Notes on Muscle Fibers and Training Physiology

Overview of Muscle Fibers

• Muscle fibers are categorized into two main types based on their characteristics and function:
  • Red Muscle Fibers: Known as Type I fibers/Aerobic fibers
  • Rich in myoglobin and hemoglobin, which gives them a darker color
  • More vascularized with a rich blood supply
  • Specialized for endurance activities
  • These fibers split ATP slowly and resist fatigue
  • White Muscle Fibers: Known as Type II fibers/Anaerobic fibers
  • Less vascularized
  • Specialized for short bursts of power and speed
  • These fibers split ATP quickly and fatigue easily

Physiological Differences in Muscle Fiber Types

• Red (Type I) vs. White (Type II):
  • Red muscle fibers contain more iron and myoglobin for oxygen storage, allowing for aerobic respiration.
  • White muscle fibers are adapted for anaerobic conditions, leading to the production of lactic acid during exertion.
  • The color difference primarily stems from blood supply and oxygen content.

Activation of Muscle Fibers

• Type I fibers are recruited first for aerobic activities, while Type II fibers are utilized during anaerobic activities.
• Lactic acid is produced when the body switches to anaerobic metabolism, particularly in high-intensity activities.

Considerations in Exercise

• Athletes predominantly utilize aerobic respiration (Type I fibers) for long-distance activities and switch to anaerobic (Type II fibers) for short sprints or heavy weightlifting.
• Energy System Overview:
  • Glycolysis leads to the production of pyruvate, which can either undergo aerobic metabolism (making acetyl CoA) or anaerobic metabolism (forming lactate).

Heart Rate and Exercise Intensity

• Maximum Heart Rate (MHR): Depending on age, crucial for determining training zones. Calculated as 220 - age (for males) or 225 - age (for females).
• Exercise in heart rate zones:
  • 60-70% MHR: Primarily aerobic; can sustain for longer periods.
  • Above 70% MHR: Approaches anaerobic threshold where lactic acid accumulation begins.

Heart Rate Reserve Approach

• Training intensity is regulated not just by MHR but by Heart Rate Reserve (HRR):
  • Calculated as MHR - Resting Heart Rate
  • Training Heart Rate =
  • HRR * %Intended Intensity + Resting Heart Rate
• This formula accommodates individual cardiovascular fitness levels, providing a more personalized training zone.

Practical Application in Training

• To enhance performance:
  • Spend time training within the Lactate Threshold Zone (80-85% MHR) to improve speed and power.
  • Regular aerobic workouts improve overall fitness, endurance, and health.

Additional Considerations

• The decline in maximum heart rate with age varies among individuals based on their level of fitness and activity.
• Ongoing assessments and induced maximum heart rate testing are suggested for personalized training outcomes.
• Keep in mind the significance of aerobic vs. anaerobic activity for efficient training and performance strategies.