Indicators of Fitness And Readiness
HRV is the key metric that determines my fitness and training readiness. Heart rate variability measures the time between each heartbeat. Somewhat counterintuitively, for me, more variance between beats is better. A higher variability indicates better cardiovascular fitness and a more resilient, balanced nervous system. I take mine each morning using a simple iThlete finger sensor, which downloads the information into my iPhone and an online dashboard in less than a minute.
During exercise, the sympathetic nervous system – the ‘fight or flight’ response – ramps up. We also have a parasympathetic system responsible for ‘rest and digest’. A higher HRV indicates the latter system to be more dominant, suggesting better recovery, lower stress, and better resilience.
It’s an excellent indicator for me as to the level of training I should undertake and, indeed, if I should train at all. I did a little too much last week, and by the end of my run yesterday, I was feeling tired. But my reading this morning showed me to be well recovered, so I know I can safely train. Gut feel is good, but you cannot beat concrete measures.
It’s not just about fitness, either. I know that during my periods of stress and anxiety, my HRV would drop, too. My fight-or-flight system overpowered my relaxation, rest, and sleep. It can also indicate oncoming colds and viruses. I had COVID a couple of years ago, and my morning HRV told me something was up before a nasal swab confirmed it. We have all pushed the training a touch hard when we felt a cold coming on and later regretted it. A quick check of your HRV can turn a ‘feeling’ of unwellness into a solid indicator that you can act upon.
Ready To Roll?
The image on the right shows my reading from today. Yesterday, my score was below 70, and the number had turned red, which indicates a period of low resilience. Today, I’m back into my normal range—mid-70s to low 80s—and the number has turned green. I’m good to go. I am well rested, and my fitness is in a good place.
From a macro view, a high HRV shows a body that can adapt to changing demands and stressors, whether from hammering out the miles or dealing with the stresses of life.
It’s also a marker of good heart health. My normal range shows me to be in good cardiovascular health, as confirmed by my ECG treadmill test and blood metrics in my recent medical.
Several studies show that people with higher HRV tend to have better overall fitness, better mental health, and even greater longevity. I know that VO2 is an excellent indicator of fitness and the potential for a better health span, but the cost and availability of the required kit are prohibitive. I use a £35 sensor and pay £30 a year for the whole iThlete setup, whereas a VO2 monitor runs into the thousands of pounds.
HRV is a key metric that enables us to assess fitness, recovery, and even mental health and stress levels.
Actionable Information
The beauty of a one-minute measurement each morning is that it can enable you to amend your activity for the day accordingly. I will smash the exercise if I’m over 80 and green on my score. Green and 70s will see me do my regular workout. With a score of under 70, or if the number has turned red, I will more often than not scrap training for the day. Here’s a simple indicator enabling you to adapt to how your sympathetic and parasympathetic systems feel using actual data. You don’t need an expensive coach to tell you to crack on or back off. TrainingPeaks has a great article on adapting training here, and it has links to some top-notch performance trials at the foot of the page.
I use a finger sensor because I feel it gives me a more accurate read. But it’s worth noting that wearables such as WHOOP, Fitbit, Apple, and Garmin watches also deliver a daily score. One important point to note is that various devices use different scales. The table above shows the other scales used = Apple watches and the like use rMSSD, shown in the first column. They are all valid, and as long as you take action when you see scores drift out of range, then it’s all good.
HRV is the key metric in my experience, and it’s an easily accessible measure for weekend warriors.