QUESTION FROM A READER: Why does my heart rate spike at the start of a run?

A lot of people who run with heart rate monitors often see their heart rate spike at the beginning of a run, only to subside after a mile or two. This kind of spike only happens if you didn’t warm up long enough.

  • If the body isn’t warmed up, there is little blood flow to the muscles (and therefore little oxygen).
  • For a short period of time, the muscles have to work anaerobically, increasing the heart rate.
  • The body rushes to shunt blood away from the organs and towards the muscles. This is a major stressor.
  • The spike in heart rate subsides when increased blood flow (and the oxygen that comes with it) allows the muscles to work aerobically.
  • Therefore, the spike itself is an indicator that your heart rate was inadequate.
  • It takes 12-15 minutes for the body to warm up properly.

Before starting a bout of exercise, our body’s internal machinery is largely inactive. The metabolism is working at a very low level, the big muscles are relatively quiet, and blood is moving largely within the core—cycling through the various organs, and back to the heart and lungs.

Muscles are fed by vast networks of capillaries—tiny blood vessels existing within the muscles themselves—which ensure that blood goes to and from every muscle cell. During rest, the majority of these capillaries are constricted. Very little blood goes in or out of the muscles.

This eases the demand on the heart during rest: constriction of the capillaries and peripheral blood vessels means that the overall volume of the cardiovascular system is greatly reduced. The heart doesn’t need to pump very hard to maintain blood pressure, which keeps the heart rate relatively low.

During exercise, muscles demand a huge volume of blood flow, and so the capillaries dilate to accommodate it. But the body isn’t designed in such a way that the capillaries can expand pre-emptively. They expand due to exercise itself. Asking the body is asked to exert itself from a cold start can be a major stressor: it has to drain blood from major organs abruptly and it has to shove them into muscles whose capillaries haven’t dilated yet—a process that can send the body into shock.

Because of this, a proper warm-up—a period of very low-intensity activity—is important for all exercise, but is critical for running: Every step we run, our legs have to break our fall. It takes a big use of the muscles to make this happen.

Without proper blood flow, the muscles are on their own. If the capillary networks haven’t yet expanded, very little blood is getting to the muscles for those first few minutes. This is a problem because blood carries oxygen. No blood, no oxygen. But even without oxygen, the muscles still need to find a way to perform the required activity. In this situation, the only way to accomplish this is by working anaerobically.

I’ve written before how anaerobic work is intricately tied to the stress response: when the body is under stress, it raises the heart rate and kicks up the functioning of the anaerobic system—which is able to provide energy at a massive rate—in order to deal with a presumed threat to its existence. The connection between stress, anaerobic activity, and a high heart rate runs deep: if any of the 3 increases, the other two will follow.

The observed spike in heart rate is a direct indicator of increased anaerobic activity.

It subsides after a mile or two is because it typically takes the aerobic system 12-15 minutes to activate completely. Blood finally pervades the muscles, bringing oxygen and allowing the aerobic muscle fibers to do their thing.

Heart rate drops to a manageable level once the aerobic system is in play—and to the degree that it comes into play.

Here’s the important part: A spike in heart rate doesn’t just tell us that our aerobic system wasn’t fully on yet. It also tells us that our warm-up was inadequate. The spike in anaerobic activity means that blood and oxygen was largely absent from the muscles. The body was forced to rush to bring blood to the muscles. Blood was hastily drained from the organs, and unceremoniously shoved through capillaries that hadn’t yet expanded to accommodate it.

That amounts to a lot of unnecessary stress.

The solution: warm-up for longer.

21 thoughts on “QUESTION FROM A READER: Why does my heart rate spike at the start of a run?”

    1. So the warm-up should be defined as a period where the heart rate slowly and steadily rises until it reaches a certain point. If you need to slowly move your limbs, and then walk, and then do something like jumping in place for a few times, and then move your limbs again, in order to NOT produce this spike, then that’s what your warm-up has to be like.


