Why Your HRV Is Low on TRT (Normal HRV by Age for Men)

You check your Whoop or Oura every morning and the number is always the same story: 25, 27, maybe 31 on a good night. Your mates post screenshots in the 60s and 70s. You're on a sensible TRT dose, you train hard, you eat well, and your recovery score keeps telling you you're under-recovered. So is the TRT doing it? Is 25 actually low? And should you care?

The short version is that "low HRV" means very little until you know three things: how old you are, which device measured it, and what your own baseline looks like. Below you'll find the age norms, why your device's number may not match any chart, and what actually pulls HRV down on TRT and on cycle.

What HRV actually measures

Your heart doesn't beat like a metronome. At 60 bpm the gap between beats might be 0.95 seconds, then 1.04, then 0.98. Heart rate variability is the size of that wobble. Most of the beat-to-beat wobble comes from the vagus nerve, the brake pedal of your nervous system, so a bigger wobble at rest usually means the brake is working well.

The problem is that "HRV" is not one number. There are two common measures and they are not interchangeable:

• RMSSD (root mean square of successive differences) looks at the change between each beat and the next. It mainly tracks vagal, rest-and-digest activity. Whoop, Oura, Garmin, Polar and Fitbit build their overnight HRV on RMSSD.
• SDNN (standard deviation of all the beat intervals) captures total variability, including slower swings from blood pressure control, breathing and the day-night cycle. It grows with recording length, so a 5-minute SDNN and a 24-hour SDNN are different quantities (Task Force, 1996; Shaffer and Ginsberg, 2017). Apple Watch reports SDNN from short spot readings taken at random times of day.

That means an Apple Watch reading of 40 and an Oura reading of 40 are not the same 40. And an overnight wearable average, taken while you're asleep and vagal tone is at its highest, will usually read higher than a 5-minute daytime test in a clinic.

How accurate are wearables for HRV?

Reasonably, for the better devices, but not well enough to read one night as gospel. A 2025 study compared five wearables against a chest ECG across 536 nights (Dial et al., 2025). Average error for overnight HRV was about 6% for Oura Gen 4, 7% for Oura Gen 3, 8% for Whoop 4.0, 10.5% for Garmin and 16% for Polar. Resting heart rate was much more accurate on the four devices tested for it, around 2 to 3% error. It was a small study, 13 adults, but the pattern is consistent. A smaller study found the same pattern: Oura and a phone app with a chest strap did well, a camera-based finger app was useless (Stone et al., 2021).

A 6 to 10% error on a reading of 25 ms is 2 to 3 ms either way. That's about the same size as a real day-to-day change, which is why single nights are noise and trends are signal.

Normal HRV by age for men

The cleanest male reference data come from the KORA cohort in Germany: 1,124 healthy men, each given a 5-minute ECG lying down after 5 to 10 minutes' rest, with anyone on heart-rate-affecting drugs or with heart disease excluded (Voss et al., 2015).

Three things stand out in this table. (The spread column is the average plus or minus one standard deviation, a rough guide rather than a strict normal range, since HRV data are skewed.)

HRV falls hard with age, then levels off. RMSSD drops by roughly half between your late 20s and your late 50s. A 24-hour study across nine decades found the same: RMSSD fell to about 47% of its teenage level by the sixth decade, then stabilised (men and women combined) (Umetani et al., 1998). Comparing yourself at 45 to a 28-year-old's screenshot is pointless.

The spread is huge. At 35 to 44, healthy men ranged from the mid-teens to about 50 ms. Part of that is genetic. In Framingham siblings, genes explained 13 to 23% of the variation in HRV (Singh et al., 1999), and twin studies put heritability of the vagal component at 40 to 55% (Kupper et al., 2005). Some healthy men simply run low their whole lives.

This is daytime data, not overnight data. These are 5-minute supine clinic readings. Overnight wearable values usually run higher, and there is no validated conversion between the two. Treat the table as a rough map of where you sit, not a pass or fail line.

Is an HRV of 25 bad? What about 37 or 40?

