03/27

Aerobic vs Anaerobic Metabolism

• Aerobic Metabolism:

  • Involves ATP synthesis using oxygen in the mitochondria.

  • Provides ATP for longer durations, utilizing slow-twitch (type I) muscle fibers.

  • Aerobic metabolism leads to sustainable energy production but lower concentrations of ATP output per molecule of glucose compared to anaerobic mechanisms.

• Anaerobic Metabolism:

  • ATP synthesis occurs without oxygen, primarily in cytoplasm.

  • Produces ATP much quicker than aerobic metabolism but only for short bursts of high-intensity efforts, resulting in lactate build-up.

Performance Concepts

• Elements that affect performance discussed include metabolic adaptations, muscle fiber types, and hormonal response during exercises.

• Focused on the effects of aerobic training on enhancing performance. Examples include increased endurance and adaptations to the cardiovascular system.

Energy Sources During Exercise

• Initial seconds of high-intensity effort are primarily anaerobic using ATP-PC system, transitioning to glycolysis, and subsequently to aerobic sources as oxygen becomes sufficient.

• Delay of oxygen supply during the start of workouts causes reliance on anaerobic metabolism despite aerobic demands.

Determinants of Aerobic Performance

• Key factors influencing aerobic performance:

1. VO2 Max:

   • Measures aerobic capacity and serves as a predictor of endurance performance.

2. Fiber Type Distribution:

   • Predominantly influences the energy production methods a body can utilize effectively.

3. Lactate Threshold:

   • Point at which lactate starts to accumulate in the blood, indicating a switch towards anaerobic metabolism.

Cardiac Output Explanation

• Cardiac Output (CO) = Heart Rate (HR) x Stroke Volume (SV)

• Stroke volume consists of EDV and ESV:

  • EDV = total blood volume in the ventricle at the end of diastole; more volume leads to greater stroke volume.

  • ESV = blood volume left in the ventricle at the end of systole; lower ESV is better for efficient heart functioning.

Frank-Starling Mechanism

• Increased EDV enhances cardiac output as it leads to stronger contractions due to increased stretch of heart muscle fibers.

• Significance of preload (EDV) and afterload (resistances heart faces during contraction) discussed.

Understanding Afterload

• Afterload is defined as the resistance the heart's left ventricle encounters while pumping blood into the aorta.

• It is closely linked to blood pressure; higher blood pressure means greater resistance against which the heart must work.

Impact of Afterload on Stroke Volume

• An increase in afterload leads to a decrease in stroke volume, resulting in reduced blood ejected per heartbeat.

• Inverse relationship:

• More afterload = less stroke volume

Factors Influencing Stroke Volume

• Three primary factors include:

• Contractility - Strength of heart contractions

• Preload - Initial stretching of the ventricles

• Afterload - Resistance faced by the heart

• Afterload is the only factor exhibiting an inverse relationship with stroke volume among these three.

Relation with Cardiac Output

• Cardiac output (CO) = Stroke volume (SV) × Heart rate (HR)

• Increasing heart rate generally increases cardiac output, but this has limits.

Ejection Fraction

• Defined as the volume of blood pumped out of the ventricles with each heartbeat.

• Higher ejection fraction is desirable, especially for athletes.

• Factors leading to higher ejection fractions:

• Increased contractility

• Lower aortic pressure

• Longer filling times (increased preload)

Contractility and Ejection Fraction

• Increased contractility leads to a higher ejection fraction.

• Factors influencing contractility:

• Preload effect: more stretch leads to a stronger contraction (Frank-Starling mechanism).

• Hormonal influences (e.g., adrenaline) and sympathetic nervous system activation

Role of Heart Rate

• Heart rate affects diastolic filling time; slower heart rates can allow for increased preload and stretch of the ventricles.

• Increased heart rate can lead to decreased filling time unless trained for efficiency.

Venous Return Factors

• Factors affecting venous return include:

• Skeletal Muscle Pump - Muscle contractions aid blood flow back to the heart.

• Respiratory Pump - Pressure changes during breathing facilitate blood movement.

• Vein Constriction - Constriction of the veins assists in directing blood flow towards the heart.

Cardiovascular Differences Between Athletes and Non-Athletes

• Trained athletes often have lower resting heart rates and higher stroke volumes compared to untrained individuals.

• During maximal exercise, athletes exhibit significant differences in cardiac output due to higher stroke volume and lower heart rates.

Final Notes

• Understanding the relationships between preload, afterload, stroke volume, and cardiac output is essential in physiology and medical studies.

• Emphasizing the need for further training can enhance overall cardiac efficiency and performance in athletes.

• Key takeaways include:

• Afterload is the sole factor decreasing stroke volume.

• Ejection fraction can be optimized through various methods: increasing contractility, reducing afterload, and allowing longer filling time.

• Understanding these physiological concepts is crucial for applying knowledge in clinical or athletic settings.