A couple of days ago I received an email question from an athlete. He explained that his heart rate and power zones don’t agree and that there seems to be a two-zone separation with the power zones higher than the heart rate zones. I took this to mean that when he was in power zone 4 his heart rate was in zone 2. I get this question a lot, but it’s not always this relationship. Sometimes the athlete tells me that his or her heart rate zone is higher than the power zone.
I know of no research on anything like this. All I’ve got to go on is my experience in coaching athletes with power meters and heart rate monitors, including myself, for the past 10 to 12 years. I require all of the athletes I coach to have both devices and use them for every workout. I only coach four athletes a year, but they are a serious group and train a lot. So I’ve seen a lot of data over the years.
But before getting into what I’ve found regarding this athlete’s dilemma, let me explain the zones I use. The heart rate zones I use are found in tables in my books: The Cyclist’s Training Bible, The Triathlete’s Training Bible, The Mountain Biker’s Training Bible and Total Heart Rate Training. For power zones I follow Dr. Andy Coggan’s as described in his and Hunter Allen’s excellent book, Training and Racing With a Power Meter. His zones are based on functional threshold power (FTP) which is similar to lactate threshold or anaerobic threshold. It’s the power you can sustain for an hour in a race. Coggan’s zones are as follows.
PZ1 <55% of FTP
PZ2 56-75% of FTP
PZ3 76-90% of FTP
PZ4 91-105% of FTP
PZ5 106-120% of FTP
PZ6 121-150% of FTP
PZ7 >150% of FTP
If you’re not using these two sets of zones for heart rate and power then what I’m about to explain may well not apply to you at all. Please bear that in mind if you have a question to post here. I am not familiar with other zone systems so can’t comment on why yours don’t agree in that case. In fact, you’d be amazed at what I don’t know about other coaches and their methodologies. I have a hard enough time just keeping up with stuff that is critical to my growth as a coach. There simply isn’t enough time to know what others are doing and why. I’m pointing this out upfront because I get lots of questions assuming I know things. Best not to do that if you have a question.
So now let’s get back to the issue at hand: Why don’t the heart rate and power zones always agree?
I should start by saying I have never had an athlete whose power and heart rate zones were exactly the same all the time. But for most the zones have overlapped by quite a bit. So, for example, when one of these athletes with overlapping zones is in high zone 2 heart rate, he or she may be in low zone 3 power. That’s quite common.
Having only a small overlap is not unusual either. There may only be a narrow range in which the zones overlap. Having a complete one-zone gap is also not unusual. A two-zone gap, as the questioner said he experienced, is unusual but not unheard of.
Testing is a key variable here. As mentioned, it’s necessary to know your FTP in order to set up power zones. The same goes for finding lactate threshold heart rate (LTHR) in order to set up your heart rate zones. If the tests to establish FTP and LTHR are remiss then the zones will not be accurate and unusual gaps are likely. So the first issue is that self-testing must be accurate. The more times you do the FTP and LTHR tests the more accurate the zones will become.
His issue was that his heart rate zones were low relative to his power zones. That’s actually a good problem to have at this time of year. The most likely reason for this is that aerobic fitness is very high and exceeds muscular fitness. So the heart does not have to beat as fast to provide oxygen to the muscles. This implies the need to improve one’s power.
Having a high heart rate when power is low is a less attractive problem to have and is more likely to occur when aerobic fitness is sub-par. This also may be the situation after an illness or when highly fatigued. It may even be an indicator of overreaching and is likely to show up after a lengthy block of crash training. If so, rest is the most likely solution. But it could also be that more aerobic training is needed.
The bottom line here is that it’s not unusual to have some discrepancy between heart rate and power zones. It may even be fairly common with both sets of zones fluctuating due to the constantly changing interplay of fitness and fatigue. However, heart rate is likely to change the least, I believe. Power is much more sensitive to training.
I wish I could give you hard data to back up my beliefs here, but there are none. I continue to monitor such situations (I currently have one going with an athlete I coach which is probably related to extended overreaching). If I learn more on this topic I’ll certainly post it.