Why Running Feels So Hard at First, and Why Your Heart Rate Soars
Asier G. Morato
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7
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Cover image generated with AI — © Chubby Studio S.L.
KEY TAKEAWAY
A high heart rate on early runs is normal for most healthy beginners: even a slow jog is vigorous exercise for a body that has not adapted to running yet. Slow down until you can talk in full sentences, walk when you need to, and expect the same pace to feel easier within a few weeks. Chest pain, dizziness or an irregular heartbeat are reasons to see a doctor.
Running feels hard at the start because it genuinely is hard for your body at the start. Even a slow jog is a big step up from walking, and a heart that is not used to it answers with a high rate: 160, 170, sometimes more, on runs you meant to be easy. For most healthy beginners that is normal and temporary, and the fix is to slow down more than feels reasonable, not to push through.
If you just finished a run feeling like your chest was about to take off, none of this means you are not built for running. It means your body has not caught up with what you are asking of it yet.
Why is my heart rate so high when I run, even slowly?
Because your slowest jog is still vigorous exercise for a body that has not adapted to running. Running lifts your whole body weight off the ground with every stride, so there is no truly gentle version of it the way there is with walking or easy cycling. Until your heart, blood and muscles adapt, the only way to meet that demand is to beat faster.
Three things stack up in the first weeks. Your heart pushes out less blood per beat than it will after some training, so it needs more beats for the same job. Your muscles are less practised at taking oxygen out of the blood. And the pace that feels slow is almost always faster than the effort you intended, because nobody new to running wants to jog at something close to a walk.
On top of that sits everything that raises heart rate on any day: heat, a stressful afternoon, a short night, the coffee you had an hour before. The same run really does cost more on some days than on others, which is why the same run can cost you more on a bad day. A beginner has less margin to absorb it, so the number jumps further.
How high is too high for a beginner runner?
For a healthy adult with no symptoms, a high number on its own is usually not dangerous. The American Heart Association puts moderate exercise at about 50 to 70% of maximum heart rate and vigorous exercise at about 70 to 85%, and suggests beginners aim for the lower end and build up. Sitting above that band on a run meant to be easy is a pacing signal, not an alarm.
Put numbers on it. For a 40-year-old, the AHA chart estimates a maximum of 180 beats per minute, which makes 85% about 153. A new runner of that age jogging along at 165 to 175 is well above the vigorous band on what they think is an easy run. That is the most common story behind a heart rate that looks too high: the effort is too high, and the slow pace is only disguising it.
Keep in mind that the chart is built on 220 minus age, and the AHA itself calls its figures averages. Your real maximum can sit well above or below the estimate, which is why zones drawn from an age formula can be a full zone off. If your true maximum is higher than the formula says, a reading of 170 is less extreme than it looks.
When is a high heart rate while running not normal?
When it comes with symptoms. Chest pain or pressure, feeling faint or dizzy, a heartbeat that feels irregular or keeps racing long after you stop, or breathlessness far out of proportion to what you did are reasons to stop and get checked by a doctor before running again. A number on a screen, without any of those, usually is not.
The same goes if you have a known heart condition or take medication that affects heart rate. In that case the AHA advises asking your health care professional what your heart rate should be, and that answer outranks anything a chart, a watch or an article can give you.
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How long until running stops feeling this hard?
Usually a few weeks of regular running, not a few months. The earliest changes happen in your blood and your heart: training expands your blood volume, which lets your heart fill more and push out more per beat, so it can do the same work at a lower rate. Most beginners notice the same slow pace feeling easier, and reading lower, well before they get any faster.
The physiology moves quickly. In a 1991 review, Convertino described plasma volume expansion as accounting for nearly all of the early rise in blood volume in the first two to four weeks of endurance training, and linked that larger volume to a bigger stroke volume and lower heart rates during exercise. In a small study by Murias and colleagues, men training three times a week already had a higher VO2 max after three weeks, with further gains by week twelve. That study used a bike rather than running, and only 16 people, so read it as a sense of pace rather than a promise.
What changes more slowly is everything that is not cardiovascular. Tendons, bones and the muscles around your shins and ankles adapt over weeks and months. Your heart and lungs will tell you that you are ready for more before your legs actually are, and that gap is where most running injuries start. It is worth remembering the week running suddenly starts to feel good.
How do you run slowly enough?
Slow down until you can speak in full sentences, and if that means walking, walk. The talk test is not a beginner's gimmick: a review in Current Opinion in Cardiology found that comfortable speech is generally possible below the ventilatory or lactate threshold and not above it, and called the test valid and reliable across walking, jogging and cycling.
For the first weeks, that looks like this. Run by breath, not by pace. If you cannot say a full sentence, slow to a walk until you can, then jog again. Expect your easy jog to be barely faster than a brisk walk, and read nothing into that: it is where almost everyone starts. Walking breaks are a legitimate way to train, not a sign you failed the run.
Heart rate zones help once they are right, and the easy zone is where you will spend most of your time. Zone 2 is the easy aerobic work that makes you faster over time, but for a beginner it can mean alternating short jogs with walking for a while. That is fine. The talk test and the zone should roughly agree, and when they do not, trust your breathing first and then check how your zones were set.
What should you look at on your watch in the first weeks?
The trend, not the peak. One run with a scary maximum tells you almost nothing. The same loop at a similar pace, with a heart rate that sits a few beats lower week after week, is the clearest sign that your body is adapting, and it usually shows up before your pace changes at all.
A few habits make that trend readable. Run the same route for your easy sessions so the terrain is not changing the number. Look at the average heart rate for the steady part of the run rather than the maximum. Ignore the first few minutes: heart rate takes a while to settle, and an optical sensor on your wrist can briefly lock onto your step rhythm instead of your pulse, which shows up as a sudden flat line sitting suspiciously close to your cadence.
Your resting heart rate is worth a glance too. As fitness builds, many people see it drift down over weeks, and a sudden rise is often the first hint that you did too much, slept badly or are coming down with something. We wrote about what a rising resting heart rate is warning you about.
How FitWoody reads your first runs
FitWoody works from the data your Apple Watch already records. It analyses each run against your own cardiac load rather than a generic pace, so a slow run on a hot day or after a short night shows up as the harder session it was. You can set your own heart rate zones instead of relying on an age formula, and your training load sits next to your sleep and recovery baselines, so a week where running felt awful can be read against how rested you actually were. For outdoor runs, Flyover replays the route with your heart rate moving along it.
Where to start this week
If running feels brutal and your watch agrees, you are not doing it wrong. Slow down until you can talk, let walking be part of the run, and keep one easy loop so you can see the change. The number comes down because your body changes, and it changes faster than it feels like it will.
Frequently asked questions
Is a heart rate of 170 too high for a beginner runner?
For a healthy adult with no symptoms it is usually not dangerous, but it is probably harder than the easy run you intended. The American Heart Association puts vigorous exercise at 70 to 85% of maximum heart rate, which for a 40-year-old on its chart tops out around 153. Slow down until you can talk in full sentences. Chest pain, dizziness or an irregular heartbeat are reasons to stop and see a doctor.
Should I walk when my heart rate gets too high while running?
Yes. Walking until your breathing settles and then jogging again is a legitimate way to build running fitness, not a failed run. For the first weeks, running by breath, meaning you can still speak in full sentences, is a more reliable guide than pace, and often more reliable than zones set from an age formula.
How long does it take for my running heart rate to come down?
Usually weeks rather than months of regular running. Training expands blood volume, mostly plasma, within the first two to four weeks, which lets the heart pump more per beat and beat less for the same effort. The clearest sign is the same route at a similar pace showing a lower average heart rate over several weeks.