
Primary fitness components: muscular power, speed, anaerobic power.
Typical activities: 100 m sprint, javelin throw, dive start in swimming, heavy 1-RM lift, football tackle burst.

Begins when PC stores fall; breaks down glucose/glycogen without O_2.
Process: Glycolysis → ATP + lactic acid.
Time capacity: ≈ 2–3 min at high intensity.
Lactic acid ↔ dissociates → H^+ ions → ↓ pH → muscle fatigue (heavy, burning feeling).
Primary fitness components: muscular power, speed endurance, anaerobic power.
Typical activities: 400–800 m run, repeated netball or football sprints, home-run dash, chasing a ball in fielding.

Most efficient & sustainable; slowest ATP turnover.
Requires continuous oxygen supply.
Fuel hierarchy (intensity dependent):
1. Carbohydrates (glucose/glycogen)
2. Fats (FFA, triglycerides)
3. Proteins (minimal, extreme cases).
Process: Glycolysis → Krebs Cycle → Electron Transport Chain → large yield of ATP (≈ 36–38 per glucose) without lactic acid.
Time capacity: 5 min → hours (marathon, cycling, sitting).
Primary fitness components: aerobic power, muscular endurance, LME (local muscular endurance).

Energy system | Time/Duration | Predominant Fitness Components | Typical Uses/Exercises | Advantages | Disadvantages | Other Info
ATP–PC | 0–10 s | Power, Speed | 100 m sprint, weight-lifting, dive start | Fastest, no O_2 needed | Very limited store, lowest total ATP | 98 % PC recovery ≈ 3 min
Lactic Acid | 10 s–3 min | Power, Speed Endurance | 400 m, team-sport bursts | Moderate ATP rate, no O_2 needed | Lactic acid → fatigue | Uses muscle glycogen
Aerobic | > 5 min | Aerobic Power, Endurance | Marathon, long ride | Produces most ATP, long duration | Slowest rate, can’t fuel sprints | Switches fuels; needs O_2

Systems overlap & co-operate; dominance shifts continuously.
Example: 1500 m swim start
- Dive off blocks = ATP–PC
- Settle into pace = Aerobic.
Football: high-speed run/tackle (ATP–PC) → jogging/positioning (Aerobic) → repeated throughout match.

Softball
- ATP–PC: batting swing, throw to base, sprint to base.
- Lactic Acid: long chase to retrieve ball, full-field home run.
- Aerobic: standing/set-up time between plays.
Weight-lifting: single maximal lift → ATP–PC.
400 m track: first 10 s ATP–PC, remainder Lactic Acid.
Marathon: predominantly Aerobic; ATP–PC only for surges/finish sprint.

ATP–PC
- ✔ Fastest; no O_2 required; supports very powerful moves.
- ✖ Depletes in < 10 s; least efficient (smallest ATP yield).
Lactic Acid
- ✔ Moderate ATP yield & duration; no O_2 needed.
- ✖ Lactic acid accumulation → fatigue; limited to ≈ 3 min.
Aerobic
- ✔ Highest ATP yield; fuels hours of work; efficient.
- ✖ Slow rate; cannot sustain high-intensity, maximal efforts.

Immediate ATP store ≈ 2 s.
ATP–PC dominant window ≈ 0–10 s.
Lactic Acid dominant window ≈ 10 s–3 min.
Aerobic dominant window ≈ >5 min (up to >2 h continuous).
Energy contribution figure (typical):
- ATP store – 2 s
- ATP–PC – 10 s
- Lactic – 2 min
- Aerobic – 2 h +