Week 1 (Myofibers & Muscle Fiber Types)

Myofiber = a muscle cell

  • Functions to produce force and heat

Diameter & Length

  • Diameter - Varies on age, genetics, nutrition, diseases, training

    • Primary factor affecting maximal force production of the cell

    • Bigger diameter = bigger force

  • Length - Varies on age, genetics, and specific skeletal muscle

    • Affects the maximal speed of shortening, concentric contraction force & degree of muscle length change

    • Comparing Absolute Length to length change in different muscle fibers

      • 1) Higher absolute length = higher possibility of length change

      • 2) Higher vmax or higher velocity/speed

      • 3) Higher absolute length = higher concentric/contraction force produced

      • 4) ATP use

    • The sarcomere 



Myosin is heavily important for the force or movement of the muscle fibers

Different types of Muscle Fibers

Type I (occurs/performs slowly)

  • Color is typically really red when healthy

  • Slow contraction/

  • Myosin heavy chain (MHC)

  • MHC type I

  • High Mitochondria

  • High in Myoglobin

  • High Capillaries/capillary density

  • Low in Glycolytic enzymes/glycogen

Type IIa (occurs/performs moderately)

  • Intermediate contraction

  • MHC type IIa

  • High Mitochondria

  • High in Myoglobin

  • High in Capillaries/capillary density

  • High in Glycolytic enzymes/glycogen

Type IIx (occurs/performs fast)

  • MHCII type IIx

  • Fastest type

  • Low Mitochondria

  • Low in Myoglobin

  • Low Capillaries/capillary density

  • High Glycolytic enzymes/glycogen



Energy 

  • Mitochondria (oxidative enzyme)

  • Myoglobin

  • Capillaries

  • Glycolytic enzymes/ Glycogen