Final answer:
Muscular endurance is the component of fitness that enables sustained exercise, largely determined by the ratio of slow-twitch to fast-twitch muscle fibers.
Step-by-step explanation:
The component of fitness that allows individuals to sustain exercise for a longer period of time is muscular endurance. This aspect of fitness is significantly influenced by the proportion of slow-twitch to fast-twitch muscle fibers in an individual's muscles. Those with a higher amount of slow-twitch fibers generally develop greater endurance, benefiting from their fibers' capacity to carry more oxygen and efficiently support aerobic activities, such as running or cycling, for extended periods.
A factor contributing to these different results includes genetic differences affecting muscle composition. Aerobic exercise, like walking or jogging, uses a relatively high percentage of slow-twitch muscle fibers, which consume vast amounts of oxygen, allowing for improved cardiovascular endurance and sustained physical activity.