Cardiac drift?

[jeffg]

Anyone care to expound on what this phenomenon means for gauging effort? It makes sense that one's HR would gradually increase in response to sustained efforts, especially in the heat; however, I am not really sure what the implications for training are. Thoughts (Dr. Doofus)?

[Needs Help]

Anyone care to expound on what this phenomenon means for gauging effort?

From triathlete.com:

Cardiac Drift can loosely be described as the increase in heart rates over a longer period of time for a constant physical output. This may occur in cycling, running and triathlon and as anyone who has done an Ironman would know, quite dramatically during the IM marathon. To understand cardiac drift we must first understand cardiac output. Simply put cardiac output is stroke volume (the amount of blood your heart can pump in a given contraction) times heart rate (the frequency at which your heart beats, usually expressed in beats per minute) Cardiac drift primarily is the result of decreased stroke volume thus causing your heart to work at a faster rate in order to meet the metabolic needs of exercise. A decrease in stroke volume during exercise may be caused but is not limited to the following:

Excessive heat
Increased sweat rates
Electrolyte imbalance
Decrease of venous blood return to the heart
Decrease in muscular economy due to fatigue

During exercise demand for blood volume to working muscles increases, and conversely both heart rate and stroke volume increase to match the demands for a given workload. In other words the physical demands of your activity initially dictate cardiac output. However during long periods of activity and in this example I will use Ironman, many factors will conspire against you :

-Increased blood volume to your skin in order to facilitate cooling: Say you are in the starting stages of the IM run and it is cloudy and 75 degrees, you are running smoothly and all is well. All of a sudden everything clears and it is 105 in the shade. Watch out! Your body will divert as much blood as required to the skin to assist in cooling. This blood will come primarily from non-essential sources such as your legs and arms. Basically your brain is telling your working muscles to tone down the party and give some of that blood back to your skin or else the party is over for everyone. Reduced blood volume available for working muscles means that the remaining volume has to circulate faster (increased HR) at a given workload to feed the muscles oxygen and carry away waste products.

-Decrease in blood volume through sweating: Not only is there a diversion of blood volume to the skin in order to cool the body there is also an overall loss of blood plasma through sweating. Even among the most diligent and hydrated athletes there is always at least a slight loss towards the end of the race. The result is a thickening of the remaining blood volume therefore placing greater demands on the heart. To pump the same amount of blood volume the heart has to either contract more forcefully or more rapidly (increased HR)

-Electrolyte imbalance: As we all know electrolyte balance is critical to muscle function and endurance sport in general, however it is particularly important to regulating the contractile force of your heart (your heart is also a muscle). The larger the contractile force of the heart the higher the stroke volume and the lower the heart rate at a given workload.

-Decrease of venous blood return to the heart: During prolonged periods of upright exercise such as cycling and running there is a slight decrease in the amount of blood returning to the heart. This may be caused by a slight increase in blood accumulation in the legs or by the first two factors mentioned. The overall effect is once again a loss in available blood volume for working muscles and a decreased stroke volume for the heart.

-Decrease of muscular economy/efficiency due to fatigue: A primary function of working muscles is to facilitate, through contractile force, blood flow back to your heart - in effect "pumping". As exercise duration increases muscles eventually become less efficient and contract less forcefully. There are a million reasons for fatigue during exercise but the results of fatigue and reductions in economy are always the same : Less venous return back to the heart, decrease in stroke volume, increase in heart rate and energy requirements for a given pace or workload.

So what does it all mean?

Outlined above are some causes for cardiac drift and how it may effect performance. All well and good, however the information is useless if you can't apply it practically. The following are just some suggestions and strategies which I have found useful:

Acclimatize!
If you are coming from North America and planning on doing IM Malasia, Australia or a mid winter race somewhere hot you have to allow yourself the appropriate time to adjust to the heat. For Ironman I believe the greatest gains are made when you have the opportunity to do a couple longer and more intense workouts in the heat of the day. This is a lot more specific and practical than hanging around the beach hoping for heat adaptation. For myself the minimum time to acclimatize is about ten days.

Drink!
Not much to say here, everyone knows how important hydration is. The thing to remember is that hydration regulates blood volume and thus regulates heart rates and performance.

