Energy systems for exercise: ATP-PC, glycolytic and oxidative
Muscle runs only on ATP. Three systems rebuild it: ATP-PC for about 10 seconds, glycolysis up to about 2 minutes, and the oxidative system beyond that.
The energy continuum
All three systems work at the same time. Intensity and duration decide which one leads.
Comparison of the three energy systems
| Feature | ATP-PC | Anaerobic glycolysis | Oxidative |
|---|---|---|---|
| Oxygen needed | No | No | Yes |
| Fuel | Phosphocreatine | Glucose and muscle glycogen | Carbohydrate, fat, a little protein |
| Site | Cytoplasm | Cytoplasm | Mitochondria |
| Rate of ATP supply | Fastest | Fast | Slowest |
| Capacity | Very small | Limited | Very large |
| ATP yield | 1 ATP per PCr | Net 2 per glucose (3 per glucose unit from glycogen) | About 30-32 per glucose; about 106 per palmitate |
| By-products | Creatine | Lactate and hydrogen ions | Carbon dioxide and water |
| Leads in efforts of | Up to about 10 s | About 10 s to 2 min | Beyond about 2 min |
| Recovery | PCr about half restored in 30 s, nearly full in a few minutes | Lactate mostly cleared within about an hour; sooner with an easy cool-down | Not limited by a store |
| Sport examples | 100 m, shot put, javelin, high jump, a fast bowler's delivery | 400 m, 100 m swim, a 30-second kabaddi raid | Marathon, 10,000 m, road cycling, a full hockey match |
Key reactions
- 1ATP → ADP + Pi + energy for the cross-bridge stroke.ATPase
- 2★PCr + ADP → ATP + creatine: the fastest way to rebuild ATP.Creatine kinase
- 3ADP + ADP → ATP + AMP: a small backup when ADP piles up.Myokinase (adenylate kinase)
- 4★Glucose → 2 pyruvate + net 2 ATP + 2 NADH in the cytoplasm.Phosphofructokinase is the rate-limiting enzyme
- 5Pyruvate → lactate when pyruvate is made faster than mitochondria can use it; this regenerates NAD+ so glycolysis can continue.Lactate dehydrogenase
- 6★Pyruvate → acetyl-CoA → Krebs cycle → electron transport chain → ATP, CO2 and water, in the mitochondria.
- 7Fatty acids → beta-oxidation → acetyl-CoA → Krebs cycle: slow, needs oxygen, but gives a very large ATP yield.
★ one-way, controls the pace
Energy systems in Indian sports
| Sport | Main systems | Diet focus |
|---|---|---|
| Sprints, shot put, javelin, weightlifting | ATP-PC | Protein, enough carbohydrate, creatine stores |
| Kabaddi | ATP-PC and glycolysis in each raid; oxidative between raids | Carbohydrate for repeated efforts, protein, fluids |
| Hockey and football | All three (stop-and-start) | High carbohydrate, fluids, recovery snacks |
| Cricket fast bowling | ATP-PC for each ball; oxidative over a long spell | Carbohydrate and fluid spread across the day |
| 400 m and 800 m | Glycolysis with a large oxidative share | Full glycogen; buffers such as beta-alanine or bicarbonate |
| Marathon and long-distance | Oxidative | Carbohydrate loading, carbohydrate during the race, fluids |
The energy system shapes the diet: ATP-PC athletes (throwers, sprinters) benefit from creatine stores and protein, glycolytic events need full glycogen and buffering, and oxidative events need carbohydrate loading, carbohydrate during the race and fluids. Vegetarian athletes have lower muscle creatine, since food creatine comes mainly from meat and fish.
2 marks: “What is the phosphagen (ATP-PC) system?” PCr gives its phosphate to ADP to rebuild ATP (creatine kinase). It needs no oxygen and powers maximal efforts of up to about 10 seconds.
5 marks: “Compare the aerobic and anaerobic energy systems.” Table of oxygen use, fuel, site, rate, capacity, ATP yield, by-products, duration and sport examples.
10 marks: “Explain the energy systems used during exercise with a neat diagram. Give sports examples for each.” Energy continuum diagram, then each system's reaction, rate, capacity, yield, duration and examples, a comparison table and a diet note.
10 seconds, 2 minutes, beyond: PCr powers the sprint, glycolysis the 400 m, oxygen the marathon.