Energy Systems - Fueling the Fire
ATP regeneration for exercise uses three systems, based on intensity and duration:
| Feature | ATP-PCr (Phosphagen) | Anaerobic Glycolysis | Aerobic System (Oxidative) |
|---|---|---|---|
| Onset | Immediate | Rapid | Slower |
| Duration | <10-15s (Maximal effort) | ~1-2 min (High intensity) | >2 min (Sustained) |
| ATP Yield | Very Low (1/PCr) | Low (2/glucose) | High (32+/glucose) |
| Power | Highest | High | Moderate/Low |
| Fuel | PCr | Glucose/Glycogen | Glucose, Fats, Amino Acids |
| Reaction | $PCr + ADP + H^+ \leftrightarrow ATP + Cr## Energy Systems - Fueling the Fire |
ATP regeneration for exercise uses three systems, based on intensity and duration:
| $Glucose \rightarrow 2ATP + 2Lactate## Energy Systems - Fueling the Fire
ATP regeneration for exercise uses three systems, based on intensity and duration:
| Krebs & Oxidative Phos. | | Examples | Sprints, lifts | 200-800m races | Endurance (Marathon) |> ⭐ Creatine phosphate (PCr) system provides ATP for the initial ~10-15 seconds of maximal intensity exercise, acting as the most rapid ATP buffer.
- Systems overlap; contribution varies with exercise type.
Hormonal Regulation - Conductors of Change
Key hormones adapt to fuel exercise demands. 📌 CAGE: Hormones ↑ in exercise: Cortisol, Adrenaline (Catecholamines), Glucagon. Growth Hormone also ↑.
| Hormone | Source | Stimulus (Exercise) | Major Actions (Exercise) | Trend |
|---|---|---|---|---|
| Insulin | Pancreas (β-cells) | ↓ SNS, ↑ Catecholamines (α-eff) | ↓ Glucose uptake (inactive), ↓ Anti-lipolysis | ↓ |
| Glucagon | Pancreas (α-cells) | ↑ Catecholamines, ↓ Glucose | ↑ Hepatic glycogenolysis & gluconeogenesis | ↑ |
| Catecholamines | Adrenal Medulla/SNS | ↑ SNS activity | ↑ Glycogenolysis, ↑ Lipolysis, ↑ Glucagon, ↓ Insulin | ↑ |
| Cortisol | Adrenal Cortex | ↑ ACTH (stress) | ↑ Proteolysis, ↑ Gluconeogenesis, ↑ Lipolysis (permissive) | ↑ |
| Growth Hormone | Anterior Pituitary | ↑ Intensity/duration, ↓ Glucose | ↑ Lipolysis, ↑ Gluconeogenesis, ↓ Glucose uptake | ↑ |
Tissue-Specific Metabolism - Cellular Symphony
- Skeletal Muscle:
- Fuel shift: Initial glucose (glycogen) → FFAs (adipose/IMTG) → Ketones (prolonged, intense).
- GLUT4 translocation: Insulin-independent (contraction via AMPK) & insulin-dependent.
- Lactate: $Pyruvate + NADH \leftrightarrow Lactate + NAD^+$. Cori cycle or oxidized by other tissues.
- BCAA oxidation for energy.
- Liver:
- Maintains blood glucose: Hepatic glycogenolysis & gluconeogenesis (substrates: lactate, alanine, glycerol).
- Urea cycle: Detoxifies ammonia ($NH_3$) from amino acid catabolism.
- Ketogenesis: During prolonged, high-intensity exercise.
- Adipose Tissue:
- Lipolysis ↑: Catecholamines activate HSL → FFAs + Glycerol released.
- FFAs (albumin-bound) fuel muscles; Glycerol for hepatic gluconeogenesis.
⭐ AMPK (AMP-activated protein kinase): Master metabolic regulator. Activated by ↑ AMP/ATP ratio during exercise. Stimulates glucose uptake (GLUT4 translocation) & fatty acid oxidation in muscle.
Adaptations to Training - Built to Last
- Chronic exercise: specific, lasting metabolic & physiological changes.
- Endurance Training (ET) adaptations:
- ↑ Muscle glycogen & intramuscular triglyceride (IMTG) stores
- ↑ Oxidative enzyme activity (e.g., citrate synthase)
- ↑ Mitochondrial density & biogenesis (PGC-1α mediated)
- ↑ Capillary density; ↑ $VO_2$ max
- Fiber type: IIx → IIa shift; ↑ Type I characteristics
- Enhanced fat oxidation, glycogen sparing.
- Resistance Training (RT) adaptations:
- ↑ Muscle glycogen stores
- ↑ Glycolytic enzyme activity (e.g., PFK)
- Muscle hypertrophy (↑ fiber cross-sectional area)
- ↑ Strength & power
- Minimal change: mitochondrial density, $VO_2$ max (vs ET)
- Fiber type: IIx → IIa shift.
⭐ Endurance training significantly increases mitochondrial biogenesis (e.g., via PGC-1α) and capillary density in muscles, enhancing oxidative capacity and leading to glycogen sparing.
vs. resistance training (fiber hypertrophy))
High‑Yield Points - ⚡ Biggest Takeaways
- ATP demand ↑↑; phosphocreatine provides immediate ATP.
- Muscle glycogen for initial burst; liver glycogenolysis & gluconeogenesis sustain blood glucose.
- Hormonal milieu: ↑ glucagon, epinephrine, cortisol; ↓ insulin, favoring catabolism.
- AMPK activation is crucial: ↑ glucose uptake (muscle), ↑ fatty acid oxidation.
- Prolonged exercise: ↑ reliance on fatty acid oxidation from adipose stores.
- Lactate is a key fuel (Cori cycle, direct oxidation), not just waste_._
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