After yesterdays’ post on HRV guided-training, in which I discussed the two studies by Kiviniemi and colleagues [1,2], I realized that what I had written might give the impression that I undervalue the findings of those studies. Although I do not consider that those studies provide convincing evidence about the practical value of HRV-guided training, I do consider that they provide some very thought-provoking findings. To me the crucial point in both studies is that they demonstrate that for recreational athletes, doing more than three intense sessions per week is likely to result in over-reaching.
In the first study, the control group performed four high intensity sessions per week while in the second study the control group performed an average of 3.3 high intensity sessions per week These studies provide clear scientific confirmation of a fact that many athletes and coaches have discovered through experience: doing more than three high intensity sessions per week is counterproductive. In the case of frequent intense sessions, more pain does not usually produce more gain.
A further conclusion that can be drawn from these studies is that even for recreational runners there is a fairly narrow gap between the training load that is required for worthwhile improvement in performance, and the training load that results in over-reaching. Because most recreational athletes do not have an experienced coach to steer them between Scylla and Charybdis (the mythical sea monsters on opposing rocky shores, threatening to wreck hopes from either side) each individual needs to work out a satisfactory way of judging for themselves how intensely to train.
What do we hear when we listen to the body.
One approach is simply to ‘listen to the body’; reduce intensity whenever the body complains; and rest whenever the level of fatigue becomes excessive. The problem with this approach is that it is very difficult to decide what level of fatigue indicates significant over-reaching. It is not uncommon to experience sluggishness during the early part of a training session and then fell lively later in the session. If we rest whenever we feel moderate fatigue we are unlikely to achieve our full potential.
Another approach is to include an easy week in the schedule every fourth or fifth week. In general, this can be a fairly successful strategy, and is included in many recommended training schedules. However, there is little evidence to guide an individual regarding to the adjustment in load that is best for him or her. Optimizing training for the individual requires knowledge abut the individual’s own response to training.
My own experience, particularly in the period following my episode of illness last summer, is that measurements of heart rate and heart rate variability do provide a useful guide in deciding whether feelings of fatigue indicate significant over-reaching. However, I am still undecided as to which measurements are most informative. Last August, I found that the decrease in the magnitude of the heart rate rise during an orthostatic test was the most reliable guide (as discussed in yesterday’s post). However, at that time I was suffering from parasympathetic over-reaching.
The studies by Kiviniemi and colleagues suggest that even the early phases of sympathetic overreaching are associated with diminished benefit from training. Therefore, I am still eager to explore the possibility that HRV might be a practical guide to adjusting training intensity. While I do not think the studies by Kiviniemi provide convincing evidence, I think the evidence that they do provide is encouraging.
In recent weeks I have focused on the role of my Polar RS800cx in alerting me to the possibility of atrial fibrillation. While this has been an interesting and perhaps important diversion, my primary purpose in obtaining a Heart Rate Monitor with the capacity to measure heart rate variability (HRV) had been to explore its utility for monitoring my training, and in particular, for the identification of over-reaching and overtraining. In this post, I will return to my original purpose, and address the question whether or not it has proven useful. But first of all, it is worth reviewing the published literature on the subject.
The most consistent body of evidence comes for studies that employ measurement of HRV at rest. Several different processes contribute to fluctuations in heart rate. One of the most important is the fluctuations known as respiratory sinus arrhythmia (RSA). Heart rate accelerates as you breath in and decelerates as you breath out. This fluctuation is a one of the main contributors to high frequency fluctuations in HR (frequency range 0.15 – 0.4 Hz). At rest, RSA is governed by the parasympathetic division of the autonomic nervous system. It serves to ensure that the flow of blood via the pulmonary artery from heart to the lungs in maximal when the lungs are full of air. You can easily appreciate this variation in heart rate by manual palpation of the pulse at your wrist as you breathe in and out slowly. The magnitude of this fluctuation provides a good measure of the activity of the parasympathetic nervous system, which has the overall role of regulating bodily processes concerned with rest and recovery. Hence, the magnitude of RSA at rest is a fairly good indicator of how well recovered you are from a heavy training session.
In general, heavy training causes a short term reduction in high frequency HRV but as recovery proceeds there tends to be a compensatory rebound reflecting increased fitness. If HRV is still reduced the morning after an intense training session, yet another intense session is likely to produce yet further reduction the following morning, but eventually there is a somewhat paradoxical switch from parasympathetic under-activity to parasympathetic over-activity – perhaps the body’s self-defense strategy in the face of persistent stress By this stage, parasympathetic over-reaching is on the way to becoming the seriously debilitating condition know as parasympathetic over-training, characterized by persistent fatigue, low mood and reduced performance.
