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.