9.5 Types of Skeletal Muscle Fibers

• Major types of skeletal muscle fibers: fast, slow, intermediate
• Fast fibers or white fibers
• Fast fibers are large in diameter
• Fast fibers are densely packed myofibrils
• Fast fibers have large glycogen reserves
• Fast fibers have relatively few mitochondria
• Fast reaction uses a lot of ATP but there is often not enough
• Contractions for fast fibers are primarily supported by anaerobic metabolism
• Glycolysis in fast fibers does not require oxygen and converts to lactic acid
• Slow fibers or red fibers
• Slow fibers are small in diameter
• Small fibers take long to contract
• Slow fibers are meant for extended periods and fatigue slowly
• Aerobic metabolism in slow fibers
• Aerobic metabolism comes from either a larger network with greater blood flow or myoglobin
• Myoglobin is a red pigment, binds oxygen molecules
• Intermediate fibers are in between properties and characteristics
• Amount of muscle percentages between fast, slow, and intermediate varies by person
• Why does a sprinter experience muscle fatigue after a few minutes, when it takes a marathon runner hours?

  A sprinter usually runs in bursts, best with anaerobic metabolism. Marathon runners go long distance which is best with aerobic metabolism