Which description best fits Slow Twitch Type I motor units?

• A. Fastest contraction times and largest forces
• B. High glycogen content with rapid fatigue
• C. Slow nerve transmission, small forces, fatigue-resistant
• D. Moderate contraction speed with moderate force

Answer: (C)

Slow twitch Type I motor units are built for endurance: they contract slowly, generate smaller forces, and resist fatigue because they rely on aerobic metabolism with high oxidative capacity, supported by many capillaries and abundant myoglobin. This combination means they produce light, sustained contractions and can keep working longer without tiring. The description that best fits them is the one highlighting slow nerve transmission, small forces, and fatigue resistance.

Other options describe fast-twitch or intermediate properties: very fast contraction times with large forces belong to fast-twitch fibers that generate high power but fatiguе quickly; high glycogen content with rapid fatigue points to fast glycolytic fibers; moderate contraction speed with moderate force fits intermediate fibers, not the slow-twitch type.