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High Heart Rate & Black Spots When Running: What It Means

Black spots or losing your coordination while running are your body telling you it isn't getting what it needs in that moment. Pair that with a heart rate well above what's expected for your age, and a running ability that's suddenly gone backwards, and that combination is worth a prompt doctor's visit — not something to train through.

Is Your Heart Rate Reading Actually Right?

Before anything else, it's worth checking the number itself. The standard estimate for maximum heart rate is 220 minus your age — a rough guide, not gospel, so get a more accurate max heart rate estimate if you want a sharper number. For a 52-year-old, that rough estimate lands around 168 beats per minute (bpm).

Nancy's reading of 190 sits around 22 beats above that. That gap cuts two ways, and both are worth taking seriously.

One possibility: the reading itself is inflated. Treadmill grip sensors are notoriously less reliable than a chest strap — they pick up grip pressure and motion as much as your actual pulse. The other possibility: the number is real, and a heart rate that far above your estimated max is worth a doctor's attention in its own right.

Here's the sensible first step, before drawing conclusions either way: repeat a run wearing a chest-strap monitor instead of relying on the treadmill's built-in sensor. It costs you nothing, and it rules out the simplest explanation first.

Black Spots and Losing Coordination: When This Is a Red Flag

Let's be direct about this one. Graying or spotted vision, dizziness, and losing your coordination or balance during exercise are not routine fatigue — they're near-fainting symptoms, and they're treated as a genuine warning sign. That's especially true when they're paired with a heart rate that's unusually high for the effort, exactly as Nancy describes.

This isn't an emergency-room-tonight situation. But it is a see-someone-soon, not see-someone-someday situation.

One thing matters more than almost anything else here: how you describe it. Tell your doctor specifically that this happens during exercise — graying vision, losing coordination, mid-run — rather than describing it generally as "stamina problems." That detail is what changes whether a doctor takes it seriously, or shrugs it off the way Nancy's did.

I'm not a doctor, and none of this is a diagnosis — it's triage guidance, based on what these symptoms usually mean, not a read on what's actually going on in your body specifically.

Worth Checking Promptly vs. Not an Emergency

If your situation matches the right-hand column instead — no black spots, no dizziness, a heart rate that settles quickly — you're most likely looking at a training and pacing question rather than a medical one. See heart rate feels too high but effort matches? Here's the difference for that scenario specifically.

Why Might Your Stamina Have Suddenly Dropped?

Set the scary symptoms aside for a moment, because there's a second question buried in Nancy's letter that's easy to miss: a genuine regression, not a plateau. Two months ago, 5 miles at 11 minutes a mile. Now, struggling past 4. That's not slow progress — that's going backwards, after 18 months of steady gains.

A sudden drop like that, after a long stretch of consistent progress, usually points to something specific rather than an ordinary plateau. Two of the more common, easily checked causes are iron-deficiency anaemia and an underactive thyroid — both worth raising with a doctor directly.

There are other everyday culprits worth ruling out too: dehydration or heat load, if this coincides with warmer conditions; poor sleep; a recent illness or infection your body's still recovering from. And given Nancy is running Monday, Wednesday, Friday and lifting Tuesday, Thursday with no rest day built in, simple overtraining and under-recovery deserves a look as well — wondering if this is overtraining instead? covers that angle in more depth.

None of this is a self-diagnosis list. It's a starting point for the conversation with your doctor, not a substitute for having it.

What to Actually Ask Your Doctor For

This is the part the old answer to this question never actually gave: a concrete starting point. Here's what I'd raise with a general practitioner (GP, or family doctor) in Nancy's position.

A full blood count with iron studies checks for anaemia. A thyroid panel — specifically thyroid-stimulating hormone (TSH) — checks thyroid function. And given the exertional black spots and loss of coordination specifically, it's worth asking whether a referral for a cardiac work-up makes sense: an exercise stress test or an ambulatory electrocardiogram (ECG), sometimes called a Holter monitor, are the standard ways to see what your heart is actually doing during a run, rather than guessing from a treadmill's number.

Here's the detail that makes the difference: naming the exertional symptoms clearly — black spots, loss of coordination, specifically during exercise — is what gets a doctor to consider that cardiac work-up, rather than filing it under general stamina complaints the way Nancy's earlier visits did.

In the Meantime: Training Adjustments

While the medical side gets sorted, there's still a sensible way to train. None of this replaces the doctor's visit above — think of it as running comfortably in the meantime, not around the problem.

A run/walk approach is the place to start. Run at a pace where you can still hold a conversation — even if that means a gentle shuffle — and walk when you need to, rather than pushing through.

Where you can, run outdoors instead of on the treadmill. Outside, your pace adjusts naturally to how your body feels in the moment. A treadmill's belt doesn't care how you're feeling — it just keeps moving.
Taking up running at 50 and building to 5 miles is genuinely impressive — don't let a rough few weeks erase that. Get the reading checked, get the doctor's appointment booked with the right words attached to it, and keep your training gentle until you've got answers. For more on getting the most out of a heart rate monitor, see the full guide to heart rate training.

All the best,
Dominique

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