People search these exact numbers a lot, so here are straight answers from the table above. They assume an overnight RMSSD from Whoop, Oura or Garmin.

• 25 ms at age 30: below the average of about 40, but still inside the normal spread. Worth looking at the suspects below, especially sleep, alcohol and training load.
• 25 ms at age 45: right on the average of 23 for a daytime reading. Since overnight readings usually run higher, you're probably sitting a bit below the middle, which is nothing alarming on its own.
• 25 ms at age 55: above the average of about 20.
• 37 ms: a little above average at 35 to 44, well above average for 45 and over.
• 40 ms: about average at 25 to 34, comfortably above average for every age band after that.

None of those numbers is abnormal for a healthy adult man. What would be meaningful is a number well below your own usual range that stays there.

Why HRV runs low on TRT

Here's the part that surprises most people: there is no randomised trial showing that testosterone replacement at normal doses lowers HRV. The little evidence there is points the other way. In one small study, young men with untreated congenital hypogonadism had lower HRV than matched controls on 24-hour monitoring (SDNN 147 vs 194 ms) (Ermis et al., 2010). That is one study of 22 men with a rare condition, and the mechanism is unknown, so don't read too much into it. But it is hard to square with the idea that bringing testosterone back to normal wrecks HRV.

So if your HRV is low on 100 to 200 mg a week, testosterone itself is not the first thing to blame. These are the things that usually sit underneath it, roughly in order of how often they're the answer.

1. A higher resting heart rate

HRV and heart rate are mechanically linked. The faster your heart beats, the less room there is between beats to vary. A large study across humans, animals and isolated heart cells found HRV is "primarily dependent on heart rate" and that a lot of what people read as nervous-system change is really heart rate change (Monfredi et al., 2014).

That makes resting heart rate the first number to check when HRV looks low. Anything on your protocol that pushes resting heart rate up will drag HRV down with it, even if your nervous system is fine. If your resting heart rate sits in the high 60s or 70s, a low-ish HRV is expected. See our zone 2 heart rate article for what raises resting heart rate on cycle.

2. Haematocrit and blood pressure

TRT raises red cell mass, and thicker blood makes the heart work harder. There's no direct study of TRT-induced erythrocytosis and HRV, so this is a plausible link rather than a proven one. The closest evidence comes from people with a genetic form of high red cell mass: their baroreflex sensitivity, the reflex that steadies blood pressure beat to beat, was less than half that of controls (7 vs 16 ms/mmHg), and their SDNN was lower (Pruter et al., 2023).

Blood pressure works the same way. Low HRV tends to come before high blood pressure, and bringing risk factors down goes along with higher HRV (Thayer et al., 2010). If your haematocrit has crept toward 0.50 to 0.52 and your systolic blood pressure sits in the high 120s or above, both are reasonable suspects. Our guides on lowering haematocrit on TRT and lowering blood pressure on cycle cover what to do about each.

3. Sleep apnoea

Most people miss this one. In a randomised trial in 67 obese men with severe sleep apnoea, 1,000 mg testosterone undecanoate injections every 6 weeks made night-time oxygen drops worse by about 10 events an hour at 7 weeks compared with placebo. By 18 weeks the difference was no longer significant (Hoyos et al., 2012). That doesn't mean TRT gives you apnoea, but if you already have it, TRT can make it worse for a while, and every apnoea event is a jolt to the stress side of your nervous system right in the window your wearable measures. Repeated drops in night-time oxygen are also a known driver of higher haematocrit, so the two often show up together.

Signs worth acting on: loud snoring, a partner who notices you stop breathing, waking unrefreshed, daytime sleepiness, a thick neck, or a haematocrit that keeps climbing on a stable dose. A home sleep study is cheap and settles it.

4. Heavy lifting

Lifters don't get endurance-athlete HRV, and they shouldn't expect to. A single resistance session lowers vagal activity more than an aerobic session does, and resistance training on its own doesn't seem to raise resting HRV in healthy young adults (Kingsley and Figueroa, 2016). A hard leg day will usually show up in that night's number. Endurance athletes with HRV in the 80s and 90s got there through hours of aerobic work, not genetics alone.

