Relationship between HR, power, anaeric threshold and rpm

Aaberg

Some data about me:

Max HR: 200bpm
Anaerobic threshold: 172bpm (lab test)
Power at threshold: 250 (lab test)

Today I did 3x8 minutes of intervals at 225 watts on my Tacx I-Magic.

Here's my average pulse and cadence at the three different intervals:

Interval 1: 80-85rpm, average pulse 161
Interval 2: 80-85rpm, average pulse 171
Interval 3: 100-105rpm, average pulse 192

The data shows that even if I'm training at a power 10% lower than my threshold power, my average pulse during the last interval (caused by a high cadence) is higher than my threshold pulse.

So, my question is. Am i "actually" working out "below threshold" during my last interval? Or am I working above my threshold?

If I want a "below threshold" workout, should I restrict my cadence during the last interval?

Both answer to my questions and general comments are welcomed!

Thanks,

Aaberg

Steve McGregor

There are a couple of things to consider here. First of all, it is difficult to come to a conclusion about the HR response to your intervals because you performed 3, and the HR was higher in the third. This is to be expected due to typical cardiovascular drift, where HR increases over time at a constant workoad. To get a true answer to this question, you should do multiple trials where you alternate the order of the cadence intervals. So, if you saw the same response when the high cadence was first, that would be more conclusive. Second, was the AT determined on the same trainer? The accuracy of the Tacx trainer is questionable, although, from what I hear, data may be reproducible. So, the question becomes, where you actually 10 % below your "threshold". The reason I use quotations is because a lab determination of the AT is oftentimes diffferent than what most people consider the LT. That's fine as long as you use your AT as the reference point.

All of these things being said, it is typically observed that when cadence is above 100 rpm, HR rate is higher at the same workload than lower cadences (e.g. 85). There could be a number of explanations for this (e.g. # motor units recruited, frequency of stimulation etc..), but suffice to say, it is not unexpected. This is one of the drawbacks to using HR to measure intensity because there are a number of factors, within the context of one workout, that would effect it.

So, the question becomes, why are you altering cadence? And.. why would you restrict it? As you train with power, you should realize that if your threshold power is 250, and you want a sub-threshold workout, 225 watts is below your threshold. The HR is kind of irrelevant. That's not to say, of no value, but less relevant than the power itself. So in your example, all intervals were below threshold. One interval appears to have elicited a significantly higher HR, and there may be a reason for that, but the sub threshold is sub threshold. This obvioulsy leads into a discussion of the value of cadence limited workouts.... That's for another thread.

Steve

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beerco

Good answer Steve. Since this isn't wattage I'll ask: of what value is HR? Be specific, use real examples

(really, I'm not trying to start a battle but I've yet to hear a good story* where power + HR led the rider to do something different than power alone would have)

(* one guy on this site once told me that an elevated HR at threshold meant he was getting sick and bagging the workout could help him avoid the cold entirely - very difficult to verify).

Steve McGregor

Somebody's always got to poke me with a stick Well, you're right, this isn't wattage. I'm not going to provide anecdoctal evidence or get into an academic debate. I'm sure we both agree that power is the most important, accurate measure of cycling intensity. The simple answer would be that, over time, you would expect, as with other variables (e.g. PE, ventilation etc) to go down in relation to a given workload. This would be a big picture response to improved fitness with training. Whereas, if HR were going the other way, consistently, and other factors (e.g. PE, Ve etc.) were also, you might get the big picture that something is wrong. Since you obviously frequent wattage, I'm sure you're more than likely of the opinion that power tells most of the story, and it does. But for those who do not train exclusively (I like to call them hybrids) with power, or are multisport athletes, HR is still a valuable tool. Not as accurate as power, but not entirely useless either. With several of the triathletes I have worked with for example, who use computrainers, but not portable power meters, we use a customized version of TRIMPS. It does a nice job of tracking training stress, although needs to be taken with a small grain of salt. That's the best I'll do for now. Sorry if it doesn't start a AC vs WG firefight

Steve

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Aaberg

Thanks for your comments. They were helpful.

