2/26 exercise phys

Recap on Fatigue and Depletion Hypotheses

• We discussed neural fatigue, which is a depletion of acetylcholine (ACH) at the neuromuscular junction.

• Focused on fatigue during maximal or near-maximal intensity exercise and implications of creatine supplementation.

Depletion Hypothesis

• Involves two main factors:

  • Neurophagy: Breakdown of neural cells due to fatigue.

  • Energy Substrate Depletion: Involves depletion of energy sources, particularly phosphagen stores and glycogen.

Glycogen Depletion

• Glycogen: Stored glucose. It’s a polymer of glucose molecules, enabling efficient energy storage.

• Important in endurance activities (e.g., marathons, triathlons) where carbohydrate oxidation is the primary energy source.

  • Average person has ~2,000 kilocalories stored in muscles as glycogen.

  • Roughly 100 kilocalories per mile burned, regardless of pace.

• Marathon runners often experience "hitting the wall" when glycogen stores are depleted, requiring reliance on less efficient fatty acids for energy.

Glycogen Supercompensation

• Glycogen Supercompensation: Also known as carbohydrate loading, it enhances glycogen stores.

• Involves depleting glycogen stores through exercise, followed by a high-carbohydrate intake for enhancement before an event.

  • Example: Marathon preparations typically involve a rigorous exercise and diet regimen leading up to the race.

• Runners often run at race pace for approximately 20 miles to deplete glycogen reserves before loading on carbohydrates to maximize store recovery.

• Those completing this cycle well may experience up to a 50% increase in glycogen storage.

Muscle Contraction Mechanism

• Muscle tension arises from the interaction of actin and myosin within sarcomeres.

• Contraction occurs as myosin heads swivel, pulling Z lines closer together.

• Current from the motor cortex travels through upper motor neurons to lower motor neurons, with ACH being the key neurotransmitter.

  • ACH triggers muscle contraction once it binds to receptors on the muscle fiber.

• After binding, ATP must bind to the myosin head to break the actin-myosin bond allowing for continued contraction cycling.

Metabolism in Exercise

• ATP: Central to all voluntary human movement.

• Importance of understanding ATP’s role in muscle contraction and its production pathways, aerobic and anaerobic.

• Metabolism: Refers to the biochemical processes resulting in energy production from food through:

  • Anabolic Processes: Building up energy reserves.

  • Catabolic Processes: Breaking down substrates for energy use.

• Anaerobic ATP Production involves:

  • ATP-PC System: Immediate energy supply.

  • Anaerobic Glycolysis: Breakdown of glucose without oxygen, yields lactic acid.

• Aerobic ATP Production: Occurs in mitochondria and involves the Krebs cycle. Requires oxygen and processes fat and carbohydrates for energy.

  • Phosphogens cannot be aerobically metabolized.

Conclusion

• Anything discussed relating to fatigue, depletion, and glycogen metabolism is relevant for the first exam.

• Next topics will explore metabolism further.