5. Alcohol

The easiest one to test yourself. In 4,098 Finnish workers tracked over nights with and without drinking, alcohol cut the HRV-based recovery score in the first three hours of sleep by 9.3, 24.0 and 39.2 percentage points at low, moderate and high intake (Pietilä et al., 2018). Even small amounts showed up. Two weeks dry will tell you how much of your low number is the beer.

What about estradiol?

Human evidence linking estradiol in men to HRV is too thin to draw anything from. If E2 is affecting you, it's more likely through blood pressure and water retention than through any direct HRV effect.

What each compound does to HRV and resting heart rate

Past replacement doses the evidence gets clearer, at least for some compounds.

Supraphysiological steroids

Four separate studies of steroid-using lifters found the same pattern. In 15 bodybuilders on long-term AAS compared with 15 natural bodybuilders and 15 sedentary men, users had more sympathetic and less vagal modulation than both groups, higher blood pressure, and their sympathetic shift tracked with blood pressure and heart wall thickness (Barbosa Neto et al., 2018). Recreational users averaging about 410 mg a week had lower RMSSD, SDNN and total HRV power at rest (Maior et al., 2013). Users had lower baroreflex sensitivity in a second Brazilian study (dos Santos et al., 2018). And in 40 users compared with 40 natural strength athletes, baroreflex sensitivity was 13.8% lower and left ventricular mass 8.9% higher, with early signs of a stiffer heart that worsened with years of use (Kouidi et al., 2021).

These studies have weaknesses. They're small, cross-sectional and the users were running stacks, so no single compound can be blamed. But the direction is consistent, and these are blast doses, several times a TRT dose. That's the gap between "TRT doesn't hurt your HRV" and "cycling does". Our TRT and heart attack article makes the same distinction for cardiovascular risk.

Does it come back after you stop? Nobody has measured that in humans. In rats given nandrolone decanoate for 8 weeks, the loss of vagal tone had not normalised by the end of the study, about 6 weeks after the last dose, even though the ECG changes had (Marocolo et al., 2018). Rats aren't people, but it's a reason not to expect your HRV to bounce back the week your blast ends.

Trenbolone

There is no study of trenbolone and HRV, human or animal. Anyone telling you tren "destroys HRV by X%" is reporting their Whoop, not data. What's plausible is that tren adds to the general AAS shift above, and that its well-known effects on sleep, night sweats and resting heart rate show up in overnight numbers. That's inference, not evidence.

Clenbuterol

No study has measured HRV on clen either. What exists is a systematic review of 24 athletes in case reports, with doses from 20 micrograms to 30 mg a day, showing supraventricular tachycardia, atrial fibrillation, heart muscle injury and heart attacks (Kumari et al., 2023). As a beta-2 agonist, clen raises heart rate, and per the Monfredi finding above, that alone will pull HRV down.

T3 and excess thyroid hormone

This is the best-evidenced compound effect on HRV. A meta-analysis of 22 studies, 1,002 hyperthyroid patients and 9,809 controls found lower RMSSD, SDNN and total power and a shift toward sympathetic dominance (Brusseau et al., 2022). The effects in mild (subclinical) hyperthyroidism were about half those in full-blown hyperthyroidism, and higher thyroid hormone levels tracked with faster heart rates. T3 on a cut should produce a similar state: suppressed TSH, high free T3, faster heart rate, lower HRV. See our thyroid on steroids article for how to read those markers.

Caffeine and stimulants

Caffeine gets blamed for a lot, but the trials don't back it up for resting HRV. In 16 male cyclists given 5 mg/kg of caffeine, resting heart rate didn't change and RMSSD during light exercise went slightly up (Glaister et al., 2025). A meta-analysis found no effect on HRV after exercise at doses of 2 to 6 mg/kg (Almeida et al., 2024). What hasn't been tested is late-day caffeine and overnight HRV, which is where it most likely matters, through worse sleep. Ephedrine and pre-workout blends have no HRV data at all.