In principle, monitoring high frequency HRV each morning can be used to determine whether or not you are sufficiently well recovered to undertake another heavy training session. The practicality of this was first demonstrated in a study by Kiviniemi and colleagues from Oulu in Finland . They used morning measurements of high frequency HRV to adjust the training of a group of male recreational athletes over a period of 4 weeks. They compared increases in fitness, assessed by measurement of VO2max and also maximal running speed during a graded maximal exercise test on a treadmill, in 9 young men who trained according to HRV guidance, with the increases in fitness in a matched group of men who undertook a fixed training schedule comprising 4 high intensity sessions, 2 low intensity session and one rest day per week.
In the HRV guided group, HRV was measured using a Polar s110 monitor, during 3 minutes of sitting followed by 5 minutes of standing at home each morning. Because parasympathetic effects in fit athletes can be saturated when sitting, HRV during the 5 minutes of standing was employed to guide training. The calculation was done automatically using Polar software, and included a quite elaborate procedure for removal of artifact. The full details of the schedule for adjusting training according to HRV were complex, but the crucial issue was that it high frequency HRV measurement was below a threshold level set at one standard deviation below the mean of the measurements in the preceding 10 days, low intensity training or rest was selected for that day.
To check on the reliability of the calculation of HRV, the data was subsequently examined in the laboratory using a more sophisticated procedure based on an 18th order autoregressive spectral model. One the 10 subjects was dropped from the study because the laboratory check did not agree with the automatic computation performed at home. In view of the frequency of artifacts in HRM data, this is perhaps not entirely surprising, though in my own experience, artifacts during resting or standing recordings are extremely rare if the belt has been properly moistened. Maybe there was some other malfunction, or perhaps the subject had an abnormality of heart rhythm. Whatever, the explanation, the fact that 1 in 10 subjects was dropped is an indication that automated measurement of HRV is not entirely free of technical hitches.
The outcome of the study was that the HRV guided group showed increase in both VO2max and also in maximum running speed in the treadmill test (from 15.5 to 16.4 Km/Hr). The comparison group who followed the standard training protocol also showed improvement, with maximum running speed in the test increasing from 15.1 to 15.7 Km/Hr. The increase in maximum running speed was significantly greater in the HRV guided group. The difference between groups in in increase in VO2 max was not statistically significant.
Thus, this study provides encouraging evidence of benefits of HRV guided training. However, before recommending that serious athletes should invest in a HRM with the capability of measuring HRV, several points should be noted. Most important was the fact that the standard training protocol included 4 intense sessions per week, in two back-to back pairs of sessions. Many coaches and athletes would regard back-to-back intense sessions as creating too great a risk of over-training. The intense session involved warm-up followed by 30 minute tempo run at 85% HRmax, which I would regard as only moderately high intensity. Nonetheless, the fact that in the HRV guide group the average number intense sessions was only three per week indicate that that appreciable over-reaching occurred at least once per week on average, confirming what many sensible coaches and athletes know: back-to-back intense sessions are risky. This would be expected to impede the development of the benefits of training. Furthermore, it is probable that at least some of the standard group were in a state of over-reaching which might have impaired performance on the test day. In the example provided in the manuscript, illustrating the training of one of the individuals in the standard training group, the individual did show evidence of impaired HRV on the test day. Finally, in view of the non-trivial the cost of a HRM capable of measuring HRV, it would be interesting to know if a resting pulse measurement, or maybe a measure of the orthostatic rise in pulse on standing from sitting, would have provide adequate information to guide training.
More recently Kiviniemi and colleagues have reported a similar study  in a group of 21 men and 22 women, with only a moderate level of preceding activity. In this study, HRV was assessed similarly, during 3 minutes of standing. The measurement employed was SD1 – the spread across the 45 degree line in the Poincare plot (as illustrated in my post of 17th July 2009). SD1 is a little easier to compute than high frequency power, but is closely related to high frequency power. The training program was for eight weeks. The standard protocol specified at least 3 high intensity sessions per week (the average number achieved was 3.3 /week) . In the males, the outcome was very similar to the earlier study: improvement in maximum output during testing on a cycle ergometer was significantly greater in the HRV guided group than the standard training group, though the increase in VO2 max did not differ significantly between groups. In the women, there was no significant difference between groups in the improvement in fitness, but the HRV guided group did fewer intense sessions. Again, it is clear that the HRV guided protocol detected over-reaching at least once per week, confirming that back-to-back intense sessions is undesirable.
