After reading through Training for the Uphill Athlete I picked up a heart rate monitor (a Fitbit Inspire HR) and have started using the treadmill three times a week for an hour at a time. I wanted to record my starting stats so that I could refer to them later in the year.
In order to build endurance 80-85% of your exercise volume needs to be in heart rate zones 1 and 2. The book suggested using Phil Maffetone’s 180 formula to determine the beats-per-minute that define the upper limit of your zone 2. The formula is simple:
Zone 2 bpm = 180 – age
There’s an additional adjustment of adding or subtracting 5 bpm depending on whether you’re in particularly good shape (add 5) or just starting out (subtract 5).
Since I’m 40 and just starting out (as far as serious training is concerned) I calculated a zone 2 limit of 135 beats per minute.
On a treadmill this corresponds to walking at 3.8mph at an incline of 2%. Anything even slightly resembling a jog, going all the way down to 3.3mph and no incline, results in a heart rate of at least 140bpm. I don’t know how much margin of error is acceptable but walking quickly at a slight incline seems far too easy to be doing any good. Something seems off.
One thing I’ve noticed is that my resting heart rate is appallingly low. It’s 60 as I’m typing this but the Fitbit says that it’s typically in the low 50s when I’m wide awake. Over the years I recall more than one doctor telling me that I had the heart rate of an Olympic athlete but I’ll be the first to admit that I am not in what most would consider amazing shape. My best mile time is just under eight minutes and my sustainable pace for a 10k is a lousy 12 minutes per mile. On the other hand I can’t remember the last time I actually got winded while backpacking (Aasgard Pass doesn’t count). And although a resting heart rate of under 60 beats per minute meets the technical definition of bradycardia (too-low heart rate) I’m assuming that since multiple doctors have pointed out my low heart rate but never suggested that anything needed to be done about it that it’s not really an issue. Still, I wonder if this has some effect on what my zone 2 limit should be as far as the formula is concerned.
The other method of determining your target heart rate is to calculate your lactate threshold. Lactate is a byproduct of exercise and the amount generated corresponds with the intensity of the activity (heart rate, more or less). At some point you will produce more lactate than your body can process which will cause it to build up until you become exhausted. The amount of lactate that you can process is your lactate threshold and any intensity of exercise below this threshold should be sustainable almost indefinitely as far as muscle fatigue is concerned. In fact, the whole idea behind training for endurance is to increase this threshold.
Unfortunately determining this value requires measuring the amount of lactate in your blood which means spending hundreds of dollars either on a portable lactate meter or on a lab test. Fortunately Metier, which appears to be a high-end cycling shop here in Seattle, offers a lactate test for under $200. Sign. Me. Up.