Given that my Tacx trainer is reliable and I'm actually working out below my lactate threshold, and suppose I do workouts like this 2-4 times per week and regularly experience that my heart rate is well above my lactate threshold HR. I will not risk peaking to early in the season? Or experience a burnout as a result?

I'm "safe" as long as my power is below my threshold power?

Aaberg

Steve McGregor

Of course burnout or whatever you wish to call it is dependent upon various factors. If these are the most strenuous workouts you do, and you do them 3 x per week, you should not "burnout" or be overtrained.

Steve

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Steve McGregor

Aaberg,

I need to add to my response from last night. it was late and I have been sick and probably not thinking clearly. First off, I go back to the original question about why are you doing intervals at this power and cadence? Does your discipline require it? If so, fine. Some might question if there is value to them. That being said, if you are actually performing them at 90% of your workload threshold at a lower cadence (e.g. 85 rpm), then the actual metabolic requirements of the bout may be over your threshold. So, although your AT was determined to be 250 watts (@85rpm?), 220 may be your threshold at 105 rpm. Make sense? Hard to say without more extensive data. So, back to my response from last nite. Do I think putative threshold workouts at 8 min each performed three times per week will burn you out? Depends.. but without other severe workouts, no. I'm sure the Wattage police will pick me up for this one some time this evening, but there you have it.

Steve

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Aaberg

Thanks again Steve and beerco for your comments.

Yesterday I did the same workout as the first one, but I moved my "high cadence interval" to the beginning of the workout.

First workout (Three days ago):
Interval 1: 80-85rpm, average pulse 161
Interval 2: 80-85rpm, average pulse 171
Interval 3: 100-105rpm, average pulse 192

Second workout (Yesterday):
Interval 1: 100-105rpm, average pulse 174
Interval 2: 80-85rpm, average pulse 179
Interval 3: 80-85rpm, average pulse 181

Just like you commented, it seems that higher cadence results in a higher heart rate, and there also seems to be a little bit of cardiac drift. Is this a fair conclusion?

So what you're saying is that my power threshold and HR threshold varies with respect to cadence? If this is the case then I guess our friend beerco has got his good story?

If my training at a given power have different results (sub-threshold vs super-threshold) depending on cadence and HR, then the analysis of my power+HR would lead me to do all my intervals at this power at 80-85rpm in order to keep the workout sub-threshold, right?

Steve, one final, question. It seems to me you are refering to wattage as something different than power. Wattage is what you use to measure power, right? I don't understand that there is a difference? Or did I interpret your comment to beerco wrong?

Aaberg

Steve McGregor

Well, as I said before I inadvertantly deleted my entire response, this is a step in the right direction to finding the answer. To me, your data indicates there is CV drift over the course of your intervals. I'm not sure if I would conclude the HiCad intervals elicit a higher HR. There are a number of things that could contribute to a HR of 174 vs 161. Was warm up identical, was temp identical, sleep etc.? There just aren't enough data points right now. If you are really interested in finding an answer to this, I would suggest repeating this approach in the next week, i.e. HiCad at the end one day, HiCad at the beginning one day, and keep as many things as identical as possible. If you saw the same trends after two more trials, that would tend to confirm your conclusions.

What I was saying is that we know at cadences above optimal, we are less efficient. That we consume more O2 to do produce the same power, and hence see higher HR. So, if your optimal threshold is 250 watts at 85 rpm, you will not be able to produce the same power at a cadence of 120 rpm and remain at steady state, and HR will be higher, as will some other variables (e.g. ventilation and PE). The question then becomes, if you train at 225 watts and 100 rpms, will you improve your threshold at 85 rpms, and at 100 rpm? If not, is it of value to train at 100 rpm?

