Detailed Study Notes on Muscle Actions and Training

Eccentric and Concentric Muscle Actions

  • Definitions:

    • Eccentric Muscle Action: Muscle fibers lengthen while producing force.
    • Concentric Muscle Action: Muscle fibers shorten while producing force.

  • Examples of Muscle Actions:

    • Bicep Curl:
    • Going from full extension to full flexion (concentric).
    • Lowering the weight involves controlling the descent (eccentric).

  • Strength Differences:

    • Greater force production during eccentric actions due to actin and myosin binding being stretched apart rather than contracted.

Muscle Soreness and Hypertrophy

  • Delayed Onset Muscle Soreness (DOMS):
    • Occurs 24-48 hours post-exercise, especially after unaccustomed eccentric activity.
  • Hypertrophy vs. Hyperplasia:
    • Hypertrophy: Increase in muscle fiber size.
    • Hyperplasia: Increase in the number of muscle fibers, more common in laboratory animals than in humans.

Metabolic Adaptations to Training

  • ATP Production and Training:
    • Endurance training enhances mitochondria and energy pathways.
    • Resistance training leads to specific adaptions such as increases in storage of creatine phosphate (up to 45%).
  • Glycolytic Enzymes:
    • Changes depend on the type of training; typical low-repetition workouts may not enhance glycolytic enzymes due to less demand.

Types of Strength Testing

  • Isometric Strength:

    • Specific to joint angle; force production relates to actin-myosin overlap.
    • Optimal overlap produces maximum force, while too much overlap reduces force.

  • Isokinetic Testing:

    • Measures torque at various angles, providing a torque curve which is beneficial for tracking strength across the range of motion.

Torque-Velocity Relationship

  • General Curve:

    • Eccentric muscle action typically produces higher torque than concentric at various velocities.
    • As speed increases, concentric strength tends to decrease (decay curve).

  • Eccentric Torque Behavior:

    • Increased torque production with velocity until certain limit, where the actin-myosin binding becomes less effective.

Practical Applications

  • In resistance training, vary the type of muscle actions to address muscle hypertrophy and maximize strength benefits.
  • Understanding how muscle actions work can guide exercise programming for better results and prevention of injuries.