Heart Rate Variability: A Valuable Tool in Monitoring Endurance Training

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I’ve been using Heart Rate Variability (HRV) to guide endurance training for nearly 20 years. As with every innovation, we do research and test it extensively before we introduce the use with athletes.  I was introduced to HRV by Tiina Hoffman the former skier and coach for the University of Alaska Anchorage. Tiina received  a master’s degree at the University of Jyvaskyla and worked under Heikki Rusko who was integral in the development of the Firstbeat software and introducing HRV to the sports world.  It’s a powerful tool—when used appropriately. But like all tools, it has both strengths and limitations, and understanding those are critical.

In the endurance sports world, there’s no shortage of opinions about the best ways to monitor recovery. Over the last few years, I’ve heard coaches advocate for resting heart rate over HRV (specifically RMSSD), or dismiss HRV entirely as a measure of readiness—a word that is at best inaccurate. A prominent coach in his blog post vehemently disagreed with me, arguing that an Olympic medalist wouldn’t have raced if they’d followed their HRV the day of competition. That kind of logic and thinking reflects a misunderstanding of the autonomic nervous system and the role HRV plays in training and recovery.

The first principle is simple: stress is stress. Physical training stress, psychological strain, emotional upheaval, illness—all of it can impact HRV. That’s why context is everything. We need to interpret HRV data alongside training performance and subjective indicators like mood or perceived exertion. But perception isn’t foolproof—feeling good after an illness doesn’t necessarily mean you’re ready to train. In multiple studies it has been demonstrated that mental fatigue and outside stressors can significantly reduce time to exhaustion in lab testing. Thus, the context that we need to understand all stress as impact our performance.

It’s also important to separate recovery and adaptation. Recovery is necessary to adapt, but adaptation tends to occur when HRV is within or above normal. A single test doesn’t tell us much unless it’s indicating an illness. What matters more are the acute (7-day) and chronic (long-term) trends.

Key Benefits of HRV-Guided Training

• Individualized training response
• Early detection of overtraining or illness
• Improved recovery and adaptation cycles
• Objective confirmation of subjective metrics (RPE, sleep, mood, training performance)

A summary from Team Aker Daehlie web site article and Dr. Hans Kristian Stadheim of the Norwegian School of Sport Sciences:

“Measuring HRV can be a simple and effective tool in assessing whether one is ready for the next training session… HRV is a relatively inexpensive and practical way to monitor recovery and performance readiness. It should not be the sole basis for training decisions, but it can be a reliable indicator of balance and adaptation.”

Consistency Is Key For HRV to be actionable, consistency in measurement is critical. We use a three-minute seated or standing morning test, which places just enough stress on the body to generate reliable stable values. We also recommend use an EKG strap and sensor—optical sensors are far less reliable for HRV due to their dependence on pulse wave analysis.

What HRV Tells Us

1. A stable or slightly increasing HRV indicates a favorable state for adaptation; maybe load can be increased modestly.
2. The 7-day trend gives a more comprehensive picture of how the athlete is handling training.
3. Sudden drops in HRV may signal illness, poor sleep, or external life stress—context is essential.

From experience, resting heart rate can help provide additional insight but is far harder to interpret than HRV. Race day HRV metrics are nearly meaningless due to sympathetic nervous system activation from pre-race excitement and stress. It’s common to see suppressed HRV on race day and the day before.

Case Example A 50-something master skier targeted an “A” race on 2/22/23. Each race day, HRV dropped below normal—but 24–48 hours later, we consistently observed strong rebounds in HRV. Leading into the A race, HRV (measured by LnRMSSD) remained stable or rising during taper. This is exactly what we want.

We use ~3.9 LnRMSSD as this athlete’s baseline. Seven-day rolling trends guide adjustments—sharp drops prompt conversation and potential changes. Over three years, this athlete’s baseline has risen from 3.75 to 4.25–4.5, a sign of long-term adaptation and improved autonomic function.

I’ve worked with many athletes stuck in plateaus—training more but performing worse. Suppressed HRV over weeks to months often signals overtraining or maladaptation, even in the absence of medical or health issues. In these cases, the solution is very easy training until HRV stabilizes. I’ve seen RMSSD values in burned-out athletes climb from 35–40 ms to 100–125 ms over time with appropriate adjustments.

Training Adjustment Guidelines Based on HRV 7-Day Trend

HRV gives us deep insight into an athlete’s physiological state—but we still need to ask why it’s dropping. Not all decreases are training-related. We should also track training output itself. Over several weeks, athletes should see steady performance gains in speed, power, or pace at a given submaximal effort. If that is not consistently occurring something in not working, either in the training, recovery or failure to adapt.

Ultimately, HRV allows us to meet athletes where their adaptation, fitness and performance is currently, rather than wishful thinking sometime down the road the fitness will magically improve. The use of HRV supports more consistent training, healthier long-term outcomes, and more predictable performance. In my experience, HRV-guided training has been one of the most impactful shifts in endurance training over the last two decades. It helps us ensure athletes adapt to training—and are ready to perform in a predictable manner.