If something is written down often enough, people will begin to believe it is true.
We see so often the generic Max Heart Rate calculation formula 220 - age. I hear so many people say things like:
"I'm 40 and my HR got up to 180, but I felt fine. Should I go see a doctor?"
"I'm trying to exercise in my target HR but I feel like I'm killing myself."
I'm hoping to raise people's awareness of just how flawed 220 - age is. It is not useless. It is easy to remember, easy to calculate, and may make a reasonable estimate for much of the population.
However, it has a standard error of about 10 bpm (depending on your source). Standard error means that ~67% of the population will fall within 10 beats of the formula. 95% of the population will have a range of 40 beats per minute (20 to either side). Another way to think about it is that 1/3 of your clients will fall 10 or more beats per minutes away from the 220 - age formula. 1 in 20 may be 20 beats away from the formula.
For example, say you have a 40 year old client with resting HR of 70:
220 - 40 = 180 theoretical maxHR.
Based on that, say you suggest a targetHR of 80% HRR = 158.
If your client's actual maxHR is just one standard deviation lower (170), then you've inadvertantly suggested a target of 88% of maxHRR.
The ACE Personal Trainer Manual just barely mentions this. If you want to read a lot more about it, someone recently pointed out the following excellent article:
Highly recommended reading if you use target heart rates.
quote:...takes into consideration the person's resting heart rate.
To clarify, most target heart range recommendations rely either on % of MaxHR, or % of Heart Rate Reserve (which incorporates resting heart rate and MaxHR). Either one relies on a reasonably accurate assessment of MaxHR.
Heart Rate Reserve & lactate threshold
Frisbee wrote: I take 220-age-RHR x 65% + RHR = THR
That's the basic Karvonen (heart rate reserve) method with an estimated MaxHR. That is the same formula I used in my calcuation above, but I didn't write out all the steps of the math. I'll restate the example using 65% and show more math:
Example: say you have a 40 year old client with resting HR of 70:
220 - 40 = 180 theoretical maxHR.
Carrying out your formula for a 65% target:
(180 - 70)*.65 + 70 = 72 + 70 = 142 suggested target heart rate.
Now, let's say your client's actual max heart rate is one standard deviation lower (170). That would mean the calculations should have looked like this:
(170 - 70)*.65 + 70 = 72 + 70 = 135 ACTUAL 65% of HRR.
The recommendation of 142 would really be recommendation for 72% of HRR.
It is unlikely that your client's perceived exertion would match your expectations. She is working a lot harder than you would expect.
Resting heart rate provides a correction, but it is not enough to counter the fallibility of 220 - age.
Frisbee wrote: what about lactic acid threshold testing?
If you mean in a lab with blood draws, it provides excellent information about pace. However, lactate threshold is, fortunately, quickly trained. Because it is changing, your client should in theory have this checked regularly. I don't imagine I will ever have clients willing to subject themselves to regular laboratory lactate threshold testing, let alone afford it. (The same test would, however, probably get me a good working MaxHR.)
If you mean using normal models to estimate lactate threshold, I find them difficult to apply. The only common non-lab, yet well accepted test I'm aware of is the "point of deflection" method. In my limited experience, it is hard to zero in on that point of deflection. It is an interesting test to give to a client who is interested and ready to train hard. But I make sure they are aware that it is a fallible test. Furthermore, I wouldn't give it to someone who was not in very good condition.
The VO2Max tests in the ACE trainer manual (and similar tests from other sources), I've found to be quite fallible. I do use some of them because they aren't terrible. Also, there are enough to choose from that you can give one which is appropriate to the client. (E.g., few clients would be unable to handle the Rockport 1 mile walk test.)
But the bottom line is that you must tune into your clients' percieved exertion so that you can recognize when your tests and formulas are off.