In conclusion, the two studies by Kiviniemi and colleagues confirm that HRV guided training produces greater improvement in fitness than standard training that includes excessively frequent high intensity sessions. The question of whether similar improvement in training could be achieved more cheaply by manual recording of morning heart rate, or by more sensible coaching, remains unanswered.
Last summer, I was quite ill for several weeks, and as I recovered I faced the need to get fit enough to race a half-marathon in about 7 weeks time. I cautiously increased training intensity to include two moderately intense sessions per week (eg 5K at 80-85% HRmax) and a longish run. However I had not allowed for the degree to which I had been debilitated by my illness, and after about four weeks I began to feel quite marked fatigue. Measurement of HRV suggested that I was suffering from over-reaching. However simple measurement of the orthostatic rise in HR provided even clearer evidence that I was suffering from quite serious parasympathetic over-reaching. I usually have an increase in HR of about 8-10 BPM on standing from resting, but this orthostatic increase was abolished entirely as the fatigue developed, as shown in the figure.
I was able to implement adjustments to my training schedule that resulted in relief of the fatigue after about 2 weeks. In fact I was not completely recovered, as I will reveal in my next post, but my aerobic fitness was enough to run the half-marathon. Unfortunately due to inadequate number of long runs my leg muscles were not well conditioned and I tore one of my hip adductors after about 10 Km. I limped painfully with a stride that was very short and with virtually no airborne time, for the final 11 km. Despite this mishap, my experience is that monitoring for signs of over-reaching is indeed worthwhile, though my experience does not answer the question of whether or not it is worth investing in a HRM capable of measuring HRV.
But what about measurement of HRV while running? That is a far more complex question, which I will address in my next post*.
George Newton, the man who contributed much of the material regarding the interpreting heart rate recording during atrial fibrillation (AF) on the afibbers website , had left an interesting comment on my previous post on 27th June questioning whether my Polar RS800cx was a boon or curse. As illustrated in my post on 28th February, some of my chaotic recordings had raised the spectre of AF, but due to various inconsistencies in the data, I was left in a quandary. George’s initial conclusion was ‘Your data clearly looks like afib’.
AF is widely regarded as enigmatic and unpredictable, but in his own experience, George had found that systematic monitoring using various different methods ranging for simple manual recording of the pulse to recording the full ECG, can provide a large measure of control over the condition He has virtually eliminated his own AF by adjusting intake of electrolytes and other supplements according to the frequency of premature contractions, which at least in his case, are a fairly reliable indicator of imminent AF.
I myself have had several reasons for continuing to doubt whether or not I truly had AF. The most important piece of evidence had emerged during a recent relaxed run in delightful countryside in Leicestershire with my friend Marie (who had run in the London marathon with her husband a few weeks after she had been diagnosed with cancer, and has subsequently recovered well from surgery). During our run through the Leicestershire country-side I was feeling quite relaxed, but when I glanced at my Polar monitor I noted that it was displaying a heart rate around 125 whereas I would have expected a rate of around 110 at that pace. I immediately stopped to palpate my pulse. It was regular apart from the decreasing rate expected on cessation of running. There was certainly so evidence of AF, so we continued on our way.
When I got home I was dismayed when I examined the beat-by-beat record of my hear rate (the R-R tachogram). It indicated a horrible chaotic rhythm throughout much of the run – though frustratingly, it had failed to record the data for about half of the duration of the run, including the time when I had stopped to examine my pulse manually. The only absolutely certain conclusion was that my Polar RS800Cx was not storing data properly. It was impossible to determine if my heart was also malfunctioning. Nonetheless, the normal manual assessment during a run in which the recorded segments of the tachogram showed a chaotic rhythm raised serious doubts in my mind about the reliability of the evidence for AF.