Maintain electrolyte balance!
This is different than hydration. It is critical that you determine exact individual electrolyte requirements during training. Don't take two grams of sodium an hour just because you heard some pro did it in Kona. Every athlete and race situation are different, personally I drink water on course and take an essential electrolyte pill as required depending on how I am hydrating. This strategy allows me to monitor my hydration and electrolyte intake and adjust depending on heat and other factors. For food I use my own carb drink and gels. Basically this gives me a pretty complete picture of what's going on and allows me to modify intakes to meet the conditions of the race.

Hit the weights!
A properly periodized strength program is critical to endurance sport. And if done correctly will increase strength, range of motion, and resistance to injuries later in the season. If done incorrectly will cause nothing but problems and setbacks. I recommend people find a local expert to help with form and posture. Stronger and more efficient muscles will theoretically either increase venous return to the heart and/or require less blood volume at a given workload. Your soleus muscle(calf), sometimes referred to as your second heart may have an increased role to play in the capacity of venous return. One could theorize that increased soleus function would play a critical role in moving blood and therefore offsetting cardiac drift. For me this is just an Idea and I could not find any studies which could specifically correlate dramatic increases in soleus size or function to performance. So don't go out and work your calves to the size of grapefruits, simply include them along with everything else as part of an all body strength program. Keep in mind that your program has to be specific to endurance sport.

Don't be rigid with Heart rate zones!
If you stay religiously within a 5 beat "zone" for all of your long workouts the net result will be a gradual slow down over time. Not exactly the desired effect or what you want to happen during a race. Typically for longer workouts I stay within a 5 beat zone for the first half and allow my HR to drift upward during the second half while maintaining an equal pace or output for the whole workout. Don't worry you are not going to go anaerobic and collapse. For me this drift is only about 10-15 beats over the period of a long run and only about 5 beats higher during my final long workouts approaching Ironman. I stay away from Heart Rate monitors while competing, preferring to race by feel.

Focus!
When the going gets tough it is important more than ever to concentrate on form and economy, especially proper arm swing. This is one of the first things to go when people get tired, the second is usually their sense of humor. Remember that you did not train ten months to be derailed by a bad patch. In Ironman they happen to everyone throughout the day, the important thing is to stay positive and focus on foot strike, arm swing and being efficient.

To summarize (we could go on forever) I think it is important to realize that cardiac drift is a function of many factors both external and internal most of which we can control and minimize. Cardiac drift is not the heart getting "tired" it is the rest of your body adjusting to conditions and becoming incrementally more inefficient. When looking at drift I was hoping to find some information which would say "this is how you minimize it", perhaps a tidbit of information which would provide some performance gains or point out possible training errors, I found no such hard evidence. Basically it comes down to what we all knew in the first place : Train to meet the stresses of your event, keep cool and hydrated, stay positive and enjoy the day!

[Chief]

Very interesting and insightful Needs Help! :)

[jeffg]

the question is still what to do when you note your HR is climbing when the load remains relatively constant? The article seems to leave that unanswered. hmmm

[Needs Help]

the question is still what to do when you note your HR is climbing when the load remains relatively constant?

Based on the article, I would drink a personally tailored brew of electrolytes and concentrate on efficient pedalling.

[Andreu]

My interpretation, for what it is worth, is that overall efficiency of the body´s systems decrease (I have heard that blood thickens slightly due to the loss of water too) the result is that the heart has to work even harder to maintain function through the later part of a work out. If stroke volume is decreased then the heart also has to pump faster to maintain the work the body is doing.
Well it makes sense to me anyway.
A :bike:

[Too Tall]

"Don't be rigid with Heart rate zones!"

Above quote is salient in so many ways. You won't know what you are looking at unless you have kept good records and are already experienced with training HR zones AND know when to expect it.

At this point in my training I don't even ride with the HR strap and just track watts and keeping tuned in to perceived effort.

The most useful thing I do use HR for is to stop myself from riding hard when I'm supposed to ride easy.

[csb]

often occurs after said steel yacht passes
and then wanders over to the right, crossing
into the path of the cyclist just passed.

