What is exercise physiology?

Exercise Physiology Basics

  • Exercise Physiology: Study of skeletal muscle contractions and their effects.

  • Definitions:

    • Physical Activity: Movement by skeletal muscles leading to energy expenditure.

    • Exercise: Structured physical activity.

Muscle Types & Skeletal Muscle Characteristics

  • Types of Muscle: Skeletal, smooth, and cardiac.

  • Skeletal Muscle:

    • Makes up 40-50% of body weight.

    • Long, multinucleated fibers, striated, voluntary control.

Skeletal Muscle Structure

  • Layers:

    • Epimysium (muscle), perimysium (fascicles), endomysium (fibers), sarcolemma (membrane).

  • Components:

    • Myofibrils → Sarcomeres → Actin (thin) and Myosin (thick) filaments.

    • Sarcomeres are the functional contraction unit.

Key Organelles in Muscle Fibers

  • Myofibrils: Contain actin and myosin.

  • T-tubules: Conduct impulses, triggering calcium release.

  • Sarcoplasmic Reticulum (SR): Calcium storage.

  • Mitochondria: Aerobic metabolism.

Muscle Contraction

  • Sliding Filament Theory:

    • Actin slides over myosin, shortening sarcomeres.

    • Myosin heads bind to actin and ATP, performing power strokes.

  • Neuromuscular Junction:

    • Acetylcholine (ACh) triggers muscle action potential.

    • Calcium released from SR binds to troponin, moving tropomyosin to expose actin binding sites.

End of Contraction

  • Calcium is pumped back into SR.

  • Troponin and tropomyosin return to resting positions, blocking myosin binding.

Muscle Fiber Types

  • Type I (Slow-Twitch):

    • Small diameter, high oxidative capacity, fatigue-resistant, endurance activities.

  • Type II (Fast-Twitch):

    • Large diameter, high peak force, fatigue quickly, for sprints and high-power activities.

    • Subtypes: IIa (moderate endurance) and IIx (low endurance).

Types of Muscle Contraction

  • By Length:

    • Concentric (shortens), Isometric (no change), Eccentric (lengthens).

  • By Force/Velocity:

    • Isotonic (variable velocity), Isokinetic (constant velocity), Isometric (no velocity).

Key Relationships

  • Length-Tension Relationship: Optimal length for maximum force production.

  • Force-Velocity Relationship: As velocity increases, force decreases.

Delayed Onset Muscle Soreness (DOMS)

  • Caused by eccentric exercise.

  • Symptoms appear 1-3 days post-exercise, often in untrained individuals.