Forgive me if I'm off some here as I'm diving way back in my memory bank, but this is what I remember from my exercise physiology classes.
The two main times you want to be careful with this are,
- When the person is highly trained
- When the person is older
Lance Armstrong was heavily studied in his heyday:
(Note, this was a highly debated paper due to the efficiency gained finding, but I don't see any issue using the max heart rate numbers.)
- At 21 years old, Lance's max heart rate was 207
- At 28 years old, Lance's max heart rate was 200
You can see he's over performing what 220 - your age would give. From an absolute standpoint, it's not a huge over performance, but from an athletic standpoint it is.
When does a person become "trained"? I don't remember ever getting a clear answer on that. But it is not just because you jog here and there.
Nor is it so consistent where once a person is trained, you know they'll over perform by X amount. There is enough variability you have to approach each person as their own, otherwise, if you're say, programming someone's endurance work, you could be off by a considerable amount.
What I remember when in the lab was, if a person has some serious endurance training background, just beware they might not fit the models as well. In fact, I think they often underperform. (They get really good at producing more blood per beat, opposed to beating faster.)
Next, being older,
1) A regression equation to predict HRmaxis 208 − 0.7 × age in healthy
2) HRmaxis predicted, to a large extent, by age alone and is
independent of gender and habitual physical activity status. Our
findings suggest that the currently used equation underestimates
HRmaxin older adults. This would have the effect of underestimating
the true level of physical stress imposed during exercise testing and
the appropriate intensity of prescribed exercise programs.
The gist being as age goes up, the traditional formula progressively holds up worse compared to the regression equation they found,
Back to physical activity:
As you can see, this study didn't find a difference based on activity level, but their criteria wasn't e.g. high level athlete. It was simply that the person engage in endurance training a few days per week for at least a couple years. That ain't Lance Armstrong.
Second, they did find a difference, but it wasn't statistically significant. As I hit on before, the differences tend to be small, but noticeable when you're focused on high level performance.
For instance, in their lab based study,
Again, no significant differences in the HRmaxregression equation were observed between men and women or between sedentary (212 − 0.7 × age) and endurance-trained (205 − 0.6 × age) subjects.
But, for a 25 year old,
- 212 - 0.7 × 25 = 195
- 205 − 0.6 × 25 = 190
In research, "no difference" often doesn't mean zero difference. Statistical relevance != clinical.
(And just to show the inconsistency, here's master's athletes over performing the traditional formula.
Their average age was 59, but average max heart rate was 169. It's possible everyday runners on average underperform (stronger heart), but then really high level people over perform (stronger and faster).)
Furthermore, through the adult lifespan, the standard deviation in beats was still 7 to 11. That's a pretty big chunk we could possibly just chalk up to genetics.
The authors even show how in their model, you could still be off by 20 beats due to the standard deviation. Modeling humans is hard :).
Sorry if that's all a bit convoluted, but that's kind of the point. As they write, if it's important, you should directly measure for that person.
Essentially, you always have to worry about using the formula, but you worry more when the person is highly endurance trained and or older.
A much easier way to go about programming is to take the person's best time and use percentages off that.
Lastly, and where you have to be really careful with the older crowd, is medication can throw this all out of wack. When a person is on blood pressure medication, you don't want to be looking at heart rate at all. The medication purposely limits how high the blood pressure can go, which is going to affect how much output the heart can generate. You can have people feeling exhausted at only 90 beats per minute. (Little longer discussion.)
In which case you really need to be going based on how the person feels. I've seen trainers damn near make someone collapse because they thought the person was lying to them about how hard they were working, since the trainer was so focused on the low heart rate.