The first is the + 10 on the age predicted formula (Astrand and Rodahl 1977).
Second is using the more generalized method (maximum heart-rate – MHR) of calculating THR without figuring out a resting heart rate (RHR – Karvonen formula).
And even when factoring RHR, there are medications and other factors that may affect the accuracy of this calculation – beta-blockers for hypertension or migraines, and heart disease.
And finally, there is the possibility of errors when performing the pulse check; the length of the count, the error margin with the count starting point, a multiplication error, or a miscount due to the beat of the music.
For all of these reasons, it has long been the standard to include other methods of measuring intensity, such as perceived exertion and the “talk test”, along with pulse checks.
Essentially, these are subjective means of measuring intensity – if you feel like you are working hard, you probably are. If in an attempt to talk, it is somewhat breathless or stilted, your cardio-respiratory system is working hard in an attempt to send oxygen to your exercising muscles. But these means alone require you to have an idea of how hard is hard, and how breathless you should be according to your fitness goal.
Heart rate monitors, however, can help anyone starting out get a better idea of where they need to be working, how hard they should be breathing, and also give a more definite way of measuring fitness gains over time. Because they also use the maximum heart-rate formula, there is some room for error, but it is relatively minimal, and the readings will at least be consistent.
While they do require some set-up, heart rate monitors are available in a wide assortment with various options and pricing, are fairly easy to use, and provide instantaneous feedback without having to stop to count or calculate.
In the group fitness setting and even in video workouts, fewer instructors are using target heart rate checks, most do energy exertion checks or perceived exertion, but some in group fitness simply ask “how ya’ doin?”.
If you are new to exercise, in an exercise rut or have reached a fitness plateau, or if you are serious about improving your overall fitness, a heart rate monitor may be worth the investment. But if you are not gadget inclined, you should at least have an understanding of the perceived exertion and talk test methods of measuring exercise intensity.