ACE Personal Trainer Practice Exam 2025 - Free Personal Trainer Practice Questions and Study Guide

Type 1 muscle fibers, also known as slow-twitch fibers, are characterized primarily by their ability to use aerobic metabolism for energy production. This means they rely heavily on aerobic glycolysis and fatty acid oxidation, enabling them to sustain prolonged activities that require endurance, such as long-distance running or cycling.

These fibers contain a high density of mitochondria and myoglobin, which contributes to their efficiency in utilizing oxygen and producing energy over extended periods. Their primary function is to support activities that require endurance and stamina rather than quick bursts of power or speed, which is why they are not typically suited for high-intensity or short-duration activities.

In contrast, other descriptions, such as high glycolytic capacity and fast twitch, do not align with the characteristics of Type 1 muscle fibers. These fibers are not meant for activities that rely on anaerobic energy systems, which would involve high glycolytic capacity or fast-twitch attributes. Therefore, the statement regarding aerobic glycolysis and fatty acid oxidation accurately describes the fundamental nature of Type 1 muscle fibers.