Growth hormone and GH peptides

In adults with GH deficiency, 12 months of GH replacement lowered SDNN in 90% of patients while RMSSD didn't change. Their SDNN had been unusually high to start with, so the authors read this as sympathetic tone returning to normal, not as harm (Tanriverdi et al., 2005). Another group found untreated GH-deficient adults had unusual HRV that looked normal on long-term replacement (Leong et al., 2001). Those are replacement doses in deficient patients.

For the GH secretagogues, ipamorelin, CJC-1295 and MK-677, nobody has measured HRV. That includes the common habit of dosing right before bed, which puts the GH pulse squarely in the window your wearable measures. If you run them and want to know, the only way is your own data: a few weeks of baseline, then start the peptide and change nothing else.

GLP-1 drugs

A 2026 meta-analysis of 12 trial reports in people with overweight or obesity and no diabetes put the average heart rate rise at 2.4 bpm for liraglutide, 3.4 for semaglutide, 2.1 for tirzepatide, 3.5 for retatrutide and 7.3 for orforglipron (Zhang et al., 2026). In a post hoc analysis of a randomised trial in 62 people with type 2 diabetes, liraglutide raised daytime heart rate by 5.4 bpm compared with glimepiride but didn't change SDNN, RMSSD or the frequency measures (Nyström et al., 2019). So expect a small dip from the heart rate rise and not much more. Our retatrutide bloodwork guide covers heart rate monitoring on it.

Worked example: 25 ms on 150 mg a week

Take a 44-year-old man on 150 mg of testosterone enanthate a week, split three times. He lifts five days a week, does little cardio, and his Whoop has averaged 25 ms for months. His recent numbers: haematocrit 0.50, up from 0.46 a year ago; resting heart rate 67 to 68; blood pressure 128/80. He takes a GH peptide before bed.

Reading it through:

1. Against the age table, 25 ms is a little below the middle for 35 to 44 and inside the normal spread. Not abnormal on its own.
2. Has it dropped? It has been flat for months, so there's no recent fall to explain. That points to his baseline, not a new problem.
3. Resting heart rate of 67 is on the high side for a trained man and, by itself, explains a lot of the low HRV. Lower resting heart rate is the lever.
4. Haematocrit 0.50 and climbing is worth acting on whatever the HRV says: check for sleep apnoea, check hydration, review injection frequency and dose.
5. No cardio is the biggest missed opportunity. Aerobic training is the best-evidenced way to raise HRV and lower resting heart rate.
6. The bedtime peptide is untested. The only way to know is to log two to three weeks with it, then two to three weeks without, changing nothing else.

One plausible outcome: a sleep study, two or three zone 2 sessions a week and a month off alcohol move his number up a few milliseconds over a few months. Another: it stays at 25, his resting heart rate and haematocrit come down, and 25 turns out to just be his number. Either outcome is fine.

Decision tree: does my low HRV matter?

Step 1: Is it a dip or your normal? Compare your 7-day average with your own 30-day range on the same device. A single low night means nothing. In an HRV-guided training study, the rule that worked was simple: if today's value fell below your 10-day average minus one standard deviation, or trended down two days running, train easy that day (Kiviniemi et al., 2007). In that 4-week study of 26 men, those guided by HRV improved their maximal running speed more than those on a fixed plan, though the difference in VO2peak gain was not significant.

Step 2: If it's a sustained drop over weeks, despite rest, look at what changed: a new compound or dose, a cut, a training block, more alcohol, worse sleep, a rising resting heart rate. Change one thing at a time. Hard, high-intensity training blocks nudged HRV down in a small study of 9 elite rowers (Plews et al., 2014), and a falling HRV isn't always bad: in some fit athletes it drops while fitness improves (Plews et al., 2013).

Step 3: If it has always been low and nothing changed, it's probably your baseline. Check the fixable contributors (resting heart rate, haematocrit, blood pressure, sleep apnoea, alcohol) and stop comparing screenshots.

