Krebs Cycle and Exercise Physiology Quiz

Aerobic Power (VO2max) Definition

• VO2max is the best index of cardiovascular fitness.
• It represents the maximum capacity for oxygen uptake and ATP regeneration during exercise.

VO2max Dependence

• The ability of the cardiovascular system to deliver oxygen to the muscles.
• The capacity of working muscles to extract and utilize oxygen to produce energy through aerobic metabolic pathways.
• Mathematically, VO2max = COmax • a-vO2Dmax (where variables represent maximal cardiac output and arterial-venous oxygen difference).

Aerobic Power (Continued)

• It is important for sustaining high-intensity exercise because aerobic ATP synthesis rate depends on oxygen consumption rate.
• More critical for endurance events (like a marathon or miler) than shorter high-intensity sprints (like a mile).

VO2max During a Mile Race

• Reaching VO2max (or more) during the final 400 meters of a mile race indicates high aerobic capacity.
• This high capacity allows for high rates of ATP yield, supporting fast crossbridge cycling (fast-twitch muscle contraction).
• It also permits supporting "aggressive" neuromuscular drive by an equivalent metabolic response.

Glycolysis and Acidosis in Mile Racing

• During a mile race, glycolysis significantly increases, leading to an increase in acidosis (lower pH) values.
• Milers can better handle the resulting short-lived pH challenge due to their developed glycolytic buffering capacity.

VO2max and Marathon

• VO2max is a secondary factor in marathon success.
• The slower yet fast pace of a marathon doesn't necessitate the same high rate of aerobic ATP synthesis as a mile race.
• A higher lactate threshold expressed at a high percentage of VO2max is crucial for success.

Best Competitor in Aerobic Events

• The best competitor in aerobic events with similar VO2max values is typically the one who can sustain aerobic energy production at the highest percentage of their VO2max without accumulating large amounts of lactic acid in the muscles and blood.

Lactate Threshold (LT) With Training

• A higher percentage of VO2max for lactate threshold (LT) results in a higher pace needed to reach that threshold.
• The higher the percentage, the better trained a person is considered to be.

Aerobic Glycolysis

• Involves initial glycolysis in the cytoplasm/sarcoplasm which proceeds to the mitochondria.
• The Krebs Cycle and ETC play essential roles in this stage.
• Net ATP from blood glucose is 32, and from muscle glycogen, it is 33.

Krebs Cycle

• Completes the oxidation of fuel nutrients.
• Occurs in the mitochondrial matrix.
• Continues pyruvate metabolism.
• Consists of 8 steps including oxidation/reduction and decarboxylation leading to Citrate as first intermediate, and oxaloacetate as the last.
• Generates 3 NADH and 1 FADH₂ per cycle.
• Produces ATP through substrate-level phosphorylation.

Electron Transport Chain (ETC)

• Oxidative phosphorylation occurs in the ETC.
• Oxidative reactions couple with the phosphorylation of ADP.
• Phosphorylation of ADP is driven by oxidation of reduced electron carriers.

Source of Reduced Electron Carriers

• NADH and FADH₂ carry electrons to the ETC.
• These are produced during glycolysis and the Krebs cycle.

Electron Transport Chain Process

• Electrons from NADH and FADH₂ move through the ETC .
• This energy is used to pump H+ (protons) into the outer compartment of the mitochondria.
• The H+ diffuses back to the inner compartment through ATP synthase (channels).
• ATP synthase couples H+ movement to ATP production.
• O₂ combines with H+ and electrons to form water.

Lipid Metabolism

• Fats are only metabolized aerobically.
• Crucial roles for the Krebs Cycle, ETC and oxidation.
• Net ATP production per molecule of palmitate is 129.
• Fat oxidation in the Krebs Cycle is possible only when enough oxaloacetate is available.
• Fats require the "flame" of carbohydrates for oxidation.

Lipid Oxidation

• Degradative pathway that is cyclic.
• Cleaves 2 carbons from the fatty acid per cycle starting at the COOH end.
• Releases 1, 2-carbon ACoA per cycle.
• Produces 1 FADH₂ and 1 NADH per cycle.

