What is cardiac drift?

Feb 5, 04 10:02

Post #1 of 17 (5003 views)

I have just begun training with a HR monitor since the end of December. I have done two step tests on my trainer in order to determine my LT. Both tests turned out well, clearly revealing my cycling LTHR was around 183 - 185 bpm. Also, the second test was shifted slightly, indicating I had better performance at a given HR.

So now I want to do some zone 2 work. According to Friel this is 152 - 165 bpm or so. I get on my bike and start warming up, easy at first and progressively harder, however, not too hard to induce any leg burning or heavy breathing. I usually notice an overshoot here, in otherwords I go a bit too hard so that if I continue at the current intensity I would be in zone 3, at this point I back off slightly (as my HR reaches 165). What I find however is that after some time at the current intensity I have to back off in order to keep my HR under my specified zone, and continue to back off until I finish my goal workout time. I presume that as the workout continues, my elevated HR is due to cardiac drift and/or fatigue. I've heard about cardiac drift, but I don't really know what it is exactly and how pertains to the above situation.

Do I need to try to stay in zone 2, or does zone 2 shift due to cardiac drift? If zone 2 is indeed shifting to a slightly higher HR, how much can be expected?

As a side note, I understand that the numbers 152 - 165 are not set in stone and that I need to use P.E. as a second indicator, but I have found that these numbers are in line with the corresponding R.P.E.

Thanks

---------------------------------------------------------

"What the mind can conceive and believe, the mind and body can achieve; and those who stay will be champions."

Re: What is cardiac drift? [Jack in Mi] [ In reply to ]

Feb 5, 04 10:40

Post #2 of 17 (4993 views)

jack. bring your trainer into a sauna. relax a spell in the sauna and then put on your HRM ( and your bike shorts) and climb up on the bike. what ho! your HR is already IN your training zone, you say? that is cardiac drift.

Re: What is cardiac drift? [Jack in Mi] [ In reply to ]

Feb 5, 04 10:51

Post #3 of 17 (4988 views)

cardiac drift is essentially what you perceive it to be - an increase in your heart rate over time due to constant physical exertion. basically, what is happening is that the efficiency of your heart is in fact decreasing over the duration of the activity. as such, the heart must either increase contractions (or beats) or volume (the amount of blood that is pumped per beat). decreased stroke volume caused by physical exertion in turn causes the heart to have to increase contractions in order to pump the same amount of blood. the heart really isn't getting "tired" per se but it is being forced to work harder because of environmental conditions.

the heart looses efficiency for a variety of reasons. the most common are heat, dehydration (or electrolyte imbalance) and simple muscle fatigue due to prolonged effort. as you train harder longer, the drift will in fact decrease, meaning your body should adjust.

i do not know of a definitive answer, but i would guess a zone is a zone and you keep within that zone regardless of the drift. essentially you slow down to enable your heart to work at the intended pace. why do i think this? because your lt is not drifting with it and the zones are designed to keep you in defined bands in relation to your lt.

hope that helps.

Last edited by: bryanjaf: Feb 5, 04 10:57

Re: What is cardiac drift? [bryanjaf] [ In reply to ]

Feb 5, 04 11:13

Post #4 of 17 (4968 views)

Thanks, that is inline with what I am looking for. I'd definitely like to hear from others also as to if they agree with your reasoning of staying in the zone. It makes sense and that is what I was inclined to think, but I wanted to make sure.

As a related question, I wonder if it is wise to aim for the middle of the zone at the beginning of the workout, which would allow me to keep my effort constant, while allowing the HR to creep 5 or so bpm towards the end of the workout. I tend to aim for the highest effort I can sustain and still remain in the right R.P.E. and HR zone, which almost always puts me on the high end of the zone. Any thoughts?

---------------------------------------------------------

"What the mind can conceive and believe, the mind and body can achieve; and those who stay will be champions."

Re: What is cardiac drift? [Jack in Mi] [ In reply to ]

Feb 5, 04 12:03

Post #5 of 17 (4946 views)

jack. with regard to environmental factors it is better to identify the factor producing the drift and eliminate it.

moreover, even tho your heart rate is elevated the workload is not. if you ride in a sauna at a cardiac drift produced HR of150 you will not be doing any work with your legs, for example.

thus, if you are riding indoors you should have a big ole fan blowing on you. without the fan you will be doing less work at the same HR.

