Compare Type I and Type II fibers in terms of contraction speed, force output, and typical training adaptations, and indicate which fiber type is favored by strength and power training.

Compare Type I and Type II fibers in terms of contraction speed, force output, and typical training adaptations, and indicate which fiber type is favored by strength and power training.

• A. Type I fibers are fast-twitch, generate high force; Type II fibers are slow-twitch and fatigue resistant; strength/power training favors Type II.
• B. Type I fibers are slow-twitch, generate lower force but are highly fatigue resistant; Type II fibers are fast-twitch, generate higher force, fatigue more quickly.
• C. Type I fibers are slow-twitch, generate lower force but are highly fatigue resistant; Type II fibers are fast-twitch, generate higher force, fatigue more quickly; strength/power training preferentially recruits and hypertrophies Type II fibers.
• D. Type I fibers have greater cross-sectional area than Type II and produce more force; strength training favors Type I.

Answer: (C)

The key idea here is how fiber types differ in function and how training shapes them. Slow-twitch (Type I) fibers contract more slowly, produce less force per contraction, but are highly fatigue resistant, which makes them well suited for prolonged, endurance activities. Fast-twitch (Type II) fibers contract rapidly and generate much higher force, enabling powerful, explosive movements, but they tire more quickly. When it comes to training adaptations, strength and power work relies on recruiting and enlarging the fast-twitch fibers. Heavy, high-intensity training increases the size and neural efficiency of Type II fibers, boosting maximal force and power output. Endurance-focused training, by contrast, tends to emphasize the characteristics of Type I fibers, enhancing their oxidative capacity and fatigue resistance. Within Type II, there are subtypes in terms of fatigue and speed (IIa being more fatigue resistant and oxidative, IIx more explosive but fatigue-prone). The overall takeaway is that strength/power training preferentially targets and enhances Type II fibers.

The key idea here is how fiber types differ in function and how training shapes them. Slow-twitch (Type I) fibers contract more slowly, produce less force per contraction, but are highly fatigue resistant, which makes them well suited for prolonged, endurance activities. Fast-twitch (Type II) fibers contract rapidly and generate much higher force, enabling powerful, explosive movements, but they tire more quickly.

When it comes to training adaptations, strength and power work relies on recruiting and enlarging the fast-twitch fibers. Heavy, high-intensity training increases the size and neural efficiency of Type II fibers, boosting maximal force and power output. Endurance-focused training, by contrast, tends to emphasize the characteristics of Type I fibers, enhancing their oxidative capacity and fatigue resistance.

Within Type II, there are subtypes in terms of fatigue and speed (IIa being more fatigue resistant and oxidative, IIx more explosive but fatigue-prone). The overall takeaway is that strength/power training preferentially targets and enhances Type II fibers.