Is your heart rate monitor working for you or against you?

I am often asked by clients about heart rate and exercise; specifically, how high their heart rate should be when they train. The answer depends on many factors, so I thought it’d be good to take a look at some of these in this post.

Before I continue though, I should add that, if you are advised by a doctor to use a heart rate monitor while you exercise, you should follow their advice regarding exercise intensity. Also, heart rate monitoring may not be the best way to gauge exertion if you are using medications that alter heart rate response, so be guided by your doctor when considering which intensity to train at.

Heart rate monitors have been around in mainstream fitness since the mid-80's and have revolutionised the way that exercisers, be they athletes or recreational gym goers, monitor their exertion and performance. Monitoring systems have evolved from simple devices that consisted of a chest strap transmitter and wrist watch display, to wearable technology, the more advanced of which can also measure other parameters such as blood oxygen saturation. And when used correctly, these systems can be an excellent training tool and provide very useful post-training data which, in the right hands, can be used to optimise training performance.

But reliance on heart rate-monitoring alone may not always be the best way to gauge exercise intensity and, as a result of one simple formula that’s now embedded into fitness culture, could lead to less than optimal training load.

The formula in question is the time-honoured ‘220 minus age’ calculation, the most commonly used to estimate maximum heart rate - a number that's essential when estimating the correct training zones for a given training goal. E.g. when using the formula for a 40 year old, their theoretical maximum heart rate (MHR) would be calculated as 220 - 40 = 180 beats per minute (bpm). This number can then be used to calculate a training zone, usually based on 55 to 85% of MHR, with the lower end (55 to 70%) being termed low to moderate intensity or, somewhat misleadingly, ‘fat burning’. And the higher end (70 to 85%) being moderate to high intensity - sometimes shown as the 'fitness' range on training charts and exercise machines. In reality though, the true maximum heart rate could deviate significantly from the 220 - age calculation, as this article from the New York Times sets out, together with some interesting history on the foundations of the formula.

But not knowing your true MHR makes calculating the heart rate training zones a bit hit-and-miss. And unless you’re prepared to undergo very uncomfortable testing under strict laboratory conditions, finding your actual MHR is practically impossible.

Heart rate monitoring is a great way to track you exercise intensity, but is no substitute for listening to your own body.

So how can you ensure you’re training optimally if you are set on using a heart rate monitor, even if you are unsure of your true maximum heart rate? Well, it probably comes down to a combination of technology and more traditional methods of gauging exercise exertion.

Before heart rate monitors became popular, more simple methods of monitoring were adopted by fitness professionals to ensure their clients were training within the correct limits for their particular goals. These were namely the Talk Test, and the Borg scale for ‘Rate of Perceived Exertion’, or RPE.

The Talk Test consists of simple monitoring of an exercisers ability to talk whist training: Being able to easily hold a conversation whilst exercising would indicate a low level of exertion, and possibly lower than optimal training load; being able to talk with a moderate degree of difficulty would indicate a moderate to high level of exertion and most probably an ideal training load; whilst being unable to talk, or just getting the odd word in here or there would suggest a very high level of intensity which would not be maintained for a long period. Very high levels of intensity might be useful for training optimal performance or interval training, but not suitable for all exercisers, especially beginners or those with certain health conditions.

The Borg Scale on the other hand, relies on the exerciser grading their perceived level of exertion (RPE) by using a scale of 6 to 20 (or simplified by some as a scale of 1 to 10); with 6 being no exertion at all, and 20 being maximal exertion. For most, a grade of 12 to 14 would be considered an ideal range for steady-state training, or if simplified, a 6 or 7 out of 10.

So with the talk test or the Borg scale being used as primary methods to estimate training intensity, the heart rate monitor can now employed as a secondary tool to record heart rate ranges that correspond to this; i.e. once an exerciser has reached a moderate level of intensity on the talk test, the corresponding heart rate can be noted and then used by the exerciser in future training sessions to ensure they are working at the correct intensity for their goals. Further exploration at higher and lower intensities could create a sensible training zone.

Having used this method with my own clients, it's clear that the 220 minus age formula really doesn't work for all: There is often variation from client to client, with some being able to easily exceed the standard HR training zones calculated using this formula whilst still reporting more moderate levels of perceived exertion. The opposite can also occur, where higher levels of exertion are reported relative to those suggested by their heart rate. By keeping records of heart rate and corresponding RPE/Talk Test results during sessions, I can also use heart rate monitoring far more effectively with my clients.

So while wearable tech is great, and makes exercise more interesting for many, heart rate alone may not always be the best way to gauge how hard you're working. Sometimes just listening to your own body can be your best friend here.

Thanks for reading,

Dylan