A client's maximum heart rate must be established prior to administering the YMCA 3-minute step test. This is achieved by:
a. subtracting the client's age from 220.
b. subtracting the client's resting heart rate from 220.
c. subtracting the client's age from 220, then subtracting the client's resting heart rate.
d. subtracting the client's age from 220, then multiplying by 60-90%.