Heart Rate and Power, from a physiologist's viewpoint
 

Here is the first part of a two part article on the subject, by Ben Stone, of Sigma Human Performance, who works with my race team. He is a big believer in building up your ability to utilize fat.

http://www.sigmacoaching.com/using-p...rt-rate-vol-1/

cool article. i look forward to part 2.

interesting

Good read but having a power meter coupled w/ a HRM is the ultimate combo. I learned a lot about how my body was working with both of these working together. No way I would ever give up my pm. i trained 3 years w/ a hrm. thruth is that only a pm can show the gains or loses you make.

IMO, one measures both power and HR. I have attended lectures on what to eat and how to train to increase metabolic rate - burn more fat. However, the context was in long duration events such as RAAM. I can see the benefit for stage races as well.

What was left out of the power meter / HR discussion was the value of the power meter to limit wattage such as at the start of a time trial. HR lags and will be a bad indicator. Without power measurement one has to use level of effort and know when to believe HR.

I find constant power efforts more fatiguing than constant HR efforts. Let's pick something easy - z2 constant power. My HR will stay pretty stable over flat to rolling terrain and only drop when I am going slightly down hill for tens of seconds. On the other hand, power changes immediately if the grade changes. If I monitor 3 second average power and maintain z2 power my HR will be constant but it is a much harder workout with more fatigue than if I rely on HR. One can rely on HR IF one has calibrated legs and can hold constant level of effort as terrain changes. And I suspect many on this board will see a slight drop in HR if they let off the gas a little but this is IMO an individual thing.

My HR is affected by fatigue, hydration, amount of rest, amount of sleep and general well being.

I can see an argument for monitoring HR and using it as a tool along with other metrics such as power and quite frankly VAM. Remember, Team Sky, allegedly, improved at Tenerife by training with VAM but I also think they had a Belgian doctor with them.:D

AZT, thanks for sharing.

You're welcome.. :)

I use both, and certainly get value from both. As an example, right now I'm getting back into shape after an injury. My power is down. For awhile there was almost no correlation between power and HR, as my system was trashed. My HR would race >10 bpm more for a similar power output prior to the crash. That was certainly good info to have, and it helped to know when that went away and I started reacting more normally to efforts. Now that the systems are normal, and I'm just weak, the HR is a better guide the the PM for any extended effort. If I tried to maintain the power I had before, I'd blow up. I should probably do a FTP test, but that would be too damned depressing right now!

On the fat/carb thing, I agree that the ability to burn fat is of greatest value for TT and Tri efforts. That is born out by the fact that Ben's athletes do very well in those events. There is less benefit for those of us doing mostly crits, through I believe burning more fat at the lower efforts can't hurt. The issue is all the z2 time it takes to push that metabolic equivalency point up. Personally, when I've been in fat burning mode, I can really tell, and it feels good. No better way to take off weight, that's for sure. But winning races requires speed as well.

i've been in a similar situation with coming back from either non-bike related life events or injury that kept me off the bike for an extended period of time. first time was pre-powermeter. my HR was way, way higher than pre-time off the bike. like a hummingbird. but, i had no idea what that meant. coach said it was because i was rested, ok, well, it's june, how does that help me gauge where I was in April when i was building good form and how does it help me get fit/fast in the middle of my season? without the powermeter, the hr was just a random # and the only way to evaluate fitness was either by comparing to others or dropping $$ for VO2Max testing. This was the primary driver for me getting a pm and starting to train with it.

i havent worn a heart rate strap since, but that was 6 yrs and 2 categories ago. As i've gotten older (racing age 42 this year), i've struggled the past 2 seasons with keeping my weight down despite similar training and similar dietary habits. i've wondered if i should get the HR back into the equation to evaluate if my L2 efforts are equivalent to a "fat burning" zone.

If it's true that with the same calorie intake and energy expenditure, you've gained weight, the only conclusion is that your metabolic efficiency has changed. The only way to reduce weight now is to cut down on the number of calories consumed per unit work.

There is no such thing as a "fat burning zone;" fat is used as a substrate at all times. The proportion of fat consumed drops at high intensities, but at the same time, the total amount of fat used increases. None of this matters for weight control though as weight is determined through a simple energy balance and knowing arbitrary heart rate zone limits won't change that. If energy expenditure exceeds energy consumed, weight will drop regardless of how that was accomplished.

