ATP Resynthesis Pathways and Creatine Supplementation

ATP Resynthesis Pathways

• Phosphagen system: Creatine phosphate (PCr) is used to quickly regenerate ATP.
  • Occurs in the cytoplasm of muscle cells.
  • Provides energy for short bursts of intense activity (e.g., weightlifting, sprinting).
• Glycolysis: Breakdown of glucose into pyruvate, producing a net of 2 ATP molecules.
  • Occurs in the cytoplasm of muscle cells.
  • Important for moderate-intensity exercise lasting up to 3 minutes.
• Oxidative phosphorylation: Series of metabolic reactions occurring in the mitochondria.
  • Uses oxygen to generate ATP from glucose, pyruvate, and fatty acids.
  • Provides energy for long-duration, low-intensity activities (e.g., jogging, cycling).

Creatine Supplementation

• Creatine supplementation can temporarily increase PCr stores in muscles.
• Effective for improving performance in activities requiring short bursts of high intensity.

Glycolysis Details

• Inputs: Glucose.
• Outputs: 2 pyruvate molecules, 2 ATP, and 2 NADH.
• Key Enzyme: Phosphofructokinase (PFK) is the rate-limiting enzyme.
• Sources of glucose: Muscle glycogen, blood glucose (maintained by liver glycogen and food intake).
• Glucose uptake: Influenced by insulin, exercise intensity, and GLUT-4 transporter.

Pyruvate Fates

• Lactate formation: Occurs when oxygen supply is limited.
  • Used to maintain a fast rate of glycolysis.
• Oxidative metabolism: Enters the mitochondria for further energy production.

The Citric Acid Cycle

• Occurs in the mitochondria.
• Breaks down pyruvate to generate energy.
• Produces ATP, NADH, and FADH2 which are used in the electron transport chain.

The Electron Transport Chain

• Occurs in the mitochondria.
• Uses electrons from NADH and FADH2 to generate a proton gradient.
• This gradient is used to produce ATP.
• Requires oxygen as the final electron acceptor.

Carbohydrate Digestion and Absorption

• Monosaccharides: Simple sugars (e.g., glucose, fructose, galactose).
• Disaccharides: Two simple sugars linked together (e.g., sucrose, lactose, maltose).
• Polysaccharides: Long chains of simple sugars (e.g., starch, glycogen).
• Dietary fiber: Indigestible carbohydrates, contribute to digestive health.

Muscle vs. Liver Glycogen

• Muscle glycogen: Provides energy directly to muscle cells.
• Liver glycogen: Regulates blood glucose levels, supplying glucose to the bloodstream during fasting or low energy conditions.

Carbohydrate Loading

• Classical method: Depletes glycogen stores followed by high-carbohydrate intake.
• Modified method: Gradual carbohydrate increase over several days.
• Disadvantages of classical method: May lead to muscle fatigue and discomfort.

Glycemic Index (GI)

• Measure of how quickly a food raises blood glucose levels.
• High GI foods are rapidly digested and absorbed.
• Low GI foods are digested and absorbed more slowly.

Carbohydrate Intake Recommendations Before Exercise

• 1-4 hours before exercise: High-carbohydrate meals or snacks (e.g., pasta, potatoes, fruit) to maximize glycogen storage and provide glucose for intestinal absorption.

Carbohydrate Intake During Exercise

• Duration and intensity: Crucial factors determining the need for carbohydrate intake during exercise.
• Liquid form: Provides rapid absorption and gastric emptying.
• Solid form: More energy dense but can cause slower digestion.
• Combined forms: Mixes of liquid and solid forms of carbohydrates.

Glycogen Resynthesis after Exercise

• Rapid phase: Occurs within the first 2 hours after exercise.
• Slow phase: Occurs from 2 to 24 hours after exercise.

Factors Affecting Glycogen Resynthesis Rate

• Insulin: Increases glucose uptake and glycogen synthesis.
• GLUT-4: Transporter responsible for glucose uptake in muscle cells.
• Glycogen synthase: Enzyme that catalyzes glycogen synthesis.

Carbohydrate Intake Recommendations After Exercise

• Immediate: Consume carbohydrates to facilitate glycogen resynthesis.
• Later events: Consume carbohydrates to ensure adequate glycogen stores for subsequent exercise.

Daily Carbohydrate Recommendations for Athletes

• Moderate to heavy training: 5-10 grams of carbohydrate per kilogram of body weight per day.

Fat Metabolism

• Lipolysis: Breakdown of triglycerides into fatty acids and glycerol.
• Key enzyme: Hormone-sensitive lipase (HSL).
• Activation: Triggered by hormones (e.g., adrenaline, cortisol) and low insulin levels.
• Transport: Fatty acids are transported in the bloodstream bound to albumin.

Crossover Concept

• As exercise intensity increases, the body relies more on carbohydrates as a primary source of fuel.
• The crossover point is when 50% of energy is derived from carbohydrates and 50% from fat.
• Endurance training shifts the crossover point to the right, allowing athletes to utilize fat as fuel for longer periods.

Fat Oxidation and Training

• Mitochondrial adaptation: Increases in mitochondrial enzymes improve oxidative capacity.
• Cellular transport: Improved uptake of fatty acids from the bloodstream.
• Cardiovascular improvements: Increased blood flow and oxygen delivery to muscles.

Low-Carb, High-Fat Diet

• Adaptation: Liver produces ketone bodies from fatty acid breakdown.
• Brain fuel: Ketones become the primary energy source for the brain.
• Increased protein needs: Glycogen stores are depleted, leading to increased protein breakdown to provide energy.

Ketone Bodies

• Formed in the liver from fatty acids.
• Used as an alternative fuel source by tissues like the brain.

LCHF Effects on Exercise Performance

• Increased fat oxidation: Spares glycogen stores allowing for longer endurance.

Medical Conditions

• Epilepsy: Low-carb, high-fat diets may reduce seizures.

Explore the various pathways of ATP resynthesis including the phosphagen system, glycolysis, and oxidative phosphorylation. Learn how creatine supplementation can enhance performance in high-intensity activities and its impact on muscle energy. This quiz is ideal for students studying exercise physiology or related fields.