Final answer:
The recommended training zone intensity is 60-80% of the maximum heart rate reserve, which takes into consideration both the estimated maximum heart rate and resting heart rate.
Step-by-step explanation:
The training zone intensity recommended as a generalization should be within 60-80% of the maximum heart rate reserve. The maximum heart rate reserve is the difference between your maximum heart rate and your resting heart rate. To estimate your maximum heart rate, you can subtract your age from 220. For instance, a 40-year-old would have an estimated maximum heart rate of 180 beats per minute (bpm), while a 60-year-old's would be closer to 160 bpm.
When engaging in physical activity, maintaining a heart rate that falls within the 60-80% range of the maximum heart rate reserve helps ensure that the intensity of exercise is sufficient to improve cardiovascular fitness without overexertion.