The Human Heart and Exercise

Jun 20, 2024

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The Human Heart and Exercise: Lecture Notes

Introduction

  • Video Sponsor: Athletic Greens (link in description).
  • Topic: Human heart, its functions, and its response to exercise.

The Human Heart

  • Weight: 8-10 ounces.
  • Function: Pumps blood throughout the body.
  • Beat Frequency: ~100,000 times/day, ~35 million times/year, ~2.5 billion times/lifetime.

Heart Anatomy and Function

  • Main Job: Pump blood to body tissues, focusing on muscle tissue during exercise.
  • Key Structures: Left Ventricle, Aorta
    • Left Ventricle: Most powerful, thick muscular wall, pumps blood to entire body through the aorta.
    • Aorta: Largest artery, elastic recoil, large size, branches out to other arteries to distribute blood.

Blood Flow to Muscles During Exercise

  • Example: Quadriceps (thigh muscles)
  • Blood Flow Path:
    • Arteries → Arterioles → Capillaries (oxygen diffusion) → Venules → Veins (deoxygenated blood back to heart).
  • Key Chambers: Right atrium (receives deoxygenated blood) → Right ventricle (pumps to lungs) → Left atrium → Left ventricle → Aorta.
  • Quiz Question: Name all four heart valves (comment answer).

Changes in Blood Flow During Exercise

  • Resting Muscle: 3-4 ml/min per 100g of muscle tissue.
  • Exercising Muscle: Up to 200 ml/min per 100g for average, up to 400 ml/min for elite athletes.
  • Circulatory Adjustments:
    1. Increase in cardiac output.
    2. Vasoconstriction of peripheral arterioles.
    3. Forceful contraction of vein walls.

1. Increase in Cardiac Output

  • Definition: Amount of blood pumped by the heart per minute.
  • Influencing Factors:
    • Heart Rate (beats per minute).
    • Stroke Volume (blood volume per beat).
  • Exercise Response:
    • Heart rate can reach up to ~200 bpm.
    • Stroke volume increases due to stronger left ventricle contractions.
  • Cardiac Output Numbers:
    • At rest: ~5 liters/min.
    • Untrained individuals during exercise: 13-15 liters/min.
    • Elite athletes: 30-40 liters/min.

2. Vasoconstriction of Peripheral Arterioles

  • Purpose: Redirect blood flow to exercising muscles.
  • Mechanism: Constriction in non-muscular tissues (e.g., intestines) while leaving muscle and essential areas (brain, heart) open.

3. Forceful Contraction of Vein Walls

  • Mechanism: Increases venous return, enhancing blood flow back to the heart.
  • Related Concept: Frank-Starling Law - heart muscle contracts more forcefully with increased blood volume.

Long-term Cardiac Adaptations

  • Myocardial Mass: Can increase by 50-75% in elite athletes (hypertrophy of cardiac muscle cells).
  • Stroke Volume Increase: More efficient blood pumping per beat.
  • Resting Heart Rate: Decreases in trained individuals.
  • Microvascularization: Increased number of capillaries in muscle tissue, enhancing oxygen delivery.

Summary

  • Amazing Heart Adaptations: Occur with consistent exercise, making heart stronger and more efficient.
  • Next Topics: Muscular adaptations to exercise (future videos).

Sponsor: Athletic Greens

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  • Usage: 1 scoop in 8 oz. of water; enhances energy levels and recovery between workouts.
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Conclusion

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