Is my Polar RS800cx a boon or a curse?

My Polar RS800cx heart rate monitor has created chaos. I purchased it last summer with the hope that measuring heart rate variability would help me answer the most challenging question facing any runner trying to maximize performance with limited training time: the question of finding the optimum balance between training load and recovery. Almost a year later, I do not know whether has been a great benefit to my health and wellbeing, or a curse that has blighted my running.

There is little doubt that the beneficial effects of training depend as much on the quality of recovery as on the quality of the training itself. One answer is to spend a lot of time sleeping. This is the answer adopted by many African athletes and also individuals such as Paul Radcliffe. Unfortunaltey, for many of us with commitments to jobs and family, this simple solution is not practical. So in an attempt to maintain the balance between stress and recovery we try to find some measurement that will allow us to push our bodies far enough to reap the benefits of training, but warn us when we are in danger of pushing beyond the point where additional training becomes counter-productive.

One of the most promising is measurement of the balance between the two arms of the autonomic nervous system. This system has two opposing components: the sympathetic component which exerts its effects via adrenaline, and mediates the response to stress; and the parasympathetic component which acts through the messenger molecule, acetylcholine, that mediates relaxation and recovery. Fortunately, we can monitor the balance between sympathetic and parasympathetic activity relatively easily by measuring the beat-by-beat fluctuations in heart rate. This requires a heat rate monitor with the capacity to measure and record R-R intervals – the intervals between successive R waves (in the ECG) generated by successive heart beats. High frequency beat-to beat fluctuations (at frequencies around respiratory frequency or higher) reflect parasympathetic activity. Lower frequency fluctuations represent sympathetic activity.

The principle is simple: by measuring heart rate variability (HRV) during a period of a few minutes under consistent circumstances each day (eg after getting up in the morning) we can determine whether the amount of high frequency fluctuation indicates an adequate level of recovery and hence indicates that we have recovered sufficiently to benefit from a hard training session that day. Not only is the principle is very simple, but the practice also appears beguilingly simple in an era when electronic devices that existed only in the dream-world of science fiction during my childhood, can now be purchased for a sum of money not much beyond what my teenage son would happily spend on tickets for a rock concert. Both Polar and Suunto produce heart rate monitors that will provide the required R-R data, which can be readily uploaded to a computer for analysis, while other devices, such as Ithlete, can be plugged into an ipod or an iphone to produce an apparently easily interpreted on-screen message.

The scientific evidence

However, despite the simplicity and accessibility of the data, there is remarkably little good scientific evidence that daily monitoring of the autonomic nervous system leads to optimal training. In a promising small study [1], Kiviniemi and colleagues from Oulu in Finland compared a group 9 runners randomly assigned to a 4 week training program adjusted according to daily measurement of HRV, with 9 runners assigned to a conventional fixed training plan comprising four high intensity and two low intensity sessions each week. The group whose training load was reduced on days when the HRV measurement indicated inadequate recovery showed a significant increase in VO2 max whereas the group following the fixed schedule did not. Furthermore the group whose training was adjusted according to HRV showed a significantly greater increase in maximum running velocity on a treadmill test. This study supports the hypothesis that adjusting training according to level of parasympathetic activity leads to better performance.

A much more detailed study of 8 runners preparing for a marathon [2] by Manzi and colleagues from Rome, also suggests that HRV can be informative, but leads to a more complex conclusion. I will review Manzi’s study in greater detail in my next post, but the main conclusion is that relatively greater ratio of low frequency variability to high frequency variability, indicating relatively more active sympathetic nervous system activity, predicts better marathon performance. Overall, the evidence suggests that HRV can be informative, but the interpretation of the data is complex.

My experience

Meanwhile, my personal experience with my Polar RS800cx has been even more perplexing. In February, I posted an R-R recording that appeared to indicate that I have atrial fibrillation (AF).  I have subsequently posted several discussions of the paradoxical evidence that endurance training is associated with increased risk of AF. John Bedson, who runs a support group for people with AF and has a wealth of information about the condition, is adamant that my trace shows AF. I am less sure, but I am nonetheless taking the evidence seriously. I have in fact been investigated fairly thoroughly by a cardiologist; so far without any clear evidence of heart abnormality emerging. An echocardiogram revealed a normal heart structure and ECG revealed only the mild hypertrophy expected in an endurance athlete.

