Final answer:
Oxidation occurs during low-intensity aerobic exercise, mainly using fatty acids as fuel and targeting slow-twitch muscle fibers. Marathon runners, who often have a higher proportion of slow-twitch fibers, provide a good example of athletes relying on aerobic metabolism.
Step-by-step explanation:
Oxidation primarily occurs during low-intensity aerobic exercises. Aerobic metabolism is favored in these conditions because it produces larger amounts of ATP, which is necessary for sustained muscle contraction over a longer period. In a low-intensity setting, the body mainly uses fatty acids as the fuel source, with a small amount of glucose also being utilized. Slow-twitch muscle fibers, which are dense with capillaries and rich in mitochondria, are the primary targets during these activities. While fatty acid reserves are nearly unlimited, allowing for extensive activity duration, glycogen stores can be depleted, leading to fatigue.
Athletes who perform endurance sports, such as marathon runners, usually have a higher proportion of slow-twitch fibers which are well-suited for aerobic exercise. This exercise type enhances cardiovascular endurance and can also contribute to muscle toning. It includes activities such as cycling, swimming, and brisk walking. It is important to note that there is considerable variation in individual responses to exercise, influenced by genetic differences in muscle fiber composition.
From the options provided, option 'a' is the most accurate. Oxidation kicks in during low-intensity aerobic exercise, targeting slow-twitch muscle fibers and utilizing fatty acids, with marathon runners being a prime example of athletes who utilize this energy system.