[soulspinner]

Years ago we called it cardiac creep-same thing you described above. Hydration seems to be the key for me. If I remember to drink before I ride on hot days it helps. When Im hydrated my pulse recovers(comes back down) more quickly as well.

[Ken Lehner]

At this point in my training I don't even ride with the HR strap and just track watts and keeping tuned in to perceived effort.

Just curious: if you don't mind, I'd like to know the kind of wattage a big old guy like you puts out for TTs and other workouts. How old and big are you? What power meter do you have? You seem to have pretty good racing results.

I'm 46, 170lbs, with a Power Tap.

[dohearne]

An ancillary question to this thread is one regarding maintaing a target HR within a narrow range. Although I am not obsessive about my HR, I do usually decide to be within a certain range for the majority of a particlular ride. However, if I can stay within that range for more than 50 percent of the time I consider that quite good. This is with using a range which for me is usually 15-20 beats wide. I have read some who recommend ranges as narrow as 3-6 beats. However, I find my HR to be very sensitive to even very slight changes of terrain, and gear changing and effort has to be modified considerably to compensate. I know elite riders have finely attuned bodies, but I just don't believe that our cardiovascular physiology is as controllable as some would have us to believe. Any comments?

[Andreu]

I have read some who recommend ranges as narrow as 3-6 beats. Any comments?
I would say 3-6 beats is too narrow. The machines we use probably have error associated with them of say 10% (this is typical of many electronic measuring devices....) so expect error of say 10 beats minimum. I am not sure if this error is increased as the heart speeds up. I'd say your 15 to 20 beats was probably a good way of going about things if thats what you want to do. Anyway, maintaining HR within a narrow range is impossible on the roads around here (very hilly)!
I use my HR moniter as a rough guide sometimes...I have not used it now since early February because it can confuse the issue and take some enjoyment out of cycling. Some people live by their rate. I know when I am f***ed and have to rest.
A

[Michael Katz]

A related issue to heart rate is how you determine the range you want. Different methods produce different ranges of beats per minute even though the "percentage" looks the same. Edmund Burke, in the book Precission Heart Rate Training, discussed how the "Heart Rate Reserve Method" of calculating target zones is superior because it actually tracks percentage of VO2 max and that it is really the ability to use heartrate to measure VO2 percentage that provides accurate training feedback. It is the percentage of VO2 max that provides the training effect, not mere heart rate, otherwise sitting in a scary movie and having our hearts race would have a training effect!

The formula for calculating target zones using Heart Rate Reserve is (Max Heartrate - Resting Heartrate) x desired % + Resting Heart rate. For example, in my case for my 50 year old decrepit body, (188-56) x 70% +56 = my target heart rate at 70% that is the equivalent of training at 70% VO2 max. Do the math, it is a significantly higher heartrate than simply 188 x 70%. As you increase the target percentage, the gap between methods becomes more narrow but even at 85 - 90 % you end up with meaningfully different results.

By the way, with respect to cardiac drift, ambient temperature plays a very large role. My daughter used me as a guinea pig for an 8th grade science project on the heart. Using a heart rate monitor, she recorded my heart rate over 6 months during once a week rides that were tightly controlled for variables of distance, route and average speed. In hot weather my avg H.R. on the ride was higher than in cool weather, demonstrating the effect of peripheral vascular dialation in the hot weather on core blood volume which then resulted in the cardiac drift. As she presented me with the results of her data and cautioned me about staying hydrated, I showed her an old Runners World article that touted beer as the perfect after exercise way to rehydrate and had a couple in the name of good science. :beer:

[Dr. Doofus]

The Doc didn't read this one until today, and everything posted by Needs and Too Tall is on the mark. Yeah, you see some Pros racing with HR monitor when it matters...but only because its the lightest-weight tool that provides some useful, although extremely limited and contextual, numbers. When they train, or when they gather race data, its with a watt meter...but more of that later....

HR monitors are, in the Doc's twisted opinion, next to worthless. The relationship of HR to power output isn't consistent, and HR is, as has been posted, subject to many environmental variables that make it a misleading gauge of effort. If you're racing, and your hobby is so important to you that you want to make the investment in training tools, then get a Power Tap, a Polar S720, or a used "sport model" SRM...anything else isn't really going to give strong data. "CP" -- critical power, or the sustainable average power an athlete can maintain over a given time duration, is a better training gauge...if you find you can average 170 watts, or 250 watts, or 200 watts, for a three-hour ride, then that's what you try and hold for the whole sucker...likewise, if race data says your CP for a 10mi TT is 350 watts, then do your LT intervals in that range.