Unfortunately, the interpretation of the evidence from my Polar is confounded by clear evidence that the device is unreliable in a number of respects. Despite appearing to function well on many occasions, there are times when the trace makes no sense at all (for example showing quite long periods of unbelievably low heart rate); sometimes the data is not recorded; sometimes pressing the various buttons does not achieve the intended effect, sometimes the transmission of data from the device to my computer does not work properly. I had sent it back to Polar (UK) a few months after I purchased it. They kept it for five weeks and after they returned it, I found that they had corrected a fault in the foot-pod, but did not appear to have done anything to deal with several of the other inconsistencies.

One of my reasons for deciding to purchase the RS800cx was my belief that Polar produce good quality equipment. Subsequent to my unfortunate experiences, several people have shared anecdotes about erratic behavior of their Polar HRM’s but in most instances, the company were prepared to replace defective equipment. I accept that the RS800cx is a sophisticated device and it is perhaps not surprising that sometimes things go wrong. However, it seems to me that a company that produces such products for the market at cost that is modest but not entirely trivial, should be prepared to offer good service. I am about to send my RS800cx back to Polar once again, in the hope that they can either rectify the problem or replace the device.

So at present I face a quandary.  If I really do have AF, I owe substantial gratitude to Polar for allowing me to discover it. AF occurring without overt symptoms is potentially quite dangerous, especially as AF begets more AF. It is important to minimize the duration of episodes of AF. On the other hand, I believe that complete cessation of exercise would be even more harmful to my long term health. Thus, learning how to adjust my level of exercise to minimize AF, if indeed I suffer from AF, is crucial. A reliable HRM offers me the best prospect of being able to continue to run in reasonable safety. However, a monitor that produces unreliable data merely generates uncertainty and anxiety.


[1] Antti Kiviniemi, Arto Hautala, hannu Kinnunen & Mikko Tulppo (2007) Endurance training guided individually by daily heart rate variability measurements. Eur J Appl Physiol. 101(6):743-751.

[2] Vincenzo Manzi, Carlo Castagna, Elvira Padua, Mauro Lombardo, Stefano D’Ottavio, Michele Massaro, Maurizio Volterrani, and Ferdinando Iellamo (2009) Dose-response relationship of autonomic nervous system responses to individualized training impulse in marathon runners Am J Physiol Heart Circ Physiol 296: H1733–H1740.


11 Responses to “Is my Polar RS800cx a boon or a curse?”

  1. George Says:


    I looked at your image on Looks like afib to me. I wrote most of that John referred you to. I have lone afib and got there by way of chronic fitness. I’ve got several Polar S810’s – the predecessor to your model. While the transmitter can loose contact and either drop or produce artifact, I find the device remarkably reliable – having made 1,000’s of recordings. Your data clearly looks like afib. A 30 day recording event monitor (ECG) would tell for sure (assuming at least that frequency of afib). Newer models will look for arrhythmia and notify you to transmit the data for analysis.

    “I believe that complete cessation of exercise would be even more harmful to my long term health.” Here is my take on this – my conclusions: The primary benefit of exercise is insulin sensitivity. Exercise is one way to achieve this. Diet is another. Within the exercise realm, strength training and interval training are much more efficient than endurance training for this purpose. I’ve personally dropped endurance training & emphasized diet, strength and interval training.

    Richard Bernstein is a Type 1 diabetic – diagnosed at age 12 in the 1940’s. He became an engineer and in his 30’s his health deteriorated, as did that of most Type 1’s of his generation. He figured out very tight blood sugar control using some of the initial glucometers. He was frustrated in publishing on this. So at age 45, went to medical school and became a doctor. He’s been treating diabetics since the early ’80s. His own average blood sugar is 83 mg/dl (4.6 mmol/l). His A1C result is 4.5%. He published his blood lipid results and they are outstanding for anyone from the first world. The fact that he’s been a Type 1 for ~65 years is even more amazing. He says that his results are not unusual for his patients who are compliant with his guidelines. He also notes that interval exercise is 17x more efficient at clearing glucose from the body. The latest edition of his book was published in ’07 and at that time he was still actively seeing patients at age ~77. My take is that even most “normals” are getting complications of diabetes as they age – just on a slower track. Bernstein’s path is a way to avoid this.

