Heart Rate (“HR”) gives a neutral, comparable measure of effort that factors in internal (levels of fatigue/recovery, muscle damage etc) and external (weather, terrain, altitude, temperature etc) variations day-to-day.
Pace changes a lot depending on all these factors and HR can be used to check that recovery runs are easy enough and harder sessions are tough enough.
– Estimates (ideally accurate calculations from lab testing) of maximum HR can help with using heart rate zones to keep to differing purposes on runs, in line with a structured and intelligent training plan.
– Analysis of data after races can highlight where mistakes were made, showing at what point a given HR for a given distance became unsustainable.
Also, if a recent similar race had a higher average HR it can indicate that the effort level could have been greater. Often it takes some trial and error to work out where that red line is for different race distances.
Things to be careful about:
– Some athletes become too focused on the real-time feedback from an external sensor like a HRM (or GPS watch) and lose the ability to judge intensity, which is a key skill for all running, especially in ultras.
Even if you find a way to perfectly work out. What HR is sustainable and can adapt this exactly to any new race situation (unlikely, given that other factors also have an effect – see the next point).
What happens if a HRM breaks or runs out of battery and you have no other way to judge your effort? A HRM is just one internal or external tool to incorporate and not the only one to rely on.
– HR only reflects cardio effort, which factors in many things, but not everything. For example, in a hilly race the effort required to run downhill may be low and the HR correspondingly low.
But judgement of how much impact your legs can sustain is also important. What may seem sustainable from a HR perspective may lead to trashed legs later in the race from hammering the downhills.
– Most HRMs rely on a strap around the chest (see photo above), which often chafes. Plus many models take several minutes of running and sweating to settle down after spiking the HR early on. This can be very misleading. And is another reason to be very careful when using HR to adjust your pace.
So it’s important to make sure effort can be judged independently of the HRM. One excellent way to get past this particular problem is to use a HRM attached in a different area of the body.
In my experience this leads to a more accurate measurement. Especially in the early minutes, and no chafing issues. I use a HRM within a cap made by LifeBeam which I’ve found very effective. And its battery lasts for around 15-17 hours in my experience. So it’s suitable for most ultras for most runners. I once tried to use a HRM chest strap in a 100-miler. And it took several months for the scars to heal!
This continuous checking can elevate your stress and effort levels. And it can stop you settling into a rhythm. Although it can be more useful on a very hilly route to avoid spiking the HR on the climbs. Instead, check less frequently just to make sure that your internal assessment of effort is roughly (not exactly to the nearest beat/minute) in line with the external data from the HRM. This is equally valid for the frequency of checking pace via a GPS watch.
– Factor in that using a HRM with a GPS watch will reduce the battery life of the watch due to the bluetooth syncing. Up to marathon distance this is rarely an issue. But it can be essential for ultras where watch battery life is often tested to the limit.
I’ve run with two watches before – one to sync with the HRM in my hat. But with no GPS data, and one purely for GPS. This much data at the fingertips can be a bit of a overload. And I find it most useful for checking infrequently. Then analyzing later on on a computer to see what I can learn for future races.
Ultimately a HRM is just one tool to aid running. And it can help if used in a smart and effective way. However, the factors above show that it can also lead to worse training. And racing (and scars) if not used appropriately.