Problem 21 - Anatomy and Physiology of Animals

Question

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

Step-by-Step Solution

Answer

b. 20% fast-twitch, 80% slow-twitch muscle fibers

Step 1: Understanding Fast-Twitch and Slow-Twitch Fibers

Fast-twitch fibers provide short bursts of strength or speed and fatigue quickly, making them better suited for short, high-intensity activities like sprinting. Slow-twitch fibers are more efficient at using oxygen to generate more fuel for extended, endurance activities and can sustain activity for a long time without fatigue, making them suitable for endurance sports like marathon running.

Step 2: Identifying Marathon Runner Fiber Distribution

Professional marathon runners require good endurance, which suggests they would have a higher proportion of slow-twitch muscle fibers, helping them to sustain long distances without tiring quickly.

Step 3: Evaluating Answer Choices

Look at the answer choices: - (a) 80% fast-twitch, 20% slow-twitch is unlikely for endurance needs. - (b) 20% fast-twitch, 80% slow-twitch aligns with endurance athletes. - (c) 50% of each type doesn't strongly favor endurance. - (d) 40% fast-twitch, 60% slow-twitch presents a more balanced but less optimal distribution for a marathoner.

Step 4: Choosing the Most Likely Answer

The muscles of a professional marathon runner, who requires endurance, are most likely to consist primarily of slow-twitch muscle fibers. Therefore, option (b) 20% fast-twitch and 80% slow-twitch fibers is the most fitting choice.

Key Concepts

Fast-Twitch Fibers

Fast-twitch fibers, also known as Type II fibers, are specialized for quick and intense activities. These muscle fibers are capable of generating a lot of force in a short amount of time. However, this power is sustained only briefly as fast-twitch fibers tend to tire quickly.
They rely more on anaerobic metabolism to fuel their bursts of energy, which means they do not require oxygen in the same way slow-twitch fibers do.

• Ideal for sprinters and strength athletes.
• Rapid contractions and high force output.

These fibers are less efficient at using oxygen to create energy, which makes them less ideal for endurance activities. When it comes to activities like sprinting or weightlifting, fast-twitch fibers are activated to deliver explosive power.

Slow-Twitch Fibers

Slow-twitch fibers are the opposite of fast-twitch fibers in terms of function. Known for their endurance capabilities, these fibers can sustain activity for extended periods without fatiguing. They operate primarily through aerobic metabolism, meaning they efficiently use oxygen to produce energy.

• Best suited for endurance sports such as long-distance running.
• Increased mitochondrial density supports prolonged activity.

Slow-twitch fibers provide the stamina required for athletes engaging in marathon running or cycling. These fibers are less about producing big bursts of force and more focused on maintaining a steady production of energy.

Marathon Running

Marathon running is the epitome of endurance sports. A marathon is a long-distance running event with a standard length of 26.2 miles (42.195 kilometers). Success in marathon running depends heavily on stamina and the ability to efficiently use oxygen over a prolonged period.

• Requires high slow-twitch fiber percentage for sustained energy.
• Nutrition and training are key for energy conservation.

Runners often train extensively to optimize the proportion of slow-twitch fibers, enabling them to maintain a consistent pace and delay fatigue throughout the race. The longer a runner can maintain their pace, the better their performance is likely to be.

Endurance Sports

Endurance sports require an athlete to perform physical activity over extended periods. Unlike high-intensity sports, endurance sports demand sustained energy levels.

• Include activities like marathons, triathlons, and long-distance cycling.
• Training focuses on increasing aerobic capacity.

Athletes involved in these sports benefit from a higher proportion of slow-twitch muscle fibers, which enable their muscles to perform continuously without quick exhaustion. Endurance training enhances cardiovascular health and muscle efficiency, as well as increases slow-twitch muscle capacity.

Muscle Composition

Muscle composition refers to the ratio of different types of muscle fibers in a person's body. This composition can affect an individual's performance in various sports. Factors such as genetics and specific training can influence one's muscle composition.
Marathon runners typically have a higher percentage of slow-twitch fibers due to the demands of endurance running.

• Slow-twitch fibers favor endurance and efficient oxygen use.
• Fast-twitch fibers support quick bursts of power.

While genetic predisposition plays a significant role, dedicated training can slightly alter the muscle composition. Building a specific muscle composition through training helps athletes meet the physical demands of their chosen sport more effectively.