Mhr should be calculated
a. during an intense exercise routine
b. prior to an initial exercise routine
c. immediately following the exercise routine
d. 20 minutes after an exercise routine
i'd really appreciate your ! ! ^^

Maximum heart rate should be calculated immediately after an exercise routine. Maximum heart rates vary with age and the exercise activity performed. It refers to the maximum capacity of the heart to supply blood throughout its entire system. Maximum heart rates are also based on exercise intensity/target zones to keep track how an individual is performing or should perform in an exercise activity. It is estimated to be calculated as 220 minus your age. Why 220? Because it is the only maximum number of beats per minute that the human heart could actually perform in a lifetime. 

The answer is organisational websites.