Substrate Utilization During Exercise (Crossover Concept)

• During exercise, the body shifts from fatty acid use to carbohydrate use as intensity increases (cross-over).
• The shift is due to FT fiber recruitment and increase in catecholamines/Calcium.

Crossover Concept (Continued)

• Glycolysis is accelerated by catecholamines and Calcium.
• Increased glycolytic activity during intense exercise reduces the ability to utilize fat as fuel.
• Lactate and H+ influence FFA (free fatty acid) mobilization from adipose cells.
• Fat can only provide substrate at ~60-75% VO2max

Determining Training Intensity (Most Important Variable)

• An intensity threshold is needed for training adaptations and performance gains.
• Factors other than intensity, like mode, duration, and frequency, matter in training.

Determining Intensity (Continued)

• Competition occurs around (and beyond) the lactate threshold, especially during sustained high-intensity efforts.
• Training should improve both aerobic and anaerobic qualities (i.e., both mitochondrial and sarcoplasmic reactions).

Intensity Regulation

• Accurate intensity regulation involves recording VO2 during exercise (to evaluate the percentage of VO2max).
• Assessing blood lactate concentration is important to understand how training intensity relates to the lactate threshold.
• Heart rate can be used when equipment is not available.
• HR correlates with metabolic rate (VO2).

HR Methods (Various)

• Percentage of maximum heart rate (MHR) method.
• The Karvonen method (based on heart rate reserve- HRR), for determining training intensity.
• Both HRR and MHR methods need factors (e.g., trained state or training session stage) to be considered.
• Training intensity zones can be re-computed based on changes in resting heart rate.

Lactate Threshold Method

• A training and competition intensity measure.
• Train at a near-lactate threshold HR (or pace).

Determining Duration (Principles and Factors)

• Duration depends on many variables like training method, intensity, volume, and the training phase one is in.

Components of an Aerobic Training Session

• Warm-up: Warm-up, stretching, and calisthenics.
• Workout/Competition
• Cool-down: Light-intensity exercises and stretching to aid recovery.

Active vs. Passive Cooldowns

• No difference in lactate clearance between active or passive cooldowns for an hour after exercise.
• Passive cooldowns promote greater glycogen resynthesis.
• Glycogen resynthesis principles should be considered for athletes in tournaments or training.

Determining Exercise Progression

• Exercise frequency, intensity, or duration should increase gradually (no more than 10% each week for athletes).
• At higher fitness levels, incrementing frequency or duration of workouts is less feasible.
• Progress in training occurs through intensity manipulation whenever increasing either volume or duration is not feasible.

Examples of Aerobic Exercise Progression

• Example exercise sessions demonstrate volume load then intensity.
• Example workouts are suggestive and should be customized to individual ability.

Determining Frequency (Considerations)

• Frequency of training (~5 times per week) may be useful for an athlete.
• Dose response to exercise training is beneficial (training intensity, duration and frequency).
• More training sessions are beneficial for lower intensity exercise or exercise with shorter durations if intensity/duration are not changed.

Interaction Among Intensity, Frequency, and Duration

• Aerobic training adaptations are more likely correlated with workout intensity and total work accomplished than the exercise sequence.
• Adjusting frequency and duration depending on the workout intensity is helpful when total workout work is to be kept the same.
• Adjusting workout duration and frequency can work interchangeably.

Determining Exercise Progression

• Exercise frequency, intensity, or duration should not increase by more than 10% every week.
• At higher fitness levels, reaching a plateau in increasing frequency or duration will mean progression must proceed by increasing workout intensity.

Physiological Differences (HR vs. Lactate Threshold)

• HR method: intensity based on the cardiovascular stress.
• Lactate threshold method: intensity based on metabolic stress.
• A given intensity level of stress in one system doesn't guarantee the same level of stress in another system.

Which HR Method to Use

• Use percentages of current maximum capabilities to determine intensity, like %VO2max or %HRreserve.
• Use the HR method that most accurately reflects the desired work intensity and level
• Best is to determine a specific HR associated with a specific %VO2max.

Test your knowledge on the Krebs Cycle, electron transport chain, and principles of exercise physiology. This quiz covers key concepts including ATP production, fatty acid oxidation, and effective training strategies. Perfect for students and fitness enthusiasts looking to deepen their understanding of these biological processes.