As-it says in the Abstract you linked: "The 202.5–0.53∗age formula developed in the present study was the best in the studied population, yielding lowest mean e

As-it says in the Abstract you linked: "The 202.5–0.53∗age formula developed in the present study was the best in the studied population, yielding lowest mean errors in most groups, suggesting it could be used in more active individuals." Let's say it again — "suggesting it could be used". And "A simple formula predicting HRmax based on age only may be used when the exact HRmax is not needed or is difficult to obtain." For me the difference between 202.5 − 0.53·age and 211 − 0.64·age is less than 2 bpm!