The answer is the last one (e): All of the above may limit VO2 max.
Explanation for each option:
a. Maximal heart rate: This is the highest number of beats per minute your heart can achieve during maximum physical exertion. It is a key factor in determining cardiac output (the amount of blood the heart pumps per minute), which directly influences VO2 max.
b. Maximal stroke volume: This is the amount of blood ejected by the left ventricle of the heart in one contraction. Higher stroke volume means more blood (and thus more oxygen) is delivered to the muscles, which can enhance VO2 max.
c. Arterial oxygen content: This refers to the amount of oxygen carried by the blood. Higher arterial oxygen content means more oxygen is available to be delivered to the muscles, which can improve VO2 max.
d. Oxygen extraction by skeletal muscle: This is the ability of muscles to extract and use the oxygen delivered by the blood. Efficient oxygen extraction is crucial for high VO2 max, as it determines how well the muscles can utilize the available oxygen.
e. All of the above may limit VO2 max: Since each of the factors listed (maximal heart rate, maximal stroke volume, arterial oxygen content, and oxygen extraction by skeletal muscle) plays a critical role in determining VO2 max, any one of them can be a limiting factor. Therefore, the correct answer is that all of the above may limit VO2 max.
Summary:
All the factors listed (maximal heart rate, maximal stroke volume, arterial oxygen content, and oxygen extraction by skeletal muscle) can limit VO2 max, making option (e) the correct answer.
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