3.3 Energy Systems - Sports Science

ATP

The body's energy currency; made of adenosine and three phosphate groups; energy is released when a phosphate bond is broken

ATP synthesis

ADP + phosphate + energy → ATP; energy is released when ATP is broken back down to ADP + phosphate

Role of ATP in muscle contraction

ATP binds to myosin heads to enable cross-bridge cycling; also needed to detach myosin from actin and to power the sodium-potassium pump

ATP-CP system

Creatine phosphate donates a phosphate to ADP to rapidly regenerate ATP; requires no oxygen; lasts approximately 10 seconds; used in explosive short efforts

Lactic acid system

Glucose is broken down via glycolysis to produce pyruvate, which is converted to lactate and ATP; no oxygen required; produces 2 ATP per glucose; lasts 10–90 seconds

Oxygen deficit

The difference between the oxygen required at the start of exercise and the oxygen actually consumed; occurs because the aerobic system takes time to reach full capacity

EPOC (oxygen debt)

Excess post-exercise oxygen consumption; elevated oxygen uptake after exercise used to restore ATP-CP stores, remove lactate, and return the body to homeostasis

Aerobic system using glucose

Glucose → glycolysis → Krebs cycle → electron transport chain; produces approximately 36–38 ATP plus CO2 and water

Aerobic system using fatty acids

Triglycerides are broken down via lipolysis → beta-oxidation → Krebs cycle → electron transport chain; produces a very large ATP yield

ATP-CP system characteristics

Fastest ATP production; very short duration (~10 seconds); no oxygen needed; no fatiguing byproducts; used in sprints, jumps, and throws

Lactic acid system characteristics

Fast ATP production; lasts 10–90 seconds; no oxygen needed; produces lactate and hydrogen ions causing fatigue; used in 400m, rowing

Aerobic system characteristics

Slowest ATP production; unlimited duration; requires oxygen; uses glucose, fat, and protein; produces CO2 and water; used in marathon, cycling

Energy system contributions

All three systems are always active; the dominant system depends on exercise intensity and duration; high intensity favours ATP-CP and lactic acid; low intensity long duration favours the aerobic system