2/17 exercise phys

Lab Schedule and Preparation

• Labs begin this week:

  • February 30: 2:30 PM

  • Tomorrow: 7:00 PM

  • Wednesday: 2:30 PM

• Location: Room 130, down the hall

• Preparation for Lab:

  • Read pages 170-177 from the lab book before attending.

  • Initial lecture will be about 30 minutes focusing on theory.

• Exam Information:

  • First lecture exam on March 5.

  • Format will include fill-in-the-blank and listing questions.

• Example of fill-in-the-blank question: "A ___ is the connective tissue sheath that surrounds ___.”

Muscle Fiber Types

• Recap from last discussion focused on how neurons dictate muscle fiber traits.

  • Neurons communicate with muscle fibers via:

    • Use-Disuse Theory: Adaptive theory explains how unidentified substances produced in low motor neurons influence fiber traits.

    • Axoplasmic Flow Theory: Involves chemical messenger systems that instruct fibers on traits.

• Staining Methods:

  • Staining for ATPase indicates speed of contraction.

  • Dark stain for ATPase indicates fast-twitch fibers; dark stain for SDH indicates oxidative (slow-twitch) fibers.

Fiber Type Distribution Patterns

• Definitions: Fiber type distribution refers to the percentage of various fiber types within muscles and individuals relevant to performance in exercise and sports.

• Sex Comparisons:

  • General consensus shows no significant differences in fiber type distribution patterns between men and women based on studies.

  • Muscle type varies significantly among different muscles within the same individual.

• Examples of Muscle Fiber Types:

  • Vastus Lateralis and Rectus Femoris: 50% slow-twitch and 50% fast-twitch, enabling both endurance and explosive activities.

  • Soleus Muscle: Approximately 90% slow-twitch, primarily for postural stability and endurance tasks.

Athletic Performance and Fiber Types

• Challenges in Characterizing Athletes Based on Fiber Types:

  • Athletes possess different fiber type distributions depending on their specific muscles (e.g., a distance runner vs. sprinter).

  • Overall muscle utilization affects performance more than dominant fiber types.

• Examples of Distribution Variability:

  • Elite marathoners can exhibit 82-83% slow-twitch fibers but can also include individuals with lower slow-twitch percentages.

  • Sprinters often present over 60% fast-twitch fibers, with variability among individuals.

Implications of Genetics on Fiber Types

• Fiber type distribution is genetically determined; training has minimal impact on converting fast-twitch to slow-twitch fibers and vice versa.

• Training and Performance:

  • Strong genetic predispositions determine effectiveness in various sports:

    • Endurance athletes excel with higher slow-twitch fibers.

    • Sprinters/jumpers similarly require high fast-twitch fibers for optimum performance.

Factors Affecting Force Production in Muscles

• Key factors influencing muscle force production include:

  1. Number of Activated Motor Units: More activated units correspond to higher force.

  2. Number of Muscle Fibers Within Motor Units: Larger fiber numbers lead to greater overall force.

  3. Muscle Fiber Size: Larger fibers generally produce more force.

  4. Velocity of Contraction: Strength varies with contraction speed; individuals are generally stronger at slower speeds.

Neural Factors in Force Production

• Understanding how stimulation and inhibition control force production:

  • Acetylcholine (ACH): Released as a stimulatory neurotransmitter at the junction of upper and lower motor neurons.

  • Gamma-Aminobutyric Acid (GABA): Functions as an inhibitory neurotransmitter, balancing muscle activation.

• Neural Adaptations: In early phases of resistance training:

  • Subjects may experience increased strength without changes in muscle size due to increased motor unit activation.