Heart rate has somehow become the most overtrusted metric in endurance training. Somewhere along the way, it stopped being a tool and started being a referee. Stay in the right zone and you’re doing it “correctly.” Drift out of it and clearly something is wrong with you, your fitness, or your discipline.
I’m not anti heart rate. I use it. I coach with it. I look at trends all the time. But I am deeply skeptical of the way heart rate data is treated as objective truth when it’s filtered through sensors, algorithms, assumptions, and research that never centered the bodies most athletes actually have.
Especially women. Especially masters athletes. Especially menopausal athletes. Especially BIPOC runners.
So let’s actually look at what’s happening instead of letting the watch run the narrative.
How Heart Rate Is Measured (And Why That Matters More Than You Think)
Chest straps and wrist-based watches are not doing the same job.
Chest straps measure the electrical signal of the heart. They sit close to the source, pick up a strong signal, and aren’t easily thrown off by arm movement. That’s why they’re still considered the reference standard in research and why they behave well during intervals, hills, and surges.
Wrist-based watches use optical sensors. They shine light into your skin and estimate heart rate based on changes in blood volume. That estimation is sensitive to motion, temperature, hydration, contact pressure, arm swing, and skin optics. They work reasonably well at rest and during steady efforts. They struggle when intensity changes quickly or movement gets chaotic.
That’s not user error. That’s physics.
Most accuracy claims you see are based on controlled treadmill studies with steady speeds and short durations. Outdoor running does not behave that politely. Wind, heat, hills, fatigue, stoplights, and real pacing decisions all introduce noise that wrist sensors have to smooth, guess through, or lag behind.
And that’s before we even talk about who this tech was designed for.
The Research Wasn’t Built on Women’s Bodies
Women were historically excluded from exercise physiology research because menstrual cycles were considered “confounding variables.” Instead of studying complexity, it was avoided. That choice shaped everything downstream: max heart rate formulas, VO2max protocols, training zones, recovery models, and performance algorithms.
The watches most women gravitate toward are not “female tech.” They’re general devices with menstrual cycle tracking layered on top. The sensor didn’t change. The model didn’t change. The assumptions didn’t change. Logging a period does not suddenly make an algorithm understand hormonal variability, autonomic shifts, or menopausal physiology.
So when a woman’s heart rate behaves differently, the watch doesn’t say, this model may not fit you. It says your fitness dropped, your recovery is poor, or your effort was wrong. Helpful.
For BIPOC athletes, there’s another layer. Optical sensors rely on light interacting with tissue. Skin tone can affect signal quality, particularly during higher-intensity movement. Some studies show minimal differences. Others show increased error with darker skin tones. Results vary, partly because skin tone is often measured poorly and sample sizes are limited. But the takeaway is simple: error is not evenly distributed, and athletes are rarely told that.
Zone 2 Is Not a Number, Fight Me
Zone 2 has been flattened into a heart rate number when it’s actually a metabolic state.
Sustainable aerobic work. Controlled breathing. Conversation possible in phrases. Effort that feels steady and almost boring in the best way.
Heart rate can help confirm that state over time. It should not be the bouncer at the door.
Most athletes obsessing over zone 2 have never done a proper VO2max test. Even fewer have done one that reflects how they actually run outside. Lab VO2max tests are linear, incremental, and designed to push you to failure efficiently. Outside, effort ebbs and flows. You surge, settle, adjust stride, respond to terrain, manage wind and heat.
Add in max heart rate formulas that become less reliable with age, plus hormonal shifts that alter cardiovascular response, and suddenly we’re stacking assumptions on top of assumptions. When the data doesn’t line up, athletes assume the problem is them.
It usually isn’t.
Your Watch Has Lag. So Does Your Training When You Chase It
Let’s talk about the thing almost everyone does and almost no one considers.
Constant wrist checking.
Every time you lift your wrist to check pace or heart rate, you interrupt arm swing, posture, and rhythm. Shoulders tighten. Stride shortens. Flow breaks. Over miles, those small disruptions add up.