    Taking a cue from Dr. Bernstein, I got an accurate (many aren’t) home glucometer (Bayer Ascencia Countour) (I’m not a diabetic). and learned to eat so that my fasting glucose is around 75 mg/dl. I tried not to spike my blood sugar to higher than 100 mg/dl 45 minutes after meals (generally the maximum). I have moderated training to less than 45 minutes – mostly core and strength training with a few short (<20 min) interval sessions a week. I'm still active – rock climbing & skiing, but do not concentrate on endurance activities. Results – resting HR in the 50's, BP 98/56.

    Afib is kept in remission with K+, Mg++ and taurine supplements. Mg++ being the most important. Magnesium glycinate is the most bioavailable. The idea is to start with a low dose and titrate up to bowel tolerance & back of slightly. Potassium in food and supps should total 4.7 grams/day. Most find that the K gluconate powder is tolerated most easily. Personally I take something greater than 2 grams/day elemental magnesium in the forms of glycinate, citrate, chloride and bicarbonate. Potassium is around 2 grams a day (elemental), half from chloride and half from citrate. Taurine is 4 grams/day. Spread all of the above out and don't take the potassium with the mag as it will interfere with absorption. This mix has kept afib to about 10 one-hour episodes in 5.5 years. Most of those episodes can be correlated with inadequate magnesium intake or the aftermath of all day heavy exercise, or both.


    • canute1 Says:

      Dear George,
      Thank you for that advice. I agree the trace does look remarkably like AF, and there is also other circumstantial evidence supporting a diagnosis of AF. On the other hand, I have never been able to detect AF by manual palpation of my pulse so I would be re-assured if I could trust my RS800cx.

      I am interested that you still do interval sessions , and would be grateful if you could provide a little more detail about what you do in these sessions

  2. George Says:


    So your comment, “I have never been able to detect AF by manual palpation of my pulse” brought back memories of a few unusual heart rate strips. I went back through my files and there are a couple that I know are not afib but look a lot like yours. Unfortunately, I don’t remember exactly what I was doing to cause the artifact. I do know they aren’t afib as I note those specifically. A lot of artifact in the data is unusual, but not something I particularly make a record of. Looking at yours more closely – I not have my doubts that yours is afib. If you care to email me, we can trade hrm files.

    I can say that there is nothing wrong with my monitor. Had many perfect readings before & after. It was something about the transmitter wetting, how loose it was, what I was doing with my arms or the like that caused the artifact.


  3. Ewen Says:

    On the idea of using the 800cx as a training tool, it’s a shame that it’s possibly unreliable. I’d be going for a money-back offer and then buy the Suunto.

    The study by Kiviniemi looks promising. Correct me if I’m wrong, but wasn’t that the one that was “sponsored” by Polar? I wouldn’t be calling 4 high intensity and 2 low intensity training sessions per week “conventional.” 3 high intensity and 11 low intensity would be conventional for an elite distance athlete. Maybe 2 high intensity and 4 low intensity is conventional for a distance running amateur.

  4. canute1 Says:


    Thanks for your comments. The participants in the Kiviniemi study were healthy recreational male runners recruited from a local sports club. Low-intensity exercise was 40 min jogging at 65% of maximal HR. High-intensity exercise was 30 min of ‘tempo’ running at 85% of maximal HR between 5-min warm-up and cool-down at 65% of maximal HR.
    The study was funded by the Finnish Ministry of Education. However it should be noted that one of the four authors, Hannu Kinunnen works for Polar.

    In next months edition of Med Sci Sports Exerc (42(7):1355-63, July 2010) Kivniemi and colleagues report a study of two different schedules of HRV guided training compared with ‘standard’ training comprising two or more sessions at moderate and three or more sessions at vigorous intensity weekly in moderately active men and women. There were no group differences in gains in VO2 max, but the men in the HRV guided groups showed greater improvement in maximum load during a cycle ergometer test than the men in the ‘standard’ training group. In the females there were no group differences in maximum load, but those females in the more conservative HRV guided group achieved the same gain as the ‘standard ‘ group with less exercise.

    Overall, Kiviniemi and colleagues are assembling evidence suggesting moderate advantages of HRV guided training.

