6+Biomechanic.s+of+Human+Muscle+--+professor

Biomechanics of Human Skeletal Muscle

Behavioral Properties of Musculotendinous Unit

  • Extensibility: Ability of muscle tissue to be stretched without damage.

  • Contractility: Ability of muscle to contract and generate force.

  • Elasticity: Ability to return to original shape after stretching.

  • Excitability: Responsiveness to stimuli.

  • Irritability: Similar to excitability; the capacity to respond to physical stimulus.

  • Adaptability: Ability to change with training or different conditions.

Two Components to a Muscle

  • Contractile Component: Responsible for muscle contraction.

  • Non-Contractile Components: Provides support and structure; includes:

    • Parallel Elastic Component: Passive elasticity of muscle membranes.

    • Series Elastic Component: Elasticity derived from tendons; contributes to force generation during muscle contraction.

Muscle Contraction Types

  • Isometric Contraction: Muscle length remains constant while generating force.

  • Isotonic Contraction: Muscle changes length while generating force:

    • Concentric: Muscle shortens while contracting.

    • Eccentric: Muscle lengthens while contracting under load.

Review of Muscle Makeup

  • Components:

    • Tendon: Connective tissue attaching muscle to bone.

    • Fascia: Surrounds muscles, providing structure and support.

    • Whole Muscle: Composed of muscle fibers.

    • Muscle Fiber (Cells): Individual muscle cells.

    • Sarcolemma: Membrane surrounding muscle fibers.

    • Myofibrils: Strands within muscle fibers containing contractile proteins.

    • Myofilaments: Actin (thin) and Myosin (thick) filaments forming muscle striations.

Gross Structure of Muscle Contractile Component

  • Macroscopic Level:

    • Entire muscle encased in epimysium.

    • Bundles of muscle fibers encased in perimysium.

    • Each muscle fiber consists of bundles of myofibrils encased in endomysium where sarcomeres are located.

Biomechanics of Skeletal Muscle

  • Muscle fibers vary in length; some run the entire muscle length while others are shorter.

  • Two types of arrangements:

    • Parallel (Fusiform): Long fibers, fewer fibers per cross-section, faster shortening speeds.

    • Pennate: Short fibers attach to tendons; can be unipennate, bipennate, or multipennate, providing more force but slower speeds.

  • Growth: Fibers increase in length and diameter from birth through adulthood; resistance training increases diameter.

  • Hypertrophy vs Hyperplasia: Hypertrophy refers to fiber size increase, while hyperplasia involves an increase in the number of fibers.

Biomechanics of Muscle Fiber Orientation

  • Parallel Fiber Arrangements:

    • Fibers run parallel to muscle's longitudinal axis.

    • Advantages: Fast movements, larger range of motion (ROM).

    • Disadvantages: Less force production.

  • Pennate Muscle Fiber Arrangement:

    • Fibers are shorter and attach to a tendon.

    • Provides more force than parallel arrangements but has a reduced range of motion and slower speeds.

  • Triangular (Convergent) Fiber Arrangement:

    • Covers broad area with fibers converging to a single tendon.

  • Quadrate Fiber Arrangement:

    • More rectangular shape; examples include the Quadratus Femoris that connects the ischium to the femur.

Biomechanics of Pennated Muscles: A Closer Look

  • Angle of Pennation (PA): Changes with contraction; smaller angles result in greater force production but may hinder shortening speed.

  • Study findings: Bodybuilders had greater strength and pennation angles associated with lower force per cross-sectional area.

Muscle Fiber Characteristics

  • Slow-Twitch Fibers (Type I): Slow to contract, resistant to fatigue, high mitochondrial concentration for aerobic energy.

  • Fast-Twitch Fibers (Type IIA and IIB):

    • Type IIA: Intermediate contraction speed and force.

    • Type IIB: Fast contraction, high force production, and fatigue quickly.

Non-Contractile Components of Muscle

  • Parallel Elastic Component: Provides passive elasticity from muscle membranes.

  • Series Elastic Component: Derived from tendon elasticity aiding force production.

Mechanical Properties of Tendon

  • Toe Region: Initial stretch with nonlinear response (up to 2% strain).

  • Elastic Region: Up to 4% strain; tendon returns to original length.

  • Plastic Region: Beyond 8-10% strain; begins microscopic failure.

Quantitative Assessment of Muscular Activity: Electromyography (EMG)

  • EMG: Technique to record and analyze myoelectric signals and assess muscle activation.

  • Signal Influences:

    • Recruitment levels, muscle depth, contraction type, electrode placement, and psychological factors.

Measuring Muscle Force

  • Qualitative Methods: Hand-held dynamometers, isokinetic devices.

  • Isokinetic Strength Testing: Measures muscle contraction speed throughout the range of motion.

  • Maximum Torque Calculation: Key for assessing muscular strength; involves 1 Repetition Maximum (1RM) and Maximal Voluntary Contraction (MVC).

Muscular Endurance

  • Ability of muscle to exert tension over time; characterized as opposite of muscle fatigability.

Effects of Muscle Temperature and Warm-up Prior to Competition

  • Increased temperature enhances nerve and muscle function speeds, impacting the force-velocity curve positively.

Jumping Experiment Analysis

  • Includes Squat Jump, Counter Movement Jump, and Drop Jump, focusing on the mechanics of jump height and muscle force development.