The answer may be more complex, as it is well known that resting heart rate decreases with increasing fitness. As an anecdotal observation when I was younger and took part in rowing, I was very fit and my resting heart rate was 45 but my maximum achievable heart rate (measured on an exercise bike) was 160. I could not get it higher. By contrast one of my fellow rowers had a resting heart rate somewhere in the 70's but his maximum heart rate was 220, but I would have said he was fitter than me. I suspect that it may be possible that the maximum heart rate does not change much but the system becomes more efficient as the resting heart rate lowers and the heart may be able to pump more blood per stroke. The only way to find out is to test it, which a sports physiologist may have already done.

In my opinion you have to distinguish between mental und physiological changes. Speaking about mental aspects, the athlete will be able to sustain pain/discomfort over a longer period and will also be able to increase maximum achievable HR. On the other hand, exercising the same training program every day, will either lead to overtraining or stagnation/decrease in performance. When I am in a approaching overtraining or overreaching, I noticed that HR during exercise decreased. However, this will be individually different. As Jerry said before, you have to test it in a cohort of trained cyclist to get the "right" answer.

As a general rule, as Jerry stated above, maximal heart rate (HR) declines as 1) we become more fit and 2) as we age. HR is 1 component that makes up Cardiac Output, with stroke volume being the other. As our bodies become more fit, so does the heart and stroke volume increases (which Jerry also indicated), with Cardiac Output also increasing. Because the stroke volume increases to a substantial amount, the heart does not need to beat as fast. Cardiac Output is what is important. It is not as though the maximal HR is painful itself, but rather that at those intensities you are near or above your anaerobic threshold and will be accumulating hydrogen ions to a greater degree. That hydrogen ion accumulation (i.e., the accompanying acidity), in addition to the physiological limits of the muscles (from a metabolic and sliding filament theory standpoint) are what are triggering pain. Each person has a different "pain tolerance", and it is common to see an individual increase their "pain tolerance" as they become more fit and familiar with fatigue/exertion/pain. Remember that the brain is likely to trigger you to stop exercising (or at a minimum to lower the intensity) well before your ACTUAL physiological limits, so the perception of pain and the actual tolerance will change with familiarity and should increase with increased fitness. I hope that helps. 

Hello,

I would tend to disagree with Gustavo regarding the effect of aerobic training on max heart rate (HR), see: http://www.ncbi.nlm.nih.gov/pubmed/17960504

Would it be worth focusing on HR reserve to account for the potential changes in rating HR?

Best

julien

I think we have to be cautious about inferring about change from cross-sectional data. Lower HRMax in trained athletes does not demonstrate that training decreases HRMax. The only way to demonstrate this would be to conduct an experiment showing changes in HRMax following a period of training. Even then, it is difficult to tell whether change is valid, because of the difficulties in determining whether volitional maximum (volitional = subjective decision to stop) is true physiological maximum.

Additionally, I can say: if the person undertakes a program of high-intensity interval training (HIIT) and the load is determined by max HR of the first training day this could be a mistake (eg. if you don‘t used this high-intensity load in familiarization). I don‘t know how really max HR changes as the program progresses, but I can say that already on the second day of training is more difficult to reach max HR. It manifests in all unexpected activities (physical load, temperature adaptations and so on).

If "maximum achievable HR" is much lower than the age predicted maximum HR, I expect it increases with high intensity exercise training as with fitness level improvement, one could exert more to a HR approaching his/her maximum HR.

For a person who is already reasonanbly fit, further training can improve exercise performance (loading) with the same maximum HR (anaerobic training).  

Discomfort/pain is not solely determined by HR, it is related to fitness level, muscle power, peripheral circulation, oxygen uptake capacity and level of lactate accumulation, etc.

Usually we don't need to achieve maximum HR for most of the training. We can use maximum HR to classify the intensity of exercise training.  For high exercise intensity, the peak HR should be >85% of maximum HR, moderate exercise intensity is 60-85% while low intensity is

The maximum achievable heart rate , HR max, of an individual is fixed and decreases with advancing age. When someone does intense exercise his/her HRmax can be achieved  earlier and that person who does the very intense exercises will work at close to this value for the period of intense exercise.

A person who is in a detrained state will also achieve heart rates close to HRmax on starting exercise programs (by doing relatively easy tasks) but as fitness increases the intensity of work required to achieve HR max increases.

In a nut shell HR MAX does not really increase at high work loads but a fit person is able to tolerate more work for longer periods at the HR max than an unfit person and also requires a higher volume and intensity of work to achieve this HRmax than an unfit person.

Does the 'maximum achievable' heart-rate change as cardiovascular fitness increases in response to HITT?

What factors, known to regulate and control heart rate, can be changed by HITT?

Sounds like a great study Hugh.

I wouldn't be as categorical as Terence regarding HRmax being "fixed".

I'm not sure there is a clear answer with HIIT, but there is strong evidence (in animals) that under some circumstances HRmax can change. Fro instance, Favret et al. (2001) demonstrated that chronic hypoxia can lead to an up regulation of the muscarinic receptors and a down regulation of the adrenergic ones in the heart. Both of these changes were correlated with HRmax.

