Energy systems - anaerobic and aerobic

Definition:
- The flow of energy in a biological system.
Macronutrients:
- Contain chemical energy that is converted into usable energy for tissues.
- Major substrates include carbohydrates and fats.

Chemical Reactions in the Body:
- Every process in the body consists of a series of chemical reactions.
Catabolism:
- The breakdown of large molecules into smaller ones accompanied by the release of energy.
Anabolism:
- The synthesis of larger molecules using energy provided by catabolic reactions.
Metabolism:
- The overall process of energy transformation in the body.

Adenosine Triphosphate (ATP):
- Known as the energy currency of the body.
- Comprised of three phosphate groups and adenosine.
- Synthesized as the usable form of energy to fuel all activities, irrespective of their duration or intensity.
- Requires a constant and steady supply to function effectively.
Energy Storage in ATP:
- Stored within high-energy bonds in ATP molecules.

Quantity of ATP Stored:
- The human body stores approximately 80-100 grams (3 ounces) of ATP at a time.
- This equates to about 1 billion ATP molecules in each muscle cell, which are used and recycled every two minutes.
- Without the capability to replenish ATP, this amount would be depleted in seconds.
Storage of Macronutrients in the Body:
- Carbohydrates: Stored as glycogen and glucose.
- Fat: Stored within adipose tissue.
- Protein: Present in muscle and as amino acids in the blood.

Three Main Energy Systems:
1. Phosphagen/ATP-PCr/Creatine Phosphate system
2. Glycolysis (can be either Anaerobic or Aerobic)
3. Oxidative Phosphorylation (includes Krebs Cycle + Electron Transport Chain - ETC)
Function of Energy Systems:
- Supply the body with ATP depending on activity intensity and duration.

Energy Continuum:
- Shows the contribution of aerobic and anaerobic systems during various types of physical activities.
Percentage Contribution to ATP Production:
- Aerobic: Efficient for extended activities (e.g., >3 minutes).
- Lactic Acid Glycolysis: Provides energy for activities lasting less than 3 minutes but more than 30 seconds.
- ATP-CP: Provides immediate energy, particularly for short bouts of high-intensity effort (up to 10 seconds).

Anaerobic Processes:
- Do not require oxygen.
- Include Phosphagen system and fast glycolysis.
Aerobic Processes:
- Depend on oxygen availability.
- Include Krebs Cycle, Electron Transport Chain, and Beta Oxidation.

Mitochondria:
- Known as the "powerhouse of the cell," where aerobic metabolism occurs.
Cytoplasm:
- The fluid solution within cells, housing the nucleus and organelles; site of anaerobic metabolism.

Functionality:
- Provides ATP for short-term, high-intensity activities such as sprinting, plyometrics, and weight training.
- Rapidly replenishes ATP and is the quickest energy source, able to fuel around 2 seconds of max effort work.
Mechanism:
- ATP is synthesized from the reaction:
  ADP + PCr
  ightleftharpoons ATP + Creatine (Cr)
- Phosphocreatine (PCr) is 3-4 times more available in muscle than ATP and is located near myosin heads.
- Takes about 3-5 minutes to recover fully after depletion, despite its rapid availability.

Definition:
- The process of converting glucose into energy, occurring through a series of 10 reactions yielding more ATP than phosphagen in longer durations.
- Produces pyruvate and NADH for further ATP generation downstream.
- Occurs in the cytoplasm and does not require oxygen, though conditions can vary based on its availability.
Types of Glycolysis:
1. Fast/Anaerobic Glycolysis:
- Yields 2 (or 3) ATP, 2 NADH, and converts 2 pyruvate to lactate over 15-30 seconds of high-intensity effort with a side effect of H+ ion accumulation.
1. Slow/Aerobic Glycolysis:
- Yields 2 (or 3) ATP, 2 NADH, and converts 2 pyruvate to Acetyl CoA, supplying energy for 30 seconds to 2 minutes.

Initiation Step:
- Glycolysis can start with either glucose or muscle/liver glycogen, indirectly impacting ATP yield.
- Wastes one ATP if starting with glucose (Hexokinase step).
Rate Limiting Step (PFK):
- Step 3 involves investment of 1 ATP, making it the critical regulatory checkpoint.
Subsequent Steps Yield ATP and NADH:
- Step 6 converts glyceraldehyde-3-phosphate to 1,3-bisphosphoglycerate, yielding 1 NADH (2 total).
- Steps 7 & 10 yield a total of 4 ATP (2 from each step) causing net ATP gain after initial losses.

Under Aerobic Conditions:
- Converted to Acetyl CoA.
- Further oxidized with oxygen as the final electron acceptor.
Under Anaerobic Conditions:
- Converted to lactate, whereby lactate signifies H+ accumulation due to an imbalance in lactate dehydrogenase activity.

Lactate is a byproduct of fast glycolysis primarily due to H+ ions.
Accumulation of H+ ions lowers pH affecting muscle contraction and associated pain perception.

Increases linearly with exercise intensity, while lactate accumulation does not.
The lactate threshold signals fast accumulation of lactate, reflecting muscle fatigue but not the direct cause of fatigue itself.

Primary ATP production source at rest and during low-intensity prolonged exercise.
Utilizes carbohydrates and fatty acids, with substrate use varying by exercise intensity.
Total Yield from Oxidative Phosphorylation:
- One molecule of glucose that undergoes glycolysis, citric acid cycle, and oxidative phosphorylation generally yields approximately 38 ATP (+1 for glycogen), but may vary from 32-40 ATP.

Results in varying use of fats versus carbohydrates during exercise, especially as exercises increase in intensity.
Fats yield more ATP through beta-oxidation compared to carbohydrates, which provide a quicker energy source but in lesser quantities.

Carbohydrates:
- Serve as the primary starting materials for glycolysis. Yield pyruvate and eventually Acetyl CoA and NADH.
Fats (FFA):
- Energy-dense, can generate significant ATP through beta oxidation into Acetyl CoA.
Proteins:
- Can enter the citric acid cycle but not typically utilized as a primary energy source unless in dire conditions.