At the same time, the optical sensor loses optimal contact. When wrist position changes, signal quality drops. When you lower your arm again, the watch doesn’t instantly recover. It needs time to reacquire the signal and smooth the data.
So you’re reacting to delayed information. Pace lags. Heart rate lags even more. You adjust effort unnecessarily, check again, and repeat the cycle.
Congratulations, you’ve built a feedback loop of overcorrection.
This is why heart rate is a terrible real-time governor and a much better rearview mirror.
Yes, Chest Straps Are Better. No, They’re Not Magical.
At this point, someone is ready to say, “Well my data is clean because I use a chest strap.”
Cool. Chest straps are better at measuring heart rate. They measure the electrical signal directly and reduce sensor noise from movement and optics. If heart rate truly matters for a session, they’re the most reliable option.
But cleaner signal does not mean perfect data.
Chest straps measure electrical timing, not physiology in context. They can tell you when your heart beat occurred, not why your heart rate is elevated, suppressed, drifting, or slow to respond. Stress, sleep debt, underfueling, hormones, heat, illness, and emotional load still influence the data.
Placement and contact matter too. Too loose, too dry, slightly off-center, and you can still get spikes or dropouts. That early-run weirdness many people see isn’t improved fitness. It’s sweat improving conductivity.
Chest straps reduce motion artifact, they don’t eliminate it. Aggressive downhill running, trail scrambling, sharp torso rotation, or chaotic movement can still introduce noise.
They also don’t fix heart rate lag. Heart rate itself is a trailing physiological response. Even with perfect detection, HR responds after effort changes. A strap can tell you exactly when HR increased. It cannot make your cardiovascular system respond faster.
Comfort matters more than people admit. Chest straps can chafe, feel restrictive, irritate skin, or interfere with breathing perception. Many women find them uncomfortable due to sports bra compression or body shape. If wearing one creates tension or distraction, the “clean data” comes at a cost.
And finally, chest straps still feed into biased models. Better input does not fix frameworks built on male-centered research with limited representation of women and BIPOC athletes.
Chest straps are excellent tools. They are not truth machines.
Why I Prefer Effort (And Why That’s Not Anti-Science)
Heart rate reflects stress, not just fitness. Sleep, hydration, fueling, hormones, heat, emotional load, and life chaos all show up. That makes HR incredibly useful for spotting trends and incredibly unreliable as a moment-to-moment judge.
Effort integrates everything in real time. It doesn’t lag. It doesn’t need recalibration. It responds to what’s actually happening right now.
For women, masters athletes, menopausal athletes, and BIPOC runners, effort-based training is protective. It builds self-trust instead of outsourcing authority to systems that may not understand their bodies very well.
This isn’t rejecting data. It’s using data with humility.
How to Use Heart Rate Without Letting It Hijack Your Training
Use heart rate to look at trends, not to micromanage individual runs. Let the watch collect data quietly. Check it sparingly. Review patterns after the run.
Pair heart rate with breathing, posture, rhythm, and perceived exertion. If heart rate drifts, ask why before assuming failure. Heat, duration, fatigue, fueling, stress, and hormones all matter.
Because here’s the quiet truth: when athletes stop interrogating their watch every 30 seconds, they usually run better. Pacing smooths out. Effort stabilizes. Confidence improves. And ironically, the data often looks cleaner too.
Heart rate is a tool. Not a judge. Not a moral authority. And definitely not the final word on bodies it was never designed to understand.
If This Resonates, Here’s the Next Layer
If all of this makes you feel a quiet sense of relief instead of panic, that’s not an accident.
This is why I teach athletes how to train by effort first, with data as support instead of supervision. Effort-based training isn’t about vibes or guessing. It’s a skill you can learn, refine, and trust, especially when heart rate, pace, or conditions don’t behave predictably.
I break this down more practically in Running by Effort: How RPE and VDOT Pacing Work Together, where I walk through how perceived effort and smart pacing frameworks can coexist without turning your watch into a boss fight.
