Energy Systems, ATP, Fibre Types, Aerobic vs Anaerobic Basics

What happens when ATP splits?

ATP → ADP + inorganic phosphate, releasing energy for muscle contraction and movement.

Why is ATP important for physiotherapy?

Exercise prescription must match patient goals, capacity, and recovery stage — ATP availability influences endurance, strength, and fatigue.

Which muscle fibres should be trained early in rehab for endurance goals?

Type I slow-twitch + Type IIa intermediate fibres (lower load, longer duration exercise).

Which muscle fibre type is used in explosive power exercises?

Type IIx fast-twitch fibres (recruited in high‑intensity, fast, powerful movements).

Where does aerobic energy production occur?

In the mitochondria using oxygen to produce large amounts of ATP (slow but efficient).

What are the two main aerobic metabolic cycles?

Krebs (Citric Acid) cycle + Electron Transport Chain (ETC).

How fast is ATP produced by the aerobic system?

Slow rate but produces a large amount of ATP.

Where are glycogen stores found?

In the liver and muscles; used for anaerobic and aerobic metabolism.

How long do glycogen stores take to replenish?

Approx. 5-40 hours depending on intensity and nutrition.

What tests measure anaerobic power?

Jump tests, Wingate test (30‑sec cycling sprint), and 1RM strength testing.

How does exercise increase glucose uptake for diabetes management?

ATP breakdown → ADP → enzyme activation → GLUT‑4 moves to the membrane → ↑ glucose uptake.

Which type of training best stimulates GLUT‑4?

Interval training (e.g., 45‑sec bouts), which decreases ATP and increases insulin sensitivity.

What fuels can mitochondria use for aerobic metabolism?

Carbohydrates, fats, and proteins → all converted into acetyl‑CoA → enter Krebs cycle.

What is the main by‑product of aerobic metabolism?

Carbon dioxide (CO₂).

Why can fat fuel long-duration exercise?

Fat yields high energy and is stored as triglycerides; breakdown requires lots of oxygen, so it's used in low-intensity activity.

What is brown fat?

Metabolically active fat that burns more energy than white fat.

What is pyruvate used for?

Pyruvate (from glycolysis) → converted to acetyl‑CoA → enters aerobic metabolism for ATP production.

What tests assess aerobic capacity?

Walking tests + cycle tests (low impact).

What happens to VO₂ during exercise?

VO₂ increases because metabolic demand and O₂ use rise.

What does VO₂ measure?

Oxygen consumed per minute (indicator of aerobic metabolism).

What does VCO₂ measure?

Carbon dioxide produced per minute.

How do physiotherapists determine energy system use?

Using a metabolic mask measuring VO₂ and VCO₂.

What indicates fat burning in terms of VO₂ and VCO₂?

VO₂ is high relative to VCO₂.

What indicates carbohydrate burning?

VO₂ is low relative to VCO₂.

What does RER > 1 mean?

Glycolysis dominant → carbohydrates used → anaerobic metabolism.

What does RER < 1 mean?

Fat use dominant → aerobic metabolism.

What is the anaerobic threshold?

When the body shifts from fat → carbohydrate as primary fuel (RER rising towards 1).

What is the main fuel at low intensity?

Fats (via beta‑oxidation requiring high oxygen).

What happens as intensity increases towards moderate?

Mix of fats + carbohydrates; RER rises but stays under 1.

What does glycolysis produce during high intensity?

Hydrogen ions (H⁺) which can strain metabolism.

What forms lactate?

Pyruvate + hydrogen ions → lactate (when energy demand exceeds aerobic capacity).

What causes ventilation to spike at high intensity?

CO₂ increases at the ventilatory anaerobic threshold → breathing rises sharply.

What is the lactate threshold?

Point where lactate production > lactate clearance → shift to anaerobic metabolism.