Final answer:
Sarah should prioritize aerobic exercises like running, which target slow-twitch muscle fibers and improve the ability of her muscles to utilize oxygen efficiently, leading to enhanced cardiovascular endurance.
Step-by-step explanation:
To enhance her cardiovascular endurance, Sarah, a marathon runner, should focus on aerobic exercise. These exercises include activities like cycling, walking, and especially running, which Sarah is already practicing. Aerobic exercises are beneficial because they improve the efficiency of oxygen use by muscles during prolonged physical activity. As opposed to anaerobic exercise, which includes high-intensity bursts and is more suitable for developing muscle strength, aerobic activities are designed to improve endurance by engaging slow-twitch muscle fibers.
These slow-twitch fibers are important for marathon runners because they have more capillaries, mitochondria, and myoglobin, enabling them to carry more oxygen and sustain activity for a longer duration. Regular participation in aerobic exercise will gradually enhance Sarah's muscle endurance as well as her heart health, making it possible for her muscles to contract over long periods without tiring. While flexibility exercises like stretching are important for avoiding injuries, they do not directly increase cardiovascular endurance. Muscular endurance is closely linked to aerobic activities and is critical for marathon runners.
Therefore, while flexibility and muscular endurance are relevant to a marathon runner’s overall performance, the primary training approach for improving cardiovascular endurance is through consistent and progressive aerobic exercise.