Wearable technology has changed sport culture, especially in the last 10 years. Athletes now track resting heart rate, sleep, recovery scores, and heart rate variability with the same intensity they track pace, mileage, and power. Many coaches use HRV trends to guide training decisions, adjust intensity, and improve periodization. In theory, this sounds like progress. But there’s a growing problem: athletes are increasingly trusting wearable data as objective truth, even when their bodies are clearly telling a different story. And in the context of Relative Energy Deficiency in Sport (REDs), this disconnect matters. Because HRV for athletes reflects autonomic balance, not health. In underfueled athletes, heart rate variability patterns can falsely resemble “excellent recovery” while masking metabolic suppression. In this blog post, we dive into what heart rate variability measures, when wearables mislead, and how REDs distorts recovery data.
Why HRV for Athletes Has Become a Performance Obsession
HRV in athletes has gained popularity for a reason. It offers a window into autonomic nervous system regulation, and in many cases it can provide useful insight into training stress.
Many coaches use heart rate variability to:
- Monitor adaptation to training loads
- Adjust intensity during high-stress weeks
- Reduce risk of overtraining
- Improve performance outcomes through smarter periodization
Wearables have made HRV more accessible than ever. Athletes don’t need lab testing or clinical evaluation, they can wake up, check a score, and assume they’re getting real-time feedback about recovery.
But the promise of HRV has also created a false sense of certainty.
And just like we discussed in the previous post on low resting heart rate for athletes, numbers that look “elite” can sometimes reflect suppression rather than true adaptation.
What Heart Rate Variability Actually Measures (and What It Doesn’t)
Heart rate variability is an indicator of autonomic nervous system modulation. In simple terms, HRV reflects the balance between:
- Sympathetic activity (“fight or flight”)
- Parasympathetic activity (“rest and digest”)
When used well, heart rate variability and recovery trends can help athletes and coaches identify when training stress is accumulating.
But HRV is not a direct measure of:
- Nutritional adequacy
- Hormone health
- Metabolic resilience
- Cardiovascular integrity
This distinction matters because HRV is easily influenced by survival physiology.
In REDs, the nervous system doesn’t simply “recover better.” It often downregulates, and downregulation can look deceptively calm.
Why High Heart Rate Variability Isn’t Always a Sign of Recovery
One of the biggest misconceptions in sport is the assumption that higher HRV automatically equals better recovery.
Sometimes it does. But HRV is not inherently “good” or “bad.” It’s a signal, and signals require interpretation.
In a well-fueled athlete, parasympathetic dominance can reflect:
- Strong cardiovascular adaptation
- Effective recovery
- Adequate energy availability
In an underfueled athlete, parasympathetic dominance may reflect:
- Autonomic suppression
- Metabolic conservation
- Reduced physiological resilience
The HRV number might look impressive, but the context is entirely different.
This is one of the reasons athletes can become trapped in a cycle where wearable data reinforces training behavior, even as the body becomes increasingly depleted.
How REDs Distorts Heart Rate Variability and Recovery Trends
In REDs, the body is not optimizing performance. It is conserving energy.
To do this, it may reduce metabolic rate, suppress endocrine function, and shift autonomic regulation. This downregulation can influence heart rate variability and resting heart rate in ways that mimic elite conditioning.
This is why HRV can become one of the most misunderstood metrics in underfueled athletes.
A common pattern looks like this:
- Resting heart rate continues to fall
- HRV appears “high” or stable
- Wearable recovery scores remain positive
- The athlete feels increasingly fatigued, cold, flat, or unmotivated
- Sleep becomes disrupted
- Training performance plateaus or becomes inconsistent
The watch says “recovered.” The body says “depleted.”
This pattern fits into the broader physiology of underfueling in athletes, where survival adaptations can emerge long before performance collapses.
Nocturnal Bradycardia: When Wearables Become Misleading
This pattern is illustrated clearly in a common clinical scenario:
An athlete reports a daytime resting heart rate around 41 bpm. Within their training group, this number is treated as a marker of competitiveness and superior fitness.
They wear a smartwatch overnight to track HRV and recovery. On several occasions, the device alerts them during the night to heart rates dropping into the 30s.
Rather than feeling concerned, the athlete interprets this as a positive sign, proof that training is “working.”
But additional symptoms begin to emerge:
- Sleep maintenance disruption
- Cold extremities
- Purplish discoloration of hands and toes
- Increasing fatigue
These signs are often dismissed as environmental (air conditioning, weather, stress). In reality, they can reflect compromised circulation and physiological suppression.
This is one of the most important takeaways for athletes and clinicians: Wearables can capture data, but they cannot interpret physiology.
The Overlap Between REDs and Overtraining Syndrome
HRV is often discussed in the context of overtraining syndrome, and for good reason. It can help identify maladaptation and inadequate recovery. But REDs and overtraining are deeply intertwined.
Many athletes who present with overtraining symptoms are also experiencing low energy availability. In these cases, the nervous system isn’t just responding to training stress, it’s responding to an energy deficit.
This is why increasing rest days alone doesn’t always resolve the issue.
If the underlying problem is underfueling, the body cannot fully recover, even if training load is reduced.
When Wearable Recovery Scores Become a Problem (Not a Tool)
Wearables are not the enemy. But they become harmful when athletes begin prioritizing numbers over symptoms.
In REDs, wearables can become misleading in several ways:
1) Athletes ignore symptoms because the watch says they’re “fine”
Fatigue, sleep disruption, cold intolerance, mood changes, and plateaued performance may be brushed aside because HRV looks “good.”
2) Recovery scores become permission to train harder
Instead of guiding recovery, the wearable becomes justification to increase volume or intensity, often worsening the underlying energy deficit.
3) Athletes confuse suppression with fitness
A low resting heart rate and high HRV can be interpreted as elite conditioning, when they may reflect a downregulated nervous system.
This is why data must be contextualized.
Wearables can inform decision-making, but they should never override how your body feels.
How to Interpret HRV for Athletes: Context Over Metrics
When evaluating heart rate variability and recovery trends, context matters more than the number.
Important context includes:
- Fueling consistency and energy availability
- Endocrine status (especially thyroid and sex hormones)
- Sleep quality and sleep maintenance
- Training load changes
- Symptoms like cold intolerance, fatigue, or decreased libido
- Performance trends over time
Autonomic changes don’t occur in isolation, and the same survival adaptations that influence HRV can also alter lab values, especially cholesterol.
What This Means for Athletes
If your HRV looks “good” but you feel:
- Chronically fatigued
- Cold
- Disrupted in sleep
- Flat in training
- Stuck in a performance plateau
…your wearable may be reflecting nervous system suppression, not true recovery.
Data should support decision-making, not override what your body is telling you.
What This Means for Clinicians and Coaches
Interpreting heart rate variability requires more than a recovery score. It requires integration.
In REDs, HRV trends must be interpreted alongside:
- Nutrition and energy availability
- Endocrine markers (T3, estrogen, testosterone)
- Metabolic function
- Cardiovascular signs and symptoms
This systems-based approach is the foundation of how I train clinicians and coaches inside the REDs Informed Provider Certification Program®, where we focus on early identification, integrated interpretation, and evidence-informed recovery strategies.
And for professionals who want continued case-based education, ongoing support, and monthly CEUs, the REDs Performance Mastermind provides continued training across complex athlete presentations.