Adults who are beginning a new exercise regimen are often advised to perform this test only in the presence of medical staff due to risks associated with high heart rates. For general purposes, a formula is often employed to estimate a person's maximum heart rate. However, these predictive formulas have been criticized as inaccurate because they generalized population-averages and usually focus on a person's age and do not even take normal resting pulse rate into consideration. It is well-established that there is a "poor relationship between maximal heart rate and age" and large standard deviations relative to predicted heart rates. ("see Limitations of Estimation Formulas").