Understanding VO2max and Aerobic Fitness

Nov 14, 2024

VO2max and Aerobic Fitness

Definition

  • VO2max: Maximal amount of oxygen consumed in one minute; measure of aerobic fitness.

Factors Influencing VO2max

  • VO2max = Heart Rate Max x Stroke Volume Max x Delta Arteriovenous Oxygen Content (Fick equation)
  • Exercise training cannot increase maximal heart rate.

Methods to Increase VO2max

  1. Increase Stroke Volume
    • Increases blood circulation per minute.
  2. Increase Arteriovenous Oxygen Difference
    • More blood circulated per minute.
    • Enhanced oxygen uptake by tissues.

Mechanisms of Exercise-Induced Changes

Stroke Volume Increase

  • Definition: Amount of blood leaving the heart per beat.
  • Cause: Heart enlargement due to aerobic exercise.
  • Types of Heart Growth:
    • Pathological Hypertrophy: Thickening of heart wall, potentially leading to heart failure.
    • Physiologic Hypertrophy: Healthy heart growth from exercise.
      • Myocardium grows in series (new contractile units extend cardiac myocytes).
      • Ventricle chamber enlarges, allowing more blood intake.
      • Some parallel growth thickens the myocardium.

Physiologic vs. Pathologic Hypertrophy

  • Key Difference: Chamber radius to wall thickness ratio remains balanced in physiological hypertrophy.
  • Example: Proportional growth in chamber size and wall thickness maintains functionality.

Adaptations from Physiologic Hypertrophy

  • Heart grows in size and in strength.
  • Increased capillary network ensuring adequate oxygen supply to myocardium.

Increasing Arteriovenous Oxygen Difference

  • Angiogenesis: Growth of new blood vessels.
    • Up to 60% more capillaries around skeletal muscle cells post-training.
  • Erythropoietin (EPO): Stimulates red blood cell production.
    • Increases blood oxygen-carrying capacity.
  • Effects on Oxygen Delivery:
    • More blood vessels = slower blood flow = more oxygen diffusion time.
    • Shorter diffusion distance for oxygen.
    • Increased mitochondria decrease intracellular oxygen content, enhancing gradient-driven oxygen uptake.

Conclusion

  • Exercise training enhances VO2max by:
    • Increasing stroke volume.
    • Increasing arteriovenous oxygen difference.
  • Results in higher oxygen consumption per minute.