Best

Julien

Reference:

Favret et al. (2001) Am J Physiol Regul Integr Comp Physiol. 280(3):R730-8. Myocardial adrenergic and cholinergic receptor function in hypoxia: correlation with O(2) transport in exercise.

Thanks for all your responses! This is what I have learnt ...

1) What I referred to as his maximum "effective" heart rate is his maximum heart rate. I had just assumed they were different because it was so much lower than the predicted HR_max. But all HR_max predictors apparently have a huge variance.

2) It doesn't look like there is any consensus here on whether HR_max should increase or decrease as a HIIT campaign progresses. So I'll take an average of the responses and assume it remains constant, which is pretty much consistent with what I have observed.

3) I was surprised how little difference there was (on average) between the HR_max of fit and sedentary people reported in the literature.  e.g.

"Greater rate of decline in maximal aerobic capacity with age in physically active vs. sedentary healthy women" 

and

"Training Induced Changes in Maximum Heart Rate"

Differences between the lines of best fit are small and the dispersion around those means is huge. So there are lots of variables at work here.

4) With all of this, the measured HR_max surely depends on the subject's willingness to push him/her self to the limit and to stay there for a while, which is not a pleasant experience for most people. And yes, boredom may be a factor if the same HIIT activity is performed over and over for a long period of time.

5) I probably should have paid more attention to the power output (on the exercise bike) when HR_max is reached and how long it can be maintained (i.e. total energy expended) then monitored how that changes as the HIIT program progresses. From what people are saying, it sounds like that is more likely to change (increase) than HR_max.

Thanks again,

Hugh

Update ...

As this training regime/program continued, I did not notice an increase in HR_max from what had been observed earlier on in the program (beyond 150 bpm). Of course, It's hard to know if the subject quit and 'slacked off' as soon as he saw that the 'limit' had been reached. However, towards the end of the program, on some occasions, it did look like the peak power output (around 355 W) was significantly greater at HR_max, than it had been earlier on in the program (around 315 W).

The subject did go on to win the event for which he was training, which requires extreme anaerobic and aerobic exertion, so it would appear that this approach (exercise bike in the gym) is a suitable replacement for running (to avoid jarring of joints) and cycling on the road (to avoid being hit by cars).

I still think about this every day. OK, every weekday. OK, every other weekday. My current thinking is that HR_max may indeed be fixed for a given individual at a given age. When you are fit, it is hard to get there; when you are not so fit, it is very easy to get there (if you are sufficiently motivated). 

Based on my personal experience in running it did increase with exercise.

I started training for a marathon a year ago. My training, averaging 6 hours a week, mainly consisted of a lot of easy runs, then gradually incorporating tempo runs and interval sessions. As a 36 years old man at the time, my HrMax was supposed to be 184 bpm. That was true at the beginning of my training as I was only able to achieve 182 bpm with an all out effort. Within months of training I realized that my resting heart rate dropped from 80 bpm to low 50 bpm and my overall performance improved. At the same time as I started training more and more intense tempos and interval runs, I started reaching higher and higher heart rates. First I achieved 187 bmp during an interval session in an all out effort, followed by 192 bpm in a 3K time trial about a month later. Convinced that I could go higher than my theoretical limit, I trained harder(more volume and intensity) the following weeks. However I was not able to achiever higher heart rates and I was overtraining. So I took a short break. When I came back a week later, I achieved 197 bpm in an interval session. So I realized that the more I rested between my sessions, the more I was able to achieve higher HrMax.

Today my HrMax stands at 204 (that I achieved last week) which is way above my current theoretical 183 limit(as I am no 37) and I am still under the impression that I have not reached my limit yet...

For me the bottom line is: while low heart training improves the overall aerobic performance, high intensity training combined with proper recovery can train both the mind and the heart to reach higher achievable Hr Max. That was at least the case from my personal experience

Anecdote does not equal evidence. All this talk about how people differ (my fit friend vs my unfit friend), or personal experience (my experience training for a marathon) is weak evidence, because it is based on small samples (N=1!) and unsystematic observation.

Also, logic can be applied in both directions. "Unfit people find it easier to get to max, because it doesn't take much to get them there", vs "Fit people are more able to sustain difficult intensities in order to reach max, whereas unfit people give up before they reach max".

In terms of empirical evidence, I'm not aware of a single study that shows convincing evidence that training leads to an increase in biological maximal heart rate. In people, not animals, that is .....

As Siragbsou indicated, though, training may enable an individual to more likely reach their true maximal heart rate. But this doesn't mean that biological maximal heart rate has increased.

Sirgabsou Yandika I think HR max is an indication of how hard you are trying, or how much suffering you are willing to endure. Yes, having a break between workouts can help with that. I think energy output or distance travelled for a fixed time interval are a better measure of cardio vascular fitness (in my opinion). The rate at which the HR falls from max, during the cool down is also a good indicator of fitness, as this does not depend on motivation or effort, is just physiological. There is also HR measurement error to consider. Sometimes HR monitors can get confused and lost. Rapid changes in rate, up or down, are a warning sign.

This may have already been shared and is not a direct comment on the answer to the original post, but I believe there is an equation other than 220-age for max heart rate that involves heart rate reserve and uses the resting HR in the math. I believe it was developed to be more "personalized" since it takes one's fitness into account whereas 220-age does not.