  5. Ewen Says:

    Thanks Canute. 4 x 30mins at 85% MHR is a lot of volume at high intensity (with not enough easy running for recovery). That’s 2 hours, so more than a 1/2 marathon’s worth of time at not much less than HM race effort weekly. I’m just saying that if that group did true conventional training they might have performed as well as the HRV guided group. From a results perspective HRV training doesn’t seem as good as traditional training. How many elite groups/runners use HRV to guide their training?

  6. canute1 Says:

    Ewen, Thanks. I agree that the standard program does not have enough low intensity sessions. In the more recent study (published in next month’s Med Sci Sport Exerc.) the conservative HRV guide strategy resulted fewer tempo sessions than standard, while the less conservative HRV guided method resulted in even more tempo sessions than the standard regime. The men following the HRV guided approach increased max load in the ergometer test more than those following standard training. Thus, at least in the men, HRV guidance appeared to allow them to train even harder than standard and to show benefit (over the short term) from this.
    However I agree with your skepticism – mainly because I think that Manza’s study suggests different conclusions. So at this stage, I would not recommend heavy reliance on HRV guidance for routine use. I will discuss these issues in more detail in futre posts.

  7. Simon Says:

    Hi Canute,
    First of all, sorry to hear that your marathon preparation has been hit by episodes of AF, and I hope that this can be brought under control.
    Secondly, I would like to make sure you are aware of the study by Martin Buchheit et al in Eur J Physiol Dec 2009, that also monitored daily within-individual parasympathetic HRV, both in the morning and post exercise. This was not used to guide training intensity, but rather passive monitoring found an association between improvements in 10k race performance and an increasing trend of parasympathetic HRV, especially that measured first thing in the morning.
    Thirdly, with respect to low frequency (LF) HRV, the interpretation is widely disputed, and it is currently not considered by many to be a valid or consistent indicator of cardiac sympathetic tone, but more likely an indication of baroreflex gain.
    Finally, the conclusions of Manzi may parallel those of Iellamo in 2002, who found that world class rowers progressed from increasing parasympathetic dominance to sympathetic dominance with increasing intensity of training over several months pre-competition. I think it likely that increases in parasympathetic HRV signal or even precede improvements in base aerobic conditioning, whereas high intensity training alters the autonomic balance back in a more sympathetic direction.

  8. canute1 Says:

    Thanks for your comment. I agree that the interpretation of the Manzi study of marathon runners (like the earlier study of rowers by Iellamo and colleagues from the same team in Rome) is that more intense training produces sympathetic predominance. Manzi reported that sympathetic predominance in the final assessment before the race was a good predictor of performance. The simplest interpretation is that those who are fit enough to train most intensely a few weeks before the race perform best.
    I think that the issue of whether or not HF HRV provides a more useful measure of recovery during routine training than a simple record of resting HR is still an open question, though the Kiviniemi data does provide at least some support for the value of measuring HF HRV. I will review the evidence in greater detail in a blog posting in the near future.

    Meanwhile I am considering ways of obtaining a real-time read-out of R-R intervals on a portable device that could be easily inspected while running. As I imagine it, Ithlete detects the wireless signal from a Polar transmitter and generates a voltage spike corresponding to each R wave, in a form suitable for input to an iPod. I remember you once told me your app computes RMSSD over a one minute time interval and displays a number related to this on the iPod screen. I would imagine it would be possible to write an app that would simply display a running record of R-R intervals on the screen. Alternitvely, it might be even more practical to generate a click for each R wave and send this to the earpiece jack, though I am not keen on the idea of running with an earpiece. I would be interested in your comments on the feasibility of this. I do not own an iPod, but if this were possible, I would be tempted to buy one, together with an Ithlete.

  9. Simon Says:

    Hi Canute
    Yes, the ithlete technology is based on the detection of coded R waves transmitted from analogue HR straps, with subsequent digitisation of RR intervals to an accuracy of 1ms. We are shortly to release an exercise HRM based on this same technology and would be willing to create a version for you to assist with AF onset detection during your runs. Please email me personally or via if this is of interest.

  10. Aaron Says:

    I use a Polar FT7 and can confirm that cell towers will cause a significant misread of your heart rate. There’s a particular route that has me pass within 50 feet of one soon after starting. During that time my heart rate will jump from about 100 bpm to 160+ and stay that way until I shut if off and get clear of the interference.

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