Last edited by: t-t-n: Feb 5, 04 12:04

Re: What is cardiac drift? [t-t-n] [ In reply to ]

Feb 5, 04 12:59

Post #6 of 17 (4914 views)

Jack bryanjaf hit it pretty much on the head. The main external factors affecting cardiac drift are fatigue heat and resulting dehydration. If I might offer a view I share with my coach, You need to stay in your zone for an average hr but some over will not hurt the training as long as the average is in your target zone. When your working within a hr zone you don;t need to stay in one particular area because that is a range and you need to train the whole range of that zone and you also can train at what ever level within that zone depending how you feel on any given day ie if you feel particularly fatigued train at the lower end of the zone you will have a better feeling about the workout and not come off that workout evenmore fatigued. When racing and cardiac drift occurs it is not anything to worry about as long as your pe does not increase. My 0.02 hope this helps good luck mike

Re: What is cardiac drift? [Jack in Mi] [ In reply to ]

Feb 5, 04 13:21

Post #7 of 17 (4900 views)

I think the above posts did a good job of explaining cardiac drift - in laymen's terms it's your HR going up due to prolongeed exercise even at the same PE.

To answer your second question my bias is to stay within the heart rate zone. The reasoning is that you are doing a specific workout in a specific zone to achieve a certain result. Staying within that zone - be it an LT workout or an aerobic workout, you are training your body to train at a certain HR and if you veer from this then you aren't meeting the goal of the workout.

After reading your post and trying to understand what you are doing, I would say you need to start out a little easier. Warm up into your low Zone 2 and see how long you can maintain it. It takes discipline to keep your HR aerobic, and the very reason why many AGers don't improve. Most want to hammer or just be a 'little' bit harder then aerobic etc. Well, as long as you are training that way, I would be willing to be bet you won't improve much over time. Doing your aerobic base work in the aerobic zone is where you will get the most improvement. Most AGers shouldn't even be doing intervals since they have so much more room for improvement in their aerobic base - but that is whole other topic for another time.

Basically if your Zones are defined as 152-165 then keep it there. You'll see much more improvement over time. I hope this helps.

Mike Ricci
2017 USAT World Team Coach
USAT National Coach of the Year
Coaching Triathletes since 1992.

Re: What is cardiac drift? [bryanjaf] [ In reply to ]

Feb 5, 04 13:23

Post #8 of 17 (4899 views)

bryanjaf wrote, "do not know of a definitive answer, but i would guess a zone is a zone and you keep within that zone regardless of the drift. "

I don't think this is correct. You want to train at a level where the training stress elicits a certain adaptation (the training zone). The stress is defined by the power produced in training. Heart rate is merely one of the bodies responses to this stress and heart rate will rise or fall based on factors other than the training stress (e.g., heat in the sauna). Therefore, to produce the same adaptation, the same power should be produced, which means heart rate will rise as a result of cardiac drift.

Re: What is cardiac drift? [asgelle] [ In reply to ]

Feb 5, 04 13:38

Post #9 of 17 (4892 views)

Here is my problem with the counter argument. Let's say your LT is 170 and your Zone 3 is 150 - 165. The goal of a Zone 3 workout would be to work just below, or "in the range" of your LT without crossing the redline. Even if you experience a cardiac drift of 10 bmp, your LT has not changed, it is still 170. Thus if you move your Zone 3 tolerance to 160 - 175, you will be spending time closer, if not across to the redline, which is counter to the intention of doing a Zone 3 workout. Once you spend time over your LT you are eliciting a different adaptation.

What your advocating, I think, is training by power ranges rather than heart rate zones. Mike's post would seem to indicate that it is heart rate, rather then power that should define the sandbox perimeter.

Re: What is cardiac drift? [bryanjaf] [ In reply to ]

Feb 5, 04 14:19

Post #10 of 17 (4878 views)

"What you're advocating, I think, is training by power ranges rather than heart rate zones."

That is exactly correct. The object of the race is to cover the distance in the minimum time and all else being equal that means at the maximum power. Therefore, it makes sense that the purpose of training is to increase the body's ability to produce highest power over the duration of the race. Heart rate is only one response of the body to the stress of producing power.

Last edited by: asgelle: Feb 5, 04 14:26

Re: What is cardiac drift? [asgelle] [ In reply to ]

Feb 5, 04 15:04

Post #11 of 17 (4856 views)

The whole point of hr zones is to train that portion of your energy system. If you train out of that zone then that portion of your energy system is not trained. Yes the point in training is to develop power but to do this you need the aerobic base which is developed in zone 1&2 so you will have the aerobic capacity to produce more power when the time comes to do those workouts in zone 3 and above. If you don't train the aerobic system you can have mod to good results in sprint to probably oly distance but past that results may be in question. mike

Re: What is cardiac drift? [bryanjaf] [ In reply to ]

Feb 5, 04 15:05

Post #12 of 17 (4856 views)

Training zones are not about HR. They are about work effort. In the case of cycling, they are about POWER. HR zones are merely a guide to knowing what kind of power you are putting out. Even Friel makes this point in TTB, and provides the warning that slavish devotion to HR ranges is not a good thing. It is better to train on work effort. Since very few people have real-time access to work effort data when out on the roads (power or pace), then HR is the only thing available.

