Introduction
When coaching athletes from a distance (and that’s pretty much all of them right now), HRV is an especially useful tool with which to gauge an athlete’s current recovery status, adaptation to training and ability to cope with their prescribed training load. However, as with any measure, garbage in = garbage out. As such, it’s very important to make sure the athlete is set up in the right way to capture high-quality data that informs decision-making. In this article, we will cover the most important elements for them to focus on in order to get an accurate and helpful reading.
Equipment
Sensor
Traditionally, because it is based on the precise measurement of inter-beat intervals, HRV was always measured using a medical-grade ECG. A Bluetooth HRM chest strap is the sport-friendly equivalent of the ECG, and current products from well-known brands such as Polar, Wahoo and Cardiosport have been validated for HRV use. The small print here is that the strap must be in good condition, and the skin contacts well moistened either with water or saline before taking an HRV reading to avoid artifacts that can distort the HRV reading (often making it higher than the true value). The strap part should be washed every month and replaced every year to avoid problems.
In the past five years, a few consumer pulse sensors on the market have also been validated as accurate enough for HRV. Several of these use what’s called transmission photoplethysmography through the arteries in the fingertip to accurately detect the pulse. I’ve also evaluated a large number of wrist-based devices based on reflection PPG, and have not yet found one that is accurate enough for HRV. This is because there is simply not sufficient blood flow on the back of the wrist to detect HRV accurately.
App
Most athletes will track their HRV using an app. The number one consideration here is that the app has been independently validated for accuracy by a university or other competent institution. If in doubt, contact the app manufacturer and ask for this information.
It’s also highly desirable that the app connects to a cloud service that provides in-depth analysis, provides secure storage of the athletes’ valuable data, and interfaces to your preferred training software (like TrainingPeaks!)
Taking the Measurement
Time of Day
Like other biometric measures such as blood pressure, HRV varies throughout the day. It’s important to standardize a time window (of about an hour) to prevent unwanted variations in readings. The first thing in the morning is the best time—before consuming food, caffeinated beverages, email or social media.
Position
Owing to their lower resting heart rate, it is strongly recommended that endurance athletes take HRV readings with the upper body upright. Readings will vary depending on the position, so it’s best to choose either sitting or standing and stick to it. If an athlete’s resting HR is in the mid-50s bpm or lower when sitting, I would recommend standing.
Breathing & Relaxation
It’s important to feel relaxed when taking an HRV reading, as anxiety will almost certainly lower the measured HRV from its true value. A lot of people find a slow breathing pattern relaxing. This has the added bonus of standardizing breathing rate and depth, both of which have a significant influence on HRV.
Establishing a Baseline
Nearly all HRV software builds a long-term average of the daily readings to use as a baseline. It is from this baseline that we can drive trends and make appropriate recommendations. It’s best to start using HRV in a period of light loading or in the offseason so that the baseline is most representative of the athlete’s recovered state.
Recording Context
Although HRV is a sensitive indicator of stress and recovery, you need context to interpret it. It’s vital to make this data actionable. Effective software will allow the user to capture subjective feel (overall fatigue, soreness, mood) and recovery enablers (sleep quality, stress management, diet). The best apps even allow you to flag days where the athlete was sick or on medication, underwent travel stress and, for women, dates in the menstrual cycle. It also helps to display training loads and derived metrics (TSB, Acute-to-Chronic Load Ratio, etc.) alongside the daily HRV and trend data.