    1. Jherek:
      The specific person who asked the question had already tried that. Your response applies only to electrode-based heart rate monitors. The article topic applies to (optical) wrist and ear monitors as well (or any other sensor type you could dream up). This is because the article is talking about exercise phenomena that affect the physical rate of palpitations of the heart, rather than specifically what the sensor (whatever type it may be) is managing to pick up. The reason why the article starts with a mention of heart rate monitors is because it’s typically people who are wearing heart rate monitors that get to experience this physiological phenomenon through heart rate measurement in real time. If you took your pulse, you would be able to experience it as well.


  1. Two points (for me). 1) This only happens to me when it is cold outside, so I assume that plays a role as well. It doesn’t happen in the summer. 2) Even though my HR spikes to near my theoretical max heart rate, it doesn’t feel like my HR is high. I was shocked to discover that this wasn’t an issue with my heart rate monitor and that by measuring my pulse it was REAL. But if I don’t feel like I’m operating anaerobically, and it doesn’t seem to hurt my performance, is there any harm in just ignoring the spike for the first 8 minutes? (For me it never lasts longer than 8 minutes).


    1. Hi BWorkman,

      When it is cold outside, that is actually usually a hardware issue with the HRM. The HR conductivity is very different in the cold, so it basically goes awry and stays high until the HRM warms up from your body heat 10-15 minutes later. The specific issue I’m referring to is when your heart rate spikes 20-25 BPM and then slowly begins to subside over the next 10-15 minutes or so. More specifically, you see this the other way around: individuals start running at their MAF HR or higher, and then over the course of the next 10-15 minutes they get way faster at that same heart rate. But when this happens at a walk or very slow jog (that bespeaks a much lower heart rate) it’s usually a hardware problem.


  2. I find my heart rate spikes during my warm up. It only seems to happen on a morning run – maybe my day is my warm up and by the afternoon/evening everything is ready to go?? However, the spikes are exactly that, 110bpm to 158 and then down to 108 in the space of 30s. At first I thought it was the HRM so I got another and I use electrode gel and that shows similar spikes. I don’t feel like my heart rate is that high, I’m not breathless. It spiked 3 times during my warm up this morning between 04 and 0.6 miles. Is this normal and is the explanation the same? Thank you.


  3. Thanks for this. I noticed this effect (HR spiking) during my warm-ups, but it would subside in ~10min or so, like you’ve indicated. So I’ve been waiting until it lowered back down before I started my training workout in earnest, as I didn’t want the high HR to throw off my numbers and give me ‘false’ information about workout intensity and so forth. Now I a) know *why* it’s happening and, b) how to avoid it (warm-up even more slowly than I’ve been doing). Perfect, mahalo! 🙂


    1. Hi

      Did the longer easier warm ups work for you?

      I’m experiencing the same 180bmp on warm up but I feel fine my heartrate, breathing and pace are all fine.

      7-8 mins in its back to normal for the session.



  4. I have noticed that about 50% of the time my heart rate spikes to 170-180 for about 5 minutes and then settles at 100-110 bpm. I am not a new runner, I have run 200 marathons but am 70 years old. I guess that I should ignore this spike in heart rate because it settles down soon after running.


  5. Hi John (and Joshua),

    What I’ve seen is that sometimes the “spike” is due to the electrodes of the heart rate monitor itself taking a while to warm up. So sometimes it’s a phantom measurement. But I’ve noticed that even in very cold weather, this spike rarely lasts beyond the first 10 minutes, which is well within the timeframe for a proper warm-up. By the time you start your workout, the heart rate monitor should be warmed up and ready to go.


  6. Since I wrote to you back in April, I purchased a Garmin Heart Rate Monitor strap to use with my Forerunner 235. Since I have been running wearing the strap, my heart rate when running is normal. My heart rate does not peak during the start of the run, it just increases normally at the start. I now wear the strap for all runs because I can’t trust the optical heart rate detected by the Forerunner to be correct.


