Final answer:
Stuart and his brother experience moderately intense heart rates while jogging and engaging in a conversation. The intensity of their activity is likely vigorous as they can only speak a few words between breaths. Monitoring conversation ability during exercise can help determine activity intensity.
Explanation:
Moderate: While jogging with the ability to speak a few words between deep breaths, Stuart and his brother experience moderately intense heart rates.
Vigorous: If their conversation is limited to one or two words due to heavy breathing, their heart rates suggest a vigorously intense activity.
Cardio exercise intensity can be subjective, measured by the talk test where moderate activity allows conversation but not singing, while vigorous activity only permits a few words before pausing for a breath.
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