I decided to post this here since I posted it on other sites. Maybe if someone knows more about this than I do, they’ll make a comment about it. 
http://www.ultrafitness.net/article_3.htm
Near the bottom of this web page, you’ll see how to calculate your five training levels using the Karvonen method. Let’s use an example to illustrate the lower and upper limit of level one.
Measured maximum heart rate (MMHR): 191
Measured resting heart rate (MRHR): 58
Heart rate reserve (HRR): MMHR - MRHR = HRR: 191 - 58 = 133
Level one
lower limit = HRR x .60 + MRHR = 133 x .60 + 58 = 79.8 + 58 = 137.8
upper limit = HRR x .70 + MRHR = 133 x .70 + 58 = 93.1 + 58 = 151.1
These are the results using the Karvonen method but using the results of the VO2Max to calculate the lower and upper limit of level one, you’ll get:
Level one: the heart rate at 55%-65% of your VO2Max
Here, you check the heart rate at 55% of the VO2Max for the lower limit. Since my VO2Max was 56, then 55% would be 30.8 ml/kg/min At 30.4 ml/kg/min (the closest I can find on the results of the test), my heart rate was 143 beats per minute. 65% of my VO2Max would be 36.4 ml/kg/min and at 37.3 ml/kg/min (the closest I can find on the results of the test), my heart rate was 159.
Although the Karvonen method came up with 137.8 and 151.1 beats per minute, the method using the results of the VO2Max came up with 143 and 159 beats per minute. So, I ended up averaging both and rounding the numbers so I came up with 140 to 155 beats per minute for my level one. (You can see 37.3 is higher than 36.4 so I know I can safely assume the upper limit would be closer to 155 instead of 159 bpm.)
I have to note here that at the same speed on a treadmill, I can fluctuate between 138 to 143 beats per minute. That’s at least five beats per minute difference at the same speed. So, results of the VO2Max may not come out completely in line with what you’d expect. And the results I got were taken at 30 second intervals which may not come out with the EXACT numbers you were looking for (like exactly 55% or 65% of your VO2Max).
Both methods of calculating your five training levels are described in the book Serious Training for Endurance Athletes by Rob Sleamaker and Ray Browning (the Karvonen method and VO2Max results).
Let’s exaggerate some figures to see what kind of difference we can see for the lower limit of level one using the Karvonen method.
Let’s imagine a max of 210 beats per minute and a low of 40.
(HRR = 210 - 40 = 170)
lower limit = HRR x .60 + MRHR = 170 x .60 + 40 = 102 + 40 = 142
Or, let’s take an a max of 185 and a low of 65.
(HRR = 185 - 65 = 120)
lower limit = HRR x .60 + MRHR = 120 x .60 + 65 = 72 + 65 = 137
There’s something odd about this method since it shows people with VERY different highs and lows could have about the same lower limit for level one. And some people say they have to WALK to get under 150 beats per minute while others say it’s easy for them to go over 170 bpm on an easy effort. So, I’d encourage everyone to still get a VO2Max (treadmill test) to determine your five training levels. (You can ask for a copy of the results then use those results to calculate your training levels.)
Again, using the results of the VO2Max, you would use the heart rate you were at when you were at 55% and 65% of your VO2Max to calculate the lower and upper limit of level one.
Level two would be 66-75%
Level three 76-80%
Level four 81-90%
Level five 91-100%