I had also been puzzled by two other features of my chaotic tachograms. In the recording I had posted in February, careful inspection reveals that interspersed with the chaos are many brief periods (typically 5-15 seconds in duration) of what appears to be fairly normal sinus rhythm (figure 1). In fact the heart rate is a little higher than expected for the pace. Within the periods of apparently normal sinus rhythm, the average rate was 122 bpm compared with an expected rate around 115, but in the icy conditions on that December day, I would not have been surprised if my average heart rate was a little higher than usual as I struggled to remain upright. However, the heart rate variability is also somewhat greater than usual. At this pace, I would normally expect a value of RMSSD (root mean square of successive R-R intervals, a measure of high frequency variability) of around 5 ms, but RMMSD is in the range 10-20 ms during the periods of apparent sinus rhythm. I would usually compute RMSSD over a longer period than 10 sec, so this value should be interpreted with caution. Nonetheless, it suggests excessive parasympathetic activity. Thus my provisional (and very speculative) interpretation of the rhythm during this period is of a series of premature atrial contractions occurring against a background of sinus rhythm with excessive parasympathetic activity.
Secondly, on several of the occasions when I had recorded apparent AF, the average pulse was as low, or lower, than that expected for the pace. It is hard to imagine that a chaotic rhythm could pump enough blood to allow me to continue to run comfortably without any increase in overall rate to compensate for the inefficient ventricular filling.
With these uncertainties in mind I sent two of my tachograms to George – the one showing interspersed periods of apparently near normal sinus rhythm, and one showing a net decrease in rate. He was kind enough to search through his own records and produced a similar record which included periods of normal sinus rhythm interspersed within chaos. On account of the fact that his AF episodes are symptomatic, he was quite confident that this was not AF. He was also able to reassure me that overall rate would certainly increase rather than decease during true AF. Meanwhile Henry Szwinto, who had commented on my post of 5th June, had also sent me some traces of his experiences with AF while racing – confirming the dramatic increase in HR during AF. As an aside, Henry achieved 2:41:11 in the London marathon this year and was 3rd placed in the 50 year old veteran group.
So in this roller-coaster experience in which the evidence has swung to and fro, the pendulum is now swinging away from a diagnosis of AF, though I think that the evidence does suggest that I am prone to premature atrial contractions. There are still a few puzzles. Why did the early evidence indicate a strong association with use of the salbutamol inhaler which I use to control my asthma? As the evidence of chaotic rhythms has continued to accumulate, it has become clear that salbutamol was only associated with chaotic rhythm in winter. On some occasions when I had used salbutamol, I had noted in my log that the paths were icy, as in the run depicted in figure 1. Perhaps freezing temperatures increase the risk of both wheeziness and poor electrode contact; or perhaps salbutamol increases the risk of premature atrial contractions.
At this stage I am fairly optimistic that I do not have AF. I am still on the waiting list for a 3 weeks continuous ECG recording and I will await the outcome of that before attempting to reach a definitive conclusion. If the picture is still ambiguous after that, I will happily accept that some uncertainties in life are inevitable, and it would be foolish to limit ones activities for fear of vague uncertainty. The simple fact that elderly men have a substantial risk of AF already places me in a high risk group, and ambiguous evidence from a heart rate monitor scarcely adds to the level of risk.
With regard to the question of whether or not my HRM is a boon or a curse, I am fairly sure the answer is that a trustworthy HRM with the capability of recording R-R tachograms is a boon – although my unreliable RS800cx has been something of a nuisance. I did not send it back to Polar last week because I was eager to acquire as much information about both the behavior of the monitor itself and the behavior of my heart before relinquishing it, but I will send it back this week.
The important issue that this episode of chaos has brought home to me is the fact that for an elderly runner, the risk of AF is appreciable, and the consequences potentially serious. Furthermore, the experiences of George Newton, and others who have learned how to monitor their heart rhythm in an intelligent manner, is that paroxysmal AF is not necessarily an enigmatic mystery, but might be amenable to control.
And finally, while the association between endurance training and increased risk of AF remains a subject of debate, it seems to me very plausible that the sustained autonomic imbalance associated with over-training is likely to play a large role in determining whether AF becomes an intractable problem or resolves relatively harmlessly. I will return to a more detailed discussion of this issue in further posts, but meanwhile, I am more impressed than ever by the importance of avoiding over-training. So far, the evidence suggests that systematic monitoring of autonomic function by recording both HR and HRV is a useful way to minimize the risk.
So the answer to the question posed in my last post is that my particular Polar RS800cx was indeed something of a nuisance, but despite this, it taught me a lot, and I have little doubt that a reliable HRM with R-R recording capability is a worthwhile investment for any ‘serious’ elderly athlete*.
* For monitoring autonomic funtion via measurement of HRV to minimise risk of over-training; not for diagnosing AF, which requires a clinical-quality ECG recording interpreted by a qualified person.
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