Final answer:
The target heart rate for a 40-year-old man with a resting heart rate of 70 bpm exercising at an intensity of 65% using the HRR method is approximately 142 bpm.
Step-by-step explanation:
The target heart rate (THR) during exercise can be calculated using the HRR (Heart Rate Reserve) method. The HRR is calculated by subtracting the resting heart rate (RHR) from the maximum heart rate (MHR). The MHR for a 40-year-old man can be estimated using the formula 220 - age, which gives us a maximum heart rate of 180 bpm. The target heart rate is then determined as a percentage of the HRR.
To find the target heart rate at an intensity of 65%, we first need to calculate the HRR by subtracting the resting heart rate from the maximum heart rate:
HRR = MHR - RHR
HRR = 180 bpm - 70 bpm
HRR = 110 bpm
Next, we calculate the target heart rate by multiplying the HRR by the intensity percentage and adding it to the resting heart rate:
Target HR = (intensity * HRR) + RHR
Target HR = (0.65 * 110 bpm) + 70 bpm
Target HR = 71.5 bpm + 70 bpm
Target HR ≈ 142 bpm
Therefore, the target heart rate for a 40-year-old man with a resting heart rate of 70 bpm exercising at an intensity of 65% is approximately 142 bpm.