Question

All of the following may happen in response to exercise training except: a. increase in the number of myofibrils b. increase in the storage of glycogen and creatine phosphate c. increase in the number of muscle fibers d. increase in the number of mitochondria

Short answer

c. increase in the number of muscle fibers

Step-by-step solution

Understand the context

Exercise training typically leads to various physiological adaptations in the muscles, such as changes in the structure and function to accommodate increased activity.

Analyze each option

Go through each option to determine which can happen due to exercise training: (a) Increase in the number of myofibrils - Exercise can lead to hypertrophy, increasing the number of myofibrils. (b) Increase in the storage of glycogen and creatine phosphate - These are energy sources stored in the muscles, and their storage increases to meet higher energy demands. (c) Increase in the number of muscle fibers - The increase in muscle size after training is usually due to hypertrophy (growth of existing fibers), not an increase in the number of fibers. (d) Increase in the number of mitochondria - To meet higher energy demands, the number of mitochondria in muscle cells usually increases.

Identify the correct answer

The option that does not typically happen in response to exercise training is: (c) Increase in the number of muscle fibers. Muscle growth primarily happens through hypertrophy, which increases the size of existing fibers rather than increasing their number.

Key concepts

Muscle Hypertrophy

Muscle hypertrophy refers to the growth and increase in the size of muscle cells. This process mainly happens through resistance training and exercise. When we lift weights or perform high-intensity workouts, small tears are created in the muscle fibers. The body then repairs these tears by fusing muscle fibers together to form new strands of protein. This repair process leads to an increase in the size and strength of the muscles.

Muscle hypertrophy is not the result of an increase in the number of muscle fibers, but rather the enlargement of existing fibers.

Myofibrils

Myofibrils are the basic rod-like units within muscle cells that are responsible for muscle contraction. They are made up of repeated sections called sarcomeres, which are the functional units of muscle fiber. During exercise training, the number of myofibrils can increase, which is one reason why muscles get larger and stronger.

Increasing the number of myofibrils enhances the muscle's ability to generate force, which contributes to improved performance in both strength and endurance activities.

Muscle Fibers

Muscle fibers are the cells that make up muscles. They are long, cylindrical, and multinucleated. There are different types of muscle fibers, including slow-twitch (Type I) and fast-twitch (Type II) fibers. Slow-twitch fibers are more endurance-oriented, whereas fast-twitch fibers are designed for short bursts of power and speed.

It's important to note that exercise training typically increases the size of muscle fibers (hypertrophy) rather than increasing their number. This is a crucial distinction for understanding how muscles adapt to training.

Mitochondria

Mitochondria are the powerhouses of the cells. They are responsible for producing the energy required for muscle contractions through a process known as cellular respiration. During exercise training, the number of mitochondria in muscle cells often increases. This adaptation helps the muscles meet the higher energy demands that come with increased physical activity.

An increase in mitochondria enhances the muscle's aerobic capacity, allowing for better endurance and efficiency in energy production.

Energy Storage

Energy storage in muscles primarily involves glycogen and creatine phosphate. Glycogen is a stored form of glucose, which muscles use for energy during prolonged or intense exercise. Creatine phosphate is a molecule that provides quick bursts of energy by donating a phosphate group to ADP to form ATP, the primary energy carrier in cells.

Exercise training increases the muscles' storage capacity for both glycogen and creatine phosphate, enabling athletes to perform better and sustain longer periods of activity. This adaptation is crucial for both endurance and high-intensity sports.