Or rather, I don't know if it is or it isn't. You see, for the last few weeks I've been running without a heart rate monitor; initially because it wasn't working properly and the data I was seeing was bonkers, and then without bothering to wear it at all.
To give a bit of background, round about November 2016 I jumped feet first into training by heart rate: first, by loosely following Phil Maffetone's theory, and then actually working out my zones (approximately) using the Friel protocol. I had my watch set-up to display my HR as the primary field, rather than pace as might normally be expected; my theory was that, as my friend Owain said (though claims not to remember!), the body doesn't distinguish between stresses. What constitutes an easy day can change depending on a variety of factors: sleep (or lack thereof), work stresses, weather conditions, terrain etc.
I was mainly focused on training for ultras at this point, so I was pretty much running long, slow, and with a tonne of vert. My plan was to keep my HR under 148bpm (coincidentally, both my MAF number and the upper limit of zone 1 according to Friel) and if that meant walking, well, so be it; there's nothing wrong with the odd tactical hike in an ultra. The first few weeks I literally couldn't run up an incline at that heart rate but that soon resolved itself and, whilst I still had to slow significantly, I was able to maintain a legitimate running gait.
What did all of that tell me? Basically, for the few years previously I'd had no idea what 'easy' actually meant! Aerobically, I was underdeveloped. I hadn't been doing any actual speedwork, but every run I went on I tried to PB. I was running too hard for easy, and too easy for hard, occupying that grey area of neither recovering nor developing.
Unfortunately, it seems that the Suunto SmartSensor belts are not the most robust pieces of equipment and, having got only 330 hours use out of my second(!) one since 2016 before it started giving me utterly bonkers readings, I decided to ween myself off it on the basis that I didn't want to keep buying new ones! Since starting to train with Tynedale Harriers, and also reading Jack Daniels' Running Formula, I've begun working to pace far more anyway, particularly for workouts. I used to say that running with an HRM kept me honest, in that I couldn't kid myself that I was running easy when I wasn't. Having now trained myself to recognise that feeling - rate of perceived effort, as they say - the HRM is largely unnecessary.
So what difference, if any, has it made? It's still early days but, other than no longer having patches of eczema on my chest from the strap, it's largely had no effect. I do have to make a conscious effort to hold back at times on easy days, but I recognise that and act accordingly; a much more holistic approach! Hard days it hasn't affected at all, and the only thing I miss is geeking out over/laughing at the data and charts from VO2max workouts and races. My watch now thinks I'm permanently overtrained, but I'm confident that that isn't the case based on old data; I know that a 50 minute 10k is not pushing my system to a PTE of 5.0, whatever it says!
A useful experience, and I'd recommend to everyone who runs to learn how to use, and then experiment with, a HRM at some point. If the kit was more robust, I'd still be using it now, just 'cause. That said, at the risk of some kind of confirmation bias, feeling what is easy and what's hard does seem far more useful than being a slave to numbers.