The Doc, being a non-racer goofball who enjoys rolling around in his collection of stinky plastic Euro-poser jerseys (cause he always wanted them when he was younger but couldn't afford them, and since he's no longer racing real team jerseys have lost their joy for him, especially since all of his are nearly translucent, and because plain is boring...the Doc likes looking like a rolling blob of multicolored vomit as he advertises **** that isn't even sold in this country) now trains by the following easy-to-follow system of perceived effort, which is all he really needs. Your pleasure and results may vary, and don't try this at home.

Easy Ride: No trace of leg burn. Mind wanders. Rider starts to look for newspapers to throw. The Doc starts to wonder what the point of it is, then remembers that if he feels like he's actually riding, he's going to fast, and this is a rest day so back off, idiot.

Long Ride (2-4 hours): Moderate burn. Mind kind of wanders. But hurts just enough to feel like a good ride without actually breathing hard.

Tempo: Wow. Legs now burning a bit. If he didn't know better, he'd think this was hard, but no, he can keep this up for an hour or hour and a half, so its ok.

Long Interval: Lots of drooling involved. Now this hurts. Mind can't wander. Any faster and he and I would blow up and not make the interval. This is starting to suck.

Short Interval: This will all be ok as soon as I can put my eyes back in my head.

The Doc knows that perceived effort is not scientifically valid. So what. He's been riding since he was 14 (is now 37) and just doesn't care. Have fun. Also, in 1995 the Doc was in England ostensibly researching for his dissertation for two weeks, but he was really just getting away from his girlfriend, and anyway he was riding around the lovely southeast when he met his God, the guy who inspired him to place his levers where they are, one Mr. Y. During the 5 minutes of conversation before he excused himself, never to bother Mr. Y again, he noticed Mr. Y didn't have a HR monitor. The Man responded that after 14 years of being a pro, he knew his body pretty well, and only used it on easy rides to remind him to go slow...the rest of the time he held the highest speed he could for the interval....

I and the Doc kept playing with our toys for the next four years, but we've come back to that point. Ride, ride some more, enjoy it, get to know your body and how it responds to different intensities, and then ride by feel...its unscientific, but, in the words that echo through the head of anyone who has seen "Meatballs" (and not "Meatballs 2"...which sucked): "it just doesn't matter, it just doesn't matter."

[Too Tall]

Ken., I did a 10 mile TT 4 weeks ago and several recent races were at 342-447watts and am shooting for 350-360 by August. My 2X20s are done in the 330ish range (cause I'm a wuss). I'm 6'9" and 200lbs. I use an SRM Pro and cycling Peaks software for analysis. Uh, my racing results are coming along...not great...am still getting my fanny handed to me by guys who know how to race their bikes....but thanks.

I think my goals to get outta my former Ultra-distance mode and into racer boy mode would have been much more difficult without a watts meter and REALLY good software to work with. Thank g-d I have a good job to pay for this nonsense!

[Ken Lehner]

Ken., I did a 10 mile TT 4 weeks ago and several recent races were at 342-447watts and am shooting for 350-360 by August. My 2X20s are done in the 330ish range (cause I'm a wuss). I'm 6'9" and 200lbs. I use an SRM Pro and cycling Peaks software for analysis. Uh, my racing results are coming along...not great...am still getting my fanny handed to me by guys who know how to race their bikes....but thanks.

I think my goals to get outta my former Ultra-distance mode and into racer boy mode would have been much more difficult without a watts meter and REALLY good software to work with. Thank g-d I have a good job to pay for this nonsense!

I assume that those numbers include zeros, is that right? Perhaps I should give myself more credit because of my size (~77kg). I did the District TT yesterday (40K, of course) and averaged exactly 300W (3.9 W/kg), which compares favorably with your numbers. Of course, my best 2x20 ever (indoors) was only like 275W this winter.

Thanks for the information, and good luck with the racing!