Hypertrophy is an increase in muscle mass due to the addition of structural proteins. The opposite of hypertrophy is atrophy, the loss of muscle mass due to the breakdown of structural proteins. Endurance exercise causes an increase in cellular mitochondria, myoglobin, and capillary networks in SO fibers. Endurance athletes have a high level of SO fibers relative to the other fiber types. Resistance exercise causes hypertrophy. Power-producing muscles have a higher number of FG fibers than of slow fibers. Strenuous exercise causes muscle cell damage that requires time to heal. Some athletes use performance-enhancing substances to enhance muscle performance. Muscle atrophy due to age is called sarcopenia and occurs as muscle fibers die and are replaced by connective and adipose tissue.
angiogenesis
formation of blood capillary networks
atrophy
loss of structural proteins from muscle fibers
hypertrophy
addition of structural proteins to muscle fibers
sarcopenia
age-related muscle atrophy
1. The muscles of a professional sprinter are most likely to have ________.
A) 80 percent fast-twitch muscle fibers and 20 percent slow-twitch muscle fibers
B) 20 percent fast-twitch muscle fibers and 80 percent slow-twitch muscle fibers
C) 50 percent fast-twitch muscle fibers and 50 percent slow-twitch muscle fibers
D) 40 percent fast-twitch muscle fibers and 60 percent slow-twitch muscle fibers
A
2. The muscles of a professional marathon runner are most likely to have ________.
A) 80 percent fast-twitch muscle fibers and 20 percent slow-twitch muscle fibers
B) 20 percent fast-twitch muscle fibers and 80 percent slow-twitch muscle fibers
C) 50 percent fast-twitch muscle fibers and 50 percent slow-twitch muscle fibers
D) 40 percent fast-twitch muscle fibers and 60 percent slow-twitch muscle fibers
B
3. Which of the following statements is true?
A) Fast fibers have a small diameter.
B) Fast fibers contain loosely packed myofibrils.
C) Fast fibers have large glycogen reserves.
D) Fast fibers have many mitochondria.
C
4. Which of the following statements is false?
A) Slow fibers have a small network of capillaries.
B) Slow fibers contain the pigment myoglobin.
C) Slow fibers contain a large number of mitochondria.
D) Slow fibers contract for extended periods.
A
1. What changes occur at the cellular level in response to endurance training?
Endurance training modifies slow fibers to make them more efficient by producing more mitochondria to enable more aerobic metabolism and more ATP production. Endurance exercise can also increase the amount of myoglobin in a cell and formation of more extensive capillary networks around the fiber.
2. What changes occur at the cellular level in response to resistance training?
Resistance exercises affect muscles by causing the formation of more actin and myosin, increasing the structure of muscle fibers.