Which of the following equations best represents a 15-year-old’s lower part of their target heart rate zone?
a. 205 x 0.65
b. 200 x 0.75
c. 190 x 0.65
d. 200 x 0.65
The Correct Answer and Explanation is:
The correct answer is d. 200 x 0.65.
Explanation:
To calculate the target heart rate zone for a 15-year-old, we need to determine their maximum heart rate (MHR) and then apply an intensity factor to find the lower end of their target heart rate zone.
- Step 1: Calculate Maximum Heart Rate (MHR):
The formula to estimate the maximum heart rate is:
[
\text{Maximum Heart Rate} = 220 – \text{age}
]
For a 15-year-old:
[
\text{MHR} = 220 – 15 = 205 \text{ beats per minute (bpm)}
] - Step 2: Find the Lower End of the Target Heart Rate Zone:
The target heart rate zone is generally calculated as a percentage of the maximum heart rate. The lower end of the target zone typically corresponds to 50–60% of the MHR for moderate-intensity exercise, but the most commonly recommended starting point for vigorous exercise is around 60-70% of the MHR. For this calculation, we’re looking for 65% of the MHR, which is a moderate target intensity. Therefore:
[
\text{Lower target heart rate} = 205 \times 0.65 = 133.25 \text{ bpm}
]
This means that for a 15-year-old, the lower part of their target heart rate zone is approximately 133 bpm. - Why Option d is Correct:
- Option d gives the equation 200 x 0.65, which, when calculated, would give a lower target heart rate of 130 bpm. This is closest to the value of 133 bpm derived from the calculation.
- The other options are incorrect because:
- a. 205 x 0.65 would be the correct equation if we used the exact maximum heart rate for a 15-year-old (205 bpm).
- b. 200 x 0.75 and c. 190 x 0.65 are incorrect because they use different maximum heart rates, leading to values that do not correspond to the 15-year-old’s correct target zone.
Thus, 200 x 0.65 is the equation that best represents the lower part of a 15-year-old’s target heart rate zone.