Yes. But again, the question becomes, what is the motivation for training at those cadences? If you need to ride at 100 rpm, then by all means you should train at 100 rpm. If you produce optimum power at 85 rpm, and do not need to ride/race at higher cadences, then you may want to consider simply training at 85 rpm or close to it. The thing is, we typically choose our optimal cadence for a given power. So, if you need to produce 250 watts for an hour, you will likely choose 85 without thinking about it. There is debate about whether or not performing HiCad intervals below a given workload will result in training adaptations at higher workloads relevant to that cadence. Some don't think there is a debate.

Sorry, Beerco and I were likely referring to the collective consciousness known as "wattage", which is a group of very intelligent (for the most part), critical thinkers, that wile away the day discussinig these types of issues (power releated) ad nauseum. You can check it out at this link.

http://lists.topica.com/lists/wattage/read

Steve

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dkxkvtr

Some additional thoughts on this issue:
1>) there needs to be adequate rest between each interval (at least a full 5 min in zone 1 and 2) and between sets (usually two intervals per set) for a full 10 min in zone 1 and 2.


2.)AT intervals should always be around your AT heart rate. Cadence and power are adjusted accordingly to achieve your AT Heart rate. There are specific physiologic reasons for this which i will enumerate. Functioning at prolonged periods at your AT (10 min or more) stimulates specific chemical mediators that promote mitochondrial biogenesis(produce more mitochondria).
Mitochondria are the power house of the muscle. the more mitochondria, the more oxygen your muscles can process the more ATP (energy) you will produce and the more ATP the more power you will be able to generate.
THEREFORE, functioning at AT intervals will ultimately (approx. 6 weeks of training) produce more power NOT visa versa. In order to produce more mitochondria it is imperative that you stay in and around your AT. This is essential!!

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in.10.city

Another thing to consider is your pedaling efficiency at the higher cadences. If your legs are flailing around and your muscles are doing a lot of choppy relaxing and contracting, then your HR will elevate much quicker. Your HR will probably be higher at the higher RPMs, but a smooth and supple pedal stroke will elicit less of a HR spike.

beerco

Who the heck are you and what makes you think that power should be adjusted to hit your "AT" HR?

Intervals done at a constand HR are really decreasing power intervals e.g. if you start at 250w at say 150bpm, by the time 20 min have gone by you will have dropped power to hold that 150bpm.

Steve McGregor

? Based on what criteria?


Boy...., you do realize this is a power forum, right? I would recommend you check out the FAQ at the "wattage" link I provided earlier. You're right, there are numerous physiological adaptations (most notably increased mitochondrial enzyme activity) that occur as a result of training at or near our LT/AT, or whatever you want to call it. These adaptations do not really rely on HR, and power based workouts should certainly not be _based_ on HR. That is the value in using a power meter to train and monitor progress. Power based training protocols are much more accurate than HR based protocols, and typically more effective at eliciting desired responses. The primary argument against using HR based protocols is the clear evidence of cardiac drift that most people realize once they start using a power meter to train. Cardiac drift is a rise in HR over the course of a bout at a give workload, or even reduced workload. So, over the course of a set of intervals, your HR could climb by as much as 5 or 10 bpm, or even more, and workload would stay the same. An even more insidious scenario is the one where you go out and do a long set of intervals and nail the HR on the head for the whole set (and as a result, you're feeling pretty good about yourself), but over the course of the intervals, you power went down 10-20 % because you were holding HR constant. So, instead of doing L4/AT intervals, you ended up doing L3. As I said a couple of posts ago, there may be some value in monitoring HR during, or after, training, but basing LT intervals on HR is not one of them. I think if you looked over the FAQ for wattage, you might benefit greatly.

My .02
Steve

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Steve McGregor

Oh.. I guess Beerco beat me to it Although, constant HR intervals need not be decreasing power intervals. L3 intervals under thermoneutral conditions with sufficient airflow could elicit steady state HR. If you want to call L3 work intervals. But, if you've got a power meter, you might as well be sure.

Steve

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