Garmin metrics spike after a marathon but new study says your heart is fine
Marathon running temporarily strains the heart, but that stress doesn’t seem to cause long-term damage. A new decade-long study published in JAMA Cardiology puts to rest a persistent fear among distance runners and smartwatch users alike.
A rare long-term look at runner heart health
This study followed 152 male recreational marathoners over a ten-year period, with cardiac imaging conducted at multiple points. All participants had completed at least four marathons over that time, and many trained consistently. Researchers looked closely at how the heart responded both right after racing and in the long run.
Ejection fraction measures how much blood the heart pumps out with each beat. For the left ventricle, normal values are between 50 and 70 percent. Right ventricular values tend to be a bit lower.
Immediately after a race, runners often showed lower right ventricular ejection fractions and spikes in troponin T levels. For years, those findings raised concerns about possible long-term heart scarring or dysfunction. But this new data tells a more reassuring story.
The heart appeared to recover within days, and follow-up imaging a decade later revealed no signs of cumulative harm. Ventricular function remained stable and within normal limits across the group.
Granted, if you look at the figures below, there was a slight drop in both left and right ventricular ejection fraction over the 10-year period. However, aging alone could easily account for this small decline. In fact, such minor reductions are expected in any aging population, even among non-athletes.
Heart Measure | When Measured | Result (Median and IQR) | Change Over Time |
|---|---|---|---|
Right Ventricular Ejection Fraction | Before race | 52.4% (50.0–55.1%) | — |
Immediately after | 47.6% (44.7–51.5%) | Dropped significantly | |
Day 3 after | 51.3% (50.4–53.0%) | Recovered | |
10 years later | 51.9% (49.6–54.5%) | No lasting damage | |
Left Ventricular Ejection Fraction | Baseline | 59.6% (55.6–64.5%) | — |
10 years later | 57.6% (54.1–61.6%) | Small drop, still normal | |
LV Filling Pressure (E/e′ ratio) | Baseline | 5.1 (4.3–6.1) | — |
10 years later | 5.4 (4.5–6.4) | Slight increase |
What this means for wearable users
Over the last few years, wearables have made it much easier to track every small change in heart rate, recovery time, or HRV after a race. But while data like this is useful, it can also lead to overinterpretation. Just because your Garmin or Whoop shows a spike in resting heart rate or a dip in recovery scores after a marathon – doesn’t mean damage has occurred.
This study makes it clear that some degree of cardiac stress is normal after long endurance events. Elevated metrics aren’t red flags on their own. They’re part of the body’s adaptation and recovery cycle. What matters more is the trajectory. Most runners bounce back within days, and this is echoed both in wearable metrics and in clinical imaging data.
The limits of what your watch can see
It’s also worth noting what wearables cannot detect. This study relied on advanced tools like cardiac MRI and echocardiography to assess actual heart function. Your wrist-based sensor won’t capture ventricular ejection fraction or subtle wall motion changes. So if a post-race spike in troponin or heart rate data shows up, it’s not the full picture. And according to this research, even those spikes may not be meaningful in the long run.
The findings should also help reframe how wearables are used. Rather than obsessing over each post-race anomaly, athletes could use these devices to monitor recovery trends. If recovery consistently stalls or baseline metrics remain abnormal for weeks, that’s when it might be time to dig deeper.
The bigger message
I’ve run a couple of marathons in the past year, but in the back of my mind were stories about how this could be doing more harm than good to my heart. Spikes in heart rate, warnings about troponin levels, and debates over long-term damage were enough to make anyone question whether repeated endurance racing might leave a mark.
This new study is one of the clearest pieces of evidence yet that recreational marathon running doesn’t gradually wear out the heart. It may briefly strain it, but that’s a very different thing.
That’s good news for runners who train hard, race regularly and track their vitals obsessively. Short-term shifts in data are part of the process, not signs of injury. If anything, this study supports the idea that the heart adapts to endurance stress rather than breaking down from it.
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