If heart rate data has ever made you feel like you’re failing at training, you’re not broken. You’re just ready for a system that accounts for real bodies, real stress, and real-world running.
I coach athletes using effort-based, trend-informed training that prioritizes sustainability, confidence, and long-term adaptation over chasing perfect numbers. Heart rate becomes context, not control.
If you want to stop outsourcing trust to a device and start training in a way that actually fits your body, you can learn more about how I coach and explore my education resources at hustle.run.thrive.
Frequently Asked Questions About Heart Rate Training
Is heart rate training accurate for runners?
Heart rate training can be useful, but accuracy depends on how heart rate is measured, the conditions of the run, and how the data is interpreted. Wrist-based heart rate monitors are more prone to error during movement and intensity changes, while chest straps provide a cleaner electrical signal. Even with accurate measurement, heart rate is still influenced by stress, sleep, hydration, hormones, heat, and fatigue, so it works best as a trend indicator rather than an absolute rule.
Is a chest strap better than wrist-based heart rate monitoring?
Chest straps generally provide more reliable heart rate data because they measure the electrical signal of the heart directly. However, “better” does not mean perfect. Chest straps still show heart rate lag, are sensitive to placement and contact, and do not account for context like hormones, stress, or recovery status. Cleaner signal does not automatically mean better training decisions.
Why does my heart rate seem high even when my pace feels easy?
Heart rate reflects overall stress, not just fitness. Elevated heart rate during easy runs can be influenced by heat, dehydration, poor sleep, underfueling, cumulative fatigue, hormonal shifts, illness, or emotional stress. This is especially common for masters and menopausal athletes. A higher heart rate does not automatically mean you are training incorrectly.
What is zone 2 training and how should it feel?
Zone 2 is a metabolic state, not a specific heart rate number. It generally feels sustainable, controlled, and steady, with breathing that allows conversation in short phrases. Heart rate can help confirm zone 2 over time, but effort, breathing, and perceived exertion are more reliable real-time indicators than trying to stay under a rigid heart rate cap.
Why does my heart rate lag during workouts?
Heart rate is a delayed physiological response. It rises after effort increases and falls after effort decreases. This lag happens regardless of whether you use a wrist sensor or a chest strap. Because of this, heart rate is not ideal for real-time pacing, especially during intervals, hills, or variable terrain.
Does checking my watch frequently affect my heart rate data?
Yes. Constantly lifting your wrist disrupts arm swing, posture, and rhythm, and it temporarily degrades optical heart rate signal quality. Watches need time to reacquire and smooth data after wrist position changes. Frequent checking can create delayed or fluctuating readings that don’t reflect what’s happening in the moment.
Is heart rate training reliable for women and menopausal athletes?
Heart rate training frameworks were largely developed using male subjects, and they don’t always translate cleanly to female physiology. Hormonal fluctuations, menopause, and aging can all alter cardiovascular response independent of fitness. For many women, heart rate is more useful for observing long-term trends than for enforcing strict training zones.
Do heart rate monitors work differently for darker skin tones?
Wrist-based optical heart rate sensors rely on light interacting with tissue, and research shows mixed results regarding accuracy across skin tones. Some studies suggest increased error during higher-intensity exercise for darker-skinned athletes. This does not make the data useless, but it reinforces the importance of not treating heart rate numbers as absolute truth.
Should I train by pace, heart rate, or effort?
Each has a role, but effort is often the most reliable real-time guide. Pace doesn’t adjust for conditions, and heart rate lags effort. Effort integrates terrain, fatigue, stress, hormones, and environment automatically. Many athletes benefit from using pace and heart rate as reference points while prioritizing perceived exertion during the run.
Is heart rate variability (HRV) more reliable than heart rate?
HRV can offer insight into nervous system stress and recovery, but it is also sensitive to sleep, illness, stress, alcohol, hydration, and measurement consistency. Like heart rate, HRV is best used to observe trends over time rather than to dictate day-to-day training decisions in isolation.