Step 4: If low HRV comes with symptoms, meaning palpitations, an irregular pulse, chest pain, fainting or breathlessness, the watch is no longer the right tool. See a doctor and get an ECG. An irregular rhythm also makes wearable HRV unreliable, because the device can't tell an extra beat from real variability.

Does low HRV mean heart disease?

At the population level, low HRV does predict heart problems. In a meta-analysis of 21,988 people without known heart disease, those with the lowest SDNN had 35% higher risk of a first cardiovascular event than those with the highest (Hillebrand et al., 2013). In Framingham, each one-standard-deviation drop was linked to 47% higher risk (Tsuji et al., 1996). After a heart attack, SDNN under 50 ms meant 5.3 times the death rate of SDNN over 100 ms (Kleiger et al., 1987).

But all of those used hours of clinical ECG recording, not a wrist sensor, and they describe groups, not you. A man on TRT with an HRV of 25 is not being told he's at 35% higher risk. He's being told to check the things on this page.

What to test if your HRV stays low

These are sensible checks alongside low HRV, not proven HRV causes. The point is to find something you can fix.

How to raise your HRV

In rough order of evidence:

1. Aerobic training. A meta-analysis of 13 studies found exercise training raised the vagal component of HRV with a moderate effect size and lowered resting heart rate (Sandercock et al., 2005). Two or three zone 2 sessions a week is the obvious missing piece for most lifters.
2. Slow breathing. Across 223 studies, slow, deliberate breathing (well under the usual 12 to 20 breaths a minute) raised vagal HRV during practice, straight after a session, and over multi-week programmes (Laborde et al., 2022). Five to ten minutes before bed costs nothing.
3. Treat sleep apnoea if you have it. A meta-analysis of CPAP studies found improved autonomic balance, though the results depend on when HRV is measured (Guo et al., 2018).
4. Cut alcohol, especially in the evening (see the Pietilä data above).
5. Bring resting heart rate and haematocrit down using the guides linked above.
6. Sleep and consistency. Same bedtime, same wake time, last meal a few hours before bed. These are sensible and widely seen in wearable data, though we didn't find a clean trial to cite for each.

Magnesium is often recommended for HRV. We found no solid evidence that it raises HRV in people who aren't deficient.

Practical recommendations

• Stop comparing your HRV with other people's screenshots. Age, genetics and device decide most of the gap.
• Build a baseline: 30 days on one device, same sleep window, and look at the 7-day average.
• Log resting heart rate next to HRV. If resting heart rate is up, that's most of your answer.
• On TRT, check haematocrit, blood pressure and sleep apnoea before blaming testosterone.
• On a cut with T3, clen or stimulants, expect HRV to fall and resting heart rate to rise. That's the drugs, and it's a reason to keep doses sensible and cycles short.
• Starting a new compound or peptide? Change one thing at a time, so your HRV data can actually tell you something.
• Symptoms trump numbers. Palpitations, chest pain or fainting mean a doctor and an ECG.

Key takeaways

• Average resting RMSSD in healthy men falls from about 40 ms at 25 to 34 to about 23 ms at 45 to 54 and 20 ms at 55 to 64, with a wide normal spread.
• 25 ms is below average at 30, about average at 45, and above average at 55. None of those is abnormal on its own.
• Apple Watch reports SDNN, most other wearables report RMSSD; overnight readings run higher than daytime clinic data. Compare like with like.
• No trial shows TRT at normal doses lowers HRV. The one small study of untreated hypogonadal men found their HRV was already low.
• Supraphysiological steroids, thyroid hormone excess and fast heart rates are the clear HRV killers. Tren, clen and GH peptides have never been studied for HRV.
• On TRT, check resting heart rate, haematocrit, blood pressure, sleep apnoea and alcohol first.
• Aerobic training and slow breathing have the best evidence for raising HRV. Treating sleep apnoea may help too, though the CPAP data are mixed.

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