A colleague told me that recent research has shown that max heart rate is not age related, it's genetically determined. Thus a higher max does not necessarily mean that one is in better shape, nor does max heart rate increase when getting in better shape (also as a result of it being genetically determined). Is this true? What is this research? And is it then only possible to estimate a max heart rate by doing a submax or max test?
You are correct in stating that maximum heart rate does not increase with fitness (furthermore, it never was presumed to; this confusion may come from the ability to withstand greater physiological and metabolic discomfort with an increase in fitness and therefore actually reach true maximal heart rates as opposed to being limited by other factors). Yes, at this stage of research, maximal heart rate is identified as being genetically determined and is influenced by age but not gender.
So how does an increase in fitness affect heart rate?
Cardiac Output = Heart Rate x Stroke Volume
There are two key fitness adaptations that bring about an increase in stroke volume. The first is an increased Left Ventricle End Diastolic Volume (LVEDV) or Preload (more simply, the ventricle fills with more blood), and the second is the increase in pumping force through an increase in size of the cardiac muscle of the left ventricle and the increased presetretch caused by the increased LVEDV.
With this increase in Stroke Volume (even though maximal heart rate remains the same), there is an increase in the Cardiac Output. Likewise, if you require X amount of blood per minute (Cardiac Output) to keep the body functioning at rest/sub maximal exercise, the increase in Stroke Volume means the heart does not need to pump as often, hence a decrease in resting/sub maximal heart rate for the given intensity (a measure of fitness).
Now consider the concept of heart rate reserve (HRR). The "room to manoeuvre" for the heart rate is between maximal heart rate (highest) and resting heart rate (lowest); this difference is called the HRR. With fitness decreasing the resting heart rate, there is an increase in HRR and therefore response ability of the heart.
As for determining your maximal heart rate, the only way to do it correctly is to perform a Maximal Heart Rate test (aside from the health concerns if unfit, fatigability may limit your ability to reach a true maximal heart rate). As for predicting maximal heart rates at this stage, the 220 minus your age is claimed to underestimate values for older adults. With this in mind, the latest formula - which corrects this deficiency -is 208 minus 0.7 (age).
This formula is said to have greater predictive value for maximal heart rate than the previous formula; however, the developers do remind us that the result may be inaccurate by as much as 10 beats per minute (the standard deviation of the study).
As an adjunct, many of the sub maximal tests still employ the 220 minus your age formula and hence carry the associated deficiencies.