KJ

Muscle Anatomy and Function

Muscle Groups and Functions

  • Agonist (Prime Mover)

    • Performs the primary action during movement.

    • Example: During flexion, the bicep brachial contracts (shortens).

  • Antagonist

    • Opposes the agonist and relaxes during the movement.

    • Example: When the bicep contracts, the tricep brachial stretches (lengthens) and acts as the antagonist.

  • Synergists

    • Assist the prime mover to enhance the movement (e.g., brachialis, coracobrachialis, brachioradialis).

    • Help distribute the workload to prevent fatigue.

  • Fixators

    • Stabilize the joint so the prime mover can function without interference.

Muscle Movements

  • Types of Movements

    • Flexion: Bending a joint (decreasing the angle).

    • Extension: Straightening a joint (increasing the angle).

    • Example: During arm flexion, the bicep is the agonist and the tricep is the antagonist;

    • During arm extension, the roles are reversed.

Muscle Anatomy and Mechanics

  • Muscle Origin and Insertion

    • Origin: More stable attachment point of the muscle.

    • Insertion: Moves towards the origin when the muscle contracts.

    • A muscle is connected to the bone via a tendon.

  • Motor Unit

    • Composed of a motor neuron and the muscle fibers it innervates.

    • Recruitment of motor units occurs based on the weight (tension) being lifted.

Muscle Fiber Types

  • Fast Twitch Fibers

    • Burn ATP rapidly; suited for explosive movements.

    • E.g., football linemen who expend energy in short bursts.

  • Slow Twitch Fibers

    • Burn ATP slowly; suited for endurance activities.

    • Bright red color due to high myoglobin and mitochondrial content. Example: marathon runners.

  • Oxygen Debt

    • The amount of oxygen required to metabolize lactate produced during anaerobic respiration post-exercise.

    • Key for recovery after intense physical activity.

Muscle Adaptation

  • Hypertrophy: Increase in muscle size due to increased workload (mechanical stress).

  • Atrophy: Decrease in muscle size due to disuse or nerve damage.

    • Disuse Atrophy: Caused by immobilization (e.g., arm in a cast).

    • Denervation Atrophy: Caused by nerve damage leading to muscle wastage.

Muscle Structure

  • Muscles of the Face

    • Numerous muscles allow for diverse facial expressions.

    • Example: Zygomaticus major for smiling and depressor anguli oris for frowning.

  • Core Muscles

    • Rectus Abdominis: Flexes the spine (six-pack muscle).

    • Transverse Abdominis: Stabilizes the core.

    • Obliques (internal and external): Allow for twisting movements.

Specific Muscle Groups

  • Quadriceps: Group of four muscles responsible for knee extension.

    • Includes rectus femoris, vastus lateralis, vastus medialis, and vastus intermedius.

  • Hamstrings: A group of three muscles located at the back of the thigh responsible for knee flexion.

  • Gluteal Muscles: Include gluteus maximus, gluteus medius, and gluteus minimus, responsible for hip movements.

  • Gastrocnemius: Calf muscle that facilitates plantarflexion of the foot.

    • Attached to the calcaneus via the Achilles tendon (calcaneal tendon).

Stretching and Flexibility

  • Important for preventing muscle stiffness and maintaining a full range of motion.

  • Recommends stretching post-workout to avoid stiffness due to tightness in muscles post-exercise.

Conclusion

  • Understanding muscle anatomy and function enhances knowledge of how muscles work together in movements and their adaptations.