Exercise Physiology Lecture Notes

Introduction

• Exercise increases the body's energy demand significantly from its resting state.
• At rest, the autonomic nervous system leans towards parasympathetic tone, reducing heart and respiratory rates.
• Exercise activates the sympathetic nervous system, integrating responses to maintain homeostasis and meet cellular metabolic demands.

Issues of Concern

• Cardiovascular disease remains prevalent despite advances in prevention and treatment.
• Top risk factors: hypercholesterolemia, hypertension, diabetes, obesity, and tobacco use.
• Lack of exercise exacerbates these risk factors; regular exercise reduces mortality rates.
• Exercise improves insulin sensitivity and helps manage diabetes.

Cellular Level

• Skeletal muscle is crucial for movement and metabolism.
• Sarcomere: Fundamental unit for contraction, composed of myosin (thick filaments) and actin (thin filaments).
  • Myosin interacts with actin and ATP.
  • Thin filaments: Actin, tropomyosin, and troponin complex (TnC, TnI, TnT).
• Muscle contraction regulated by calcium release and ATP-driven pumps.
• Sliding filament theory explains actin and myosin interaction for contraction.

Organ Systems Involved

Musculoskeletal System

• Muscle Fiber Types:
  • Type I: Slow-twitch, resistant to fatigue, high oxidative capacity (postural muscles).
  • Type IIa: Fast oxidative glycolytic, moderate fatigue resistance, used in power activities.
  • Type IIx: Fast glycolytic, rapid fatigue, used in high-intensity exercises.
  • Hybrid Fibers: Transition between types based on training.
• Muscle fibers adapt through hypertrophy and satellite cell activation.
• Bone Remodeling: Increases mineral density in response to mechanical load.

Cardiovascular System

• Supports increased oxygen demand during exercise.
• Adaptations: Increased cardiac output and capillary density, shunting blood to active muscles.
• Oxygen delivery enhanced by increased RBC production and younger RBCs showing better oxygen release.

Plasma

• Plasma volume expands post-exercise, enhancing performance and temperature regulation.

Respiratory System

• Increases pulmonary ventilation during exercise to meet increased CO2 and O2 demands.
• CO2 transported as bicarbonate, transported for exhalation after conversion back to CO2.

Endocrine System

• Hormones involved in cellular growth and repair:
  • Testosterone: Increases muscle protein synthesis.
  • Growth Hormone: Released in response to exercise, aids growth.
  • Insulin-like Growth Factors (IGFs): Stimulates protein synthesis and muscle repair.
  • Glucocorticoids: Regulate glucose metabolism and inflammation.
  • Catecholamines: Increase during exercise, enhancing heart rate and output.
  • Insulin: Exercise increases insulin sensitivity, improving glycemic control.

Skin

• Enhanced blood flow for thermoregulation during exercise.

Immune System

• Moderate exercise boosts immunity; intense exercise may temporarily impair it.

Mechanism

• ATP Hydrolysis: Provides energy for muscle contraction.
• Anaerobic Metabolism: Quick energy through substrate-level phosphorylation.
• Aerobic Metabolism: Sustained energy via oxidative phosphorylation, using fats and carbohydrates.

Related Testing

• Exercise capacity indicates cardiovascular and pulmonary function.
• VO2 and VO2 max measure oxygen consumption and aerobic capacity.
• Testing helps identify exercise limitations and underlying conditions.

Pathophysiology

• Individuals with normal capacity reach VO2 max; those with conditions may not.
• Exercise intolerance could stem from cardiopulmonary or muscular issues.

Clinical Significance

• Exercise physiology helps identify underlying diseases.
• Exercise testing can guide treatment and improve patient quality of life.