There are a bunch of different ways to measure your training (and recovery). Some of the most common things to measure are rating of perceived exertion (RPE), acute:chronic workload ratio (ACWR), pain, soreness, fatigue, sleep quality, caloric intake, and heart rate variability (HRV). Of these measurable attributes, the only objective one is heart rate variability.
Heart rate variability (HRV) is the time difference between heart beats.
Think about if you have a heart rate of 60 beats per minute. If your heart beats exactly every second, there is no variability. If your heart beat averages 60 beats in the minute, but the time between beats changes by a lot, you will have a higher heart rate variability.
Bear with me here...The heart rate and rhythm is controlled by the autonomic nervous system. The parasympathetic nervous system uses vagal stimulation, while the sympathetic nervous system uses epinephrine and norepinephrine to affect the heart rate. There is constant interaction between the parasympathetic and sympathetic systems.
Increasing HRV = More vagal stimulation
Decreasing HRV = More SNS (fight or flight) stimulation
It is well known that there are correlations between having a lower HRV and health complications like heart attack, stroke, heart failure, pain, poor sleep, and poor diet. There is evidence emerging more recently looking at links between lower HRV and musculoskeletal injury. This link is likely from the increased SNS response causing inflammation.
Decreasing HRV can be seen before any symptoms present. HRV can help us be proactive in mitigating injury risk, whereas pain and stiffness are retroactive. It’s better if we can acknowledge a trend in HRV decreasing to make the necessary changes to avoid an injury. A reduction in HRV combined with an increase in training volume has been associated with a “very likely” probability of reporting an overuse injury in the following week.
Improving HRV is done by improving parasympathetic input to your system. This can be done via improving sleep quality (8+ hours without waking), better dietary behaviors (increased fiber and protein), long and slow aerobic recovery sessions (conversational RPE), and bodywork/physical therapy.
Wearable technology has been keeping up with the research, and there are a variety of apps and devices you can use to measure HRV. Here is a brief list:
I won’t get into the specific differences between all of the different trackers, but the most common ones are HRV4 Training ($9.99 one-time fee) for app-based tracking and WHOOP ($15-30 per month) for wearable tracking. WHOOP has become the gold standard for measuring HRV and tracking recovery.
What doesn’t get measured, doesn’t get changed.