Final answer:
Several factors can limit the amount of oxygen used by muscles, including the availability of oxygen in the atmosphere, transport system efficiency, muscle's oxygen extraction capability, and an individual's fitness level.
Step-by-step explanation:
The maximal capacity of the systems supplying oxygen to muscles can be limited by several factors. The availability of oxygen in the atmosphere can limit the amount of oxygen, as this is the source of all oxygen for aerobic organisms. The efficiency of the oxygen transport system, which includes how well the lungs, blood, and cardiovascular system work together to transport oxygen to the muscles, greatly influences oxygen use. Moreover, the muscle's ability to extract oxygen from the blood plays a vital role; myoglobin within the muscles can store oxygen, and higher levels of myoglobin improve oxygen extraction. Finally, the individual's fitness level impacts how effectively oxygen is used, as aerobic training enhances both the circulatory system and the capacity of muscles to utilize oxygen effectively.