Fast Slow and Intermediate Fibers

Power: Maximum amount of tension that can be produced by a muscle Depends on number of contractile units which depends on muscle size Endurance: The maximum number of times a muscle can repeat an activity Depends on the aerobic ability of the muscle

Both power and endurance are influenced by types of muscle fiber in the muscle and the training and condition of the muscle

Types of Muscle Fibers Fast (fast twitch) Fibers Large in diameter, dense myofibrils, few mitochondria, few blood vessels Contract hard, mostly use anaerobic pathways for energy, fatigue quickly. Example: White meat on turkey or chicken breast (pectoral muscles used for flight)

Slow Fibers ½ the diameter of fast fibers Contract 3x slower than fast fibers Have many mitochondria Have a greater blood supply Example: Dark meat of a turkey or chicken

Intermediate fibers: In between in size. Most adaptable. Most human muscles are a mixture of types Ratio of fast vs slow seems to be genetically determined

To Build Power: You need large diameter fibers with more actin and myosin proteins You need more protein in the diet You need to do exercises with fewer repetitions Use heavier resistance. Work at higher speed (sprints). Recovery time is needed for muscle repair

To Build Endurance: You want the muscle to have more blood vessels and more mitochondria Do many repetitions with lighter weight Take in a balanced diet with adequate carbohydrates. Exercises that improve heart and lung function also are needed. The best exercise for most is a combination of both strength training and aerobic type exercises.