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  8. Thank you!
    I have done a treadmill test at the physiology department and they only found a healthy individual!
    The spike comes occasionally and I feel that I’m out of energy. Then, after about 2k, I’m fit as a fiddle! Even when the start is slightly downhill, I sometimes experience this phenomenon. It have’nt happened when racing, though. Maybe the adrenaline changes the physiology? I have done 90 k with 1000 m ascent whithout a problem!
    Embarrisingly, I am a surgeon, and I should have figured this out by myself, but, when it all comes around, I am only an athlete like anybody else….


    1. Hi Magnus,

      Thanks for dropping in!

      Really interesting points.

      First off let me say these kinds of phenomena (heart rate spiking, etc.) are multifactor, turbulent, and underresearched, meaning that there’s not much data or conclusions either way, so I am speculating here:

      In regards to this happening when you feel out of energy: I read a paper at some point discussing how the supposed initial evolutionary cellular function of cortisol was to regulate glucose production. Although this is supported by new research that shows the role of cortisol in gluconeogenesis, (for example) my point is that cortisol is not fundamentally a stress hormone (although it is that, of course), but that instead it is a energy metabolism hormone. So if the body needs energy, it is going to first try to get it from glucose, which is metabolically much more liquid than fat, and it’s going to use a stress hormone to do that, which will necessarily trigger the many biological effects of a stress hormone, including an increase in heart rate. Of course it also makes sense that the the heart rate would go up for straightforward energy and oxygen supply reasons, but I make the energy metabolism point as (1) it is rarely made, and (2) when you are out of energy but not hypotensive, it makes sense that an increase in heart rate would be a second order effect, resulting from the intended first order effect of increasing glucose availability. (Of course, probably many other mechanisms have some role to play here.)

      In regards to the adrenaline: I would suspect that the body’s physiological preparation for competition, “gearing up” includes among other things a preemptive adrenaline response that together with other activated mechanisms substantially reproduces the effects of a warmup.

      Just spitballing, but I’d say that the effects that “gearing up” is more likely to reproduce are those related to nervous system readiness, organ and muscle irrigation, and fuel metabolism, while those that it’s less likely to reproduce are those related to joint stimulation and readiness as well as fine-tuning neuromuscular coordination, which seem more likely to be activated by actually getting the body in motion.



  9. Thanks Ivan. Very useful article and helps me understand why this sometimes happens to me. I noticed it only recently when I decided to move from from just the wrist monitor to a chest strap (based on some recent readings about wrist monitor inconsistencies). I am faithfully lazy about warm-ups, so your guidance makes sense, and it’s times to mend my ways.

    Btw, after multiple knee surgeries across the years, an orthopedic surgeon recommended NSAID a half-hour before running. I only remember to take one occasionally (again with the sloppy warm-up protocols), but based on your explanation, I am suspecting this may contribute to the problem with may capillaries told to constrict by the NSAID only for the body to then say…just kidding, I’m about to run!?!

    Thanks again for the insight.


    1. Greg,

      Thanks for commenting! I’d say that’s a pretty fair conclusion to make given what you know.

      Was the NSAID recommended for inflammation/pain? (just curious). If one of the issues is vasoconstriction then you may want to try nose breathing particularly during the warmup as it helps produce nitric oxide, a powerful vasodilator. And so it can help you stabilize the warm up a little bit better (if vasoconstriction is indeed an issue).

      On a final note, even though I warm up very extensively myself, and an extensive warmup has all sorts of benefits, I DON’T think a heart rate spike is really a huge problem, except for people that may be really oversensitive to stress or fragile (think overtrained athletes, people coming just out of major organ surgery, etc.).

      The article mostly is to point out what may be happening in the body and so to help make potential training modifications that may be deemed necessary (or not).



      1. Thanks again. Yes NSAID recommendation was for inflammation. At the time (7ish years ago), I had a medial meniscus tear in my knee which eventually led to partial knee replacement. The replacement has worked extremely well and I no longer face a chronic inflammatory issue.

        The nose breathing tip is great, and I also saw the 4-count breathing post. Very useful! (and ironic that such a fundamental act as breathing correctly gets so little attention in running literature). Thanks Ivan.


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