I have no desire for this to become a thread on HRMs. There's a lot more I want to discuss. But let me write to counter some stuff I’ve read over the years against HRMs. These can be everything from “Kenyans don’t wear HRMs” to “I have a high-low-whatever HRmax and the training zones don’t work with me...”
In the nicest possible way, whenever I hear someone say, "I'm definitely an exception", I think to myself, well that's probably unlikely... What is more likely is that what we have here is a lack of complete understanding of what's going on.
It's like people who claim, "heart rate monitors don't work for me..." What we really have there is someone who does not like, or understand, the info that the HRM is telling him / her. Usually it is the case that when they are running at what they think is their "correct" training pace (perhaps gleamed from Jack Daniels' Vdot tables based on their recent 5k race pace) they suddenly find the HR is wayyy too high for that pace. So they just (choose to) believe they must be some kind of genetic outlier (because the Vdot tables are always right, everyone sez so), and the HRM goes in the drawer for good.
I guess I could pick up a pencil and manage a coupla stick figures like matchstick men. But with the same pencil in the hands of Leonardo we get the study sketches he used for the Last Supper. So, what's REALLY at fault here when I cannot get the self-same pencil to do what Leonardo can get it to do: is it me or is it the pencil?
An HRM, just like a pencil, is a tool. And a tool is only as good as the person using it. I don’t know why they sell these things without telling you everything you can learn from them. They give you HR training zones based on age-percentages (which are not accurate) and tell you very little else. Let me try and pass on at least some of what an HRM can tell me...
I often liken an HRM to a Rev Counter in a car. Of course every car has a speedometer so we can tell how fast the vehicle is traveling, but few cars (perhaps only the more sporty) will have a rev counter which informs the driver how hard the engine is having to work (to manage the speed of travel). Note that race drivers (Formula I) most definitely have a Rev Counter in their car: im other words, knowing the speed does not tell them all they need to know.
I have a rev counter on the bike: when I am in top gear I might be travelling at 100 km/hr at 6,000 rpm. If I change DOWN a gear, the rpm goes UP... despite the fact I am still doing 100 km/hr. So pace (alone) does not tell you how hard your "engine" is working.
I can imagine observing two runners side by side doing a run, or workout, together. The fact that they are side by side lets me know how fast they are running, but it does NOT tell me how hard each of them is working to achieve that pace.
If I am far enough away, then I might be excused for not realizing that one is working just-a-little-bit harder than the other during the workout. Of course, with years of experience, I can easily pick up any number of other clues; breathing rate, degree of “comfort” or smoothness of movement; who is recruiting more muscle mass to deal with the pace (eg: stride length)... but if the two are close enough in ability, it can be difficult to tell precisely who is working harder than whom.
An HRM on each of them would tell me straight away, especially up to HM pace (or a shade faster) as I discuss above... the rising HR on one of them would warn me that he/she is working harder than I want them to. Even if they were doing one of Cabral’s intermittent sessions, an HRM would be able to show me (inter alia) speed of recovery (how quickly HR falls post-interval), or how high HR climbs on each successive interval.
Therefore although the workout might be governed by a set pace, I can still monitor HR above LT to make sure the training provoked the right effort. If the runner is wearing an HRM, I can check that the pace I gave them is not too hard that night (perhaps due to tiredness brought over from previous sessions).
I mentioned above that I might curtail a session if I thought the runner was working harder than I wanted. Some readers might take that to mean that I am waiting to learn if the HR is higher than I would expect at that running pace.
Actually the opposite is much more likely to be true; I stop the session because the HR is much lower than I expect it to be for the pace involved.
This seems paradoxical. And it often appears that way to runners until I explain to them precisely what the HRM is telling them.
Let’s say I expect an HR for this session in the range of 180-185. I expect it because I know the pace involved, I know what percent HRmax such a pace should require, and I may even have done the same session with this runner in the past, so I know precisely what to expect. I’m not expecting any surprises.
So if the runner is coming round each lap (on pace) and calling out 176... 177... then I watch very closely.
Okay, the first few times this happens to runners the coach might be excused for thinking that the runner has suddenly got much fitter. A drop in HR at the same pace is generally taken as a sign that the runner is “working less”, ie: fitter than previously.
Of course that COULD be the case here, but if I also see that the runner is having to work hard to maintain pace, I stop the session. From experience we have learned that when such a situation occurs, (the HR “will not come up”) then it is because the runner has not fully refueled muscle glycogen from a previous training session, or (in some other way) has not fully recovered from previous training.
I often bag the session and send the runner home with instructions to eat more carbos – maybe also just jog easy for a day or two to help refueling/recovery. When we reschedule the same session for 2-3 days later, we often find the HR is higher, but is in the expected HR zone PLUS the runner finds the pace easier to handle.
So, there you are: a low HR is not always a good thing and a higher HR is not always a bad thing.
A lower-than-expected HR is much more likely to be a sign that the runner is under-fuelled, or not fully recovered from previous training. Much the same as a lower-than-usual lactate value at a running pace is not always a sign of increased fitness; it might simply be a sign that the runner is low on muscle glycogen. In both cases (HR and lactate) the runner will often corroborate this by admitting the pace is “harder than usual” on that occasion.
A higher-than-expected HR on a given night is NOT a sign of lack of recovery from previous training. But it can mean the runner is coming down with a cold/infection. It could also mean that he/she did not sleep well enough the previous night. If the runner is otherwise okay, the session might be completed that night, but watch their health for the next few days and get them to make an extra effort to get more sleep.
So, although many coaches will say running pace is king when it comes to designing workout paces, pace alone will not tell you how hard each runner is working on any given day. And ultimately that's more important (to know) than pace.