No, total oxidation decreases, not just the percentage of energy obtained from fat. If you go very hard almost no energy comes from fat.


http://www.ncbi.nlm.nih.gov/pubmed/11782653
The Fat(max) zone (range of intensities with fat oxidation rates within 10% of the peak rate) was located between 55 +/- 3 and 72 +/- 4%VO(2max). The contribution of fat oxidation to energy expenditure became negligible above 89 +/- 3%VO(2max) (92 +/- 1%HR(max)).


http://www.ncbi.nlm.nih.gov/pubmed/17062656

http://bikeforums.net/attachment.php...hmentid=303818

What about the "after-burner" effect, say after you do a set of vo2max workouts? If you are running a caloric deficit, would you be burning fat to provide energy? I would guess the fuel would be fat as you'll be at an exertion level why below the range for meaningful amount of glycolytic oxidation to take place

I've read the sometimes heated debates regarding whether how you get your calories matters in the weight loss equation, and, IMO, it does. Not all foods are processed in the same way, and there is variation in whether your body actually utilizes all the calories available from a given meal. It's not quite as simplistic a model as it is sometimes made out to be. And one of the reasons people refer to "fat-burning zones" is not only the higher percentage of fat that is being burned, but also the ability to maintain that level of effort for a greater duration, ultimately burning more totals calories, with many more of them from fat. Certainly worked for me when I was taking weight off. I became a "fat burning machine".

Yes, you burn fat at an increased rate after the intervals. High intensity exercise rapidly depletes glycogen stores and low glycogen levels shift your metabolism towards fat oxidation during the recovery period.

FATmax. Hmmmmm, who could we possibly pin that nickname on?

While weight gain/loss is certainly the result of a simple energy balance, that doesn't mean that you won't get better weight loss results working out in zones of different substrate ratios. The other variable is intake; if one style of hard work-out leaves you less inclined to "top the calories back up" than another, the former will be more conducive to losing weight. Compare two rides: ride 1 is a long steady ride in a slow-burn mode that burns, say 4000 kJ, half of which comes from fat; ride 2 is a more intense, shorter ride burning 3000 kJ, a third of which comes from fat. Both rides have consumed 2000 kJ in carbohydrates; they may produce a similar physiological response in terms of how much to eat before you're saturated, but the first ride burned 1000 kJ extra in fat.

I think both are good tools, but they're just tools. Don't expect them to push the pedals for you.

Interestingly enough, I'm finding my LTHR and Max HR has been dropping over the last year or even 6 months. Now I'm a bit of a special case due to my heart history. I used to be able to zing into the 190's relatively easily, but now it's 5-10 beats slower than that. I was told that after my surgery my heart would take a couple years and completely rebuild itself. That's apparently what has happened. I don't know if it's good or bad, but it's certainly an interesting thing to see happen. I'm riding strong and feeling good, so no problems there. Just so happens that my heart is slowing down. I'm curious where it's all going to settle in at.

geez man ... either one of those rides would leave me trashed and shell-shocked... anything over 2500 kjs and I am wiped out, lately.

Same here, but it depends how big you are. If you're 220#, the kJ's count up a little quicker.

I'm ~185, and 86 miles in my race Sunday showed just over 3000 kj.

To the more knowledgeable posters, what is going on when i experience a depressed hr at the end of a training block when i'm fatigued?

For reference, too well rested, hr equilibrates at 179 at the end of a evenly paced 30min ftp effort.
Well rested, this will be at 175, right where my lthr is.
Fatigued, this will be at 170.

One question i have is: does this mean that O2 uptake is different?

Hard-ass race.

I've always kind of assumed so. I think when you're really beat that you just aren't recruiting as much muscle fiber and so you don't use as much oxygen. That's just a complete guess, though.

Interesting read, thanks for posting. I see he is looking at power in a certain way. A way that I don't subscribe to though. He's looking at power over a short period of time (instantaneous or at least say 5 minutes) and that eventually the HR will catch up and give the true picture of what's going on in the body. I use my PM differently. What I want to know from my power is what am I doing right now relative to what I know I can do for a given period of time and my goals for the ride/race.

Like say my 15 minute climbing power is 300W. I know that if I hold 330W I (a) run the danger of blowing up on the hill (or TT course) and (b) my recovery period at the summit will be longer. If I run say 270W then the opposite is true plus (c) I know I have some reserves in case of an acceleration on the hill and (d) I'll have something at the summit where big guys like me can do something. Now maybe my HR will tell me whether I'm having a better or worse day than I had hoped and that my power assumptions are going to be wrong but I don't want to find that out 1/2 way up the hill. I want to perform as if my plan is accurate and make adjustments based on how I feel (pain and breathing).

My general philosophy is power is telling me what I'm doing right now and continuously throughout the ride. HR is telling me what the effects of what I did 5 minutes ago are having on my body.

Besides, if I'm doing 300W on a hill I already know where my HR is...high.

Ben certainly understands the use of power, and has his athletes utilize it for both training and during a race. He just feels the underlying physiology - what is happening with your heart - deserves more of a focus. So what I think he would say on the 15' HC is that if you get into the climb, and your HR is less than you know (from training and testing) you can handle for that duration, you should crank that power up a bit. You are having a good day. Take advantage of it. He would also point out that, if you exceed your HR limit for that duration, then you are going to blow up regardless of how much power you are producing. It's not the power output that blows you up, it's what that output requires from you physiologically.

He would also tell you to breathe like a drowning man coming up for air - another practice that many will debate.

Of course, Ben coaches (and does metabolic testing for) athletes where a PM isn't a convenient option, so it helps him to be able to coach using something fundamental and accessible like a HRM.

It's all good stuff to factor in...