Think of a Zn2 ride as being at a certain power level, not HR. At that given power level (approx. 65-70% of threshold power), you HR will start out at some level and rise over time. The key to the workout is to HOLD THE POWER LEVEL. Let HR drift as it may. A Zn2 power level should be comfortable for several hours, day after day.

If you don't have a power meter, a starting HR for a Zn2 effort is likely about 75-80% of Threshold HR. Figure out what kind of pedaling effort that is, and hold that effort level as best you can.

As an example, I am doing "Level 3" workouts for 75 minutes once a week. The power is 210 watts. Last time I wore a HR monitor, my HR was 154 after about 15 minutes; 162 after 30; and 168 by the end (my "threshold" HR is somewhere about 174). The work effort was constant throughout, but my HR moved up from high Zn2 to low Zn4. PE only changed near the end (I got tired!).

It is the work done per unit of time that matters, not HR. HR is a slave to the former, and the former is what triggers training adaptations.

Re: What is cardiac drift? [ In reply to ]

Feb 5, 04 16:37

Post #13 of 17 (4837 views)

I think the role of heart rate and power in training is much clearer if we consider running or swimming. A typical swim set might be something like 4x400 on 5' with a target of 20" rest. Because conditions in a pool are more or less constant, all the efforts are being done at constant power. You don't see swimmers taking their heart rate at the end of each effort and adjusting the work time to account for changes in heart rate. Similarly on a track workout. Cycling causes a problem because conditions on the road are highly variable so it is difficult to maintain constant power without some measuring device. Because affordable heart rate monitors were developed before power meters, heart rate has come to be used as a surrogate for power. It's interesting to note that on the velodrome, where conditions are fairly constant, workouts are specified by lap times, not heart rate.

Re: What is cardiac drift? [Julian] [ In reply to ]

Feb 5, 04 17:19

Post #14 of 17 (4829 views)

I understand what you are saying and it makes sense at an intuitive level, however I can't say I know of many AGers who are training by power. In my view Friel is speaking to a higher level of athlete then I when he talks of the concept. The truth is that you can't be a slave to any device you need a combination of data and feel. However, I am of the mind that the average AGer trains too much at high intensity levels and fails to work on the aerobic base necessary to achieve large gains when speed/power work is incorporated into the training regiment. Thus sticking to ranges and constantly recalibrating such ranges is not in itself a bad training guide, in my view.

Re: What is cardiac drift? [asgelle] [ In reply to ]

Feb 5, 04 17:24

Post #15 of 17 (4828 views)

I agree with you that swimming is guided much more by power then HR but Friel, if I recall correctly, advocates establishing a link between heart rate and 50 m lap times. Thus the set can be designed to keep the HR within a certain zone.

Re: What is cardiac drift? [bryanjaf] [ In reply to ]

Feb 5, 04 17:57

Post #16 of 17 (4819 views)

Heart rate alone is not the best indicator of training workload. (glycogen levels, fatigue, sickness, environmental stress all may cause HR to fluctuate up or down during exercise)

Perceived exertion has been shown to have a much greater correlation to LT and VO2max as well as submaximal intensity. Heart rate shows the load on the whole cardio vascular system not only the transport to the muscles.

When you have heat/environmental stress (and thus cardiac drift) part of the heart rate is accounted by the bodies attempt to disipate heat [as well as an effort to maintain the cardiac output (by increasing HR)] due to dehydration.

Just becaue the HR is elevated above a target range, it does not mean that the work load by the muscles is above the range. This is where power (for cycling) and perceived exertion are the best tool for gauging intensity. The fact that there is cardic drift (and by how much) is an important factor. If you are dehdrated then it wont be long before performance suffers.

Re: What is cardiac drift? [bryanjaf] [ In reply to ]

Feb 5, 04 21:57

Post #17 of 17 (4781 views)

Quote:

However, I am of the mind that the average AGer trains too much at high intensity levels and fails to work on the aerobic base necessary to achieve large gains when speed/power work is incorporated into the training regiment. Thus sticking to ranges and constantly recalibrating such ranges is not in itself a bad training guide, in my view.

I very much agree with you. Absent some feedback tool, many people will go too hard and not be able to sustain consistent, long-term volume. I still wear my HR monitor on the long run and the long ride, and for the simple reason that it keeps my enthusiasm in check in the early going. Around the halfway point, I start watching power (on the ride) and pace (on the run) to make sure I'm not slacking off. By then, I'm pretty dialed into the right effort level for that day and switch off the HR monitor.

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