[Fixed]

I did a test 10 mile time trial with an SRM. I found that my heart rate and perceived effort were pretty much constant, with BPM within 2-5 for the whole thing (except ramped up a bit in the last mile). However, my power dropped about 60 watts from about 3 miles until near the end, even though heart rate stayed the same during that time. What does that mean? What to work on? Thanks.

 

[shawndoggy]

flat course?

Did you go out too hard? That sorta sounds like the classic "drill it from the start then blow" scenario, where it still really hurts but your body can't put out the watts.

 

[Dwayne Barry]

It means there are factors beyond work rate than affect HR, which is why people have always said it is a relatively poor indicator of effort, calories burned, etc.

 

[Fixed]

flat

flat course?

Did you go out too hard? That sorta sounds like the classic "drill it from the start then blow" scenario, where it still really hurts but your body can't put out the watts.

Most flat, with a few rollers and turns.

I paced initially from what I thought my threshold power was, but apparently it has fallen, as I have been focusing on different (more long distance) training lately. But still, I'm just a bit confused by how much power can fall off for a given heart rate. That pretty much shows that pacing by heart rate is worthless (as mentioned below), or, I suppose, my threshold heart rate is really lower than I thought, too.

I always thought that if you started out at too high a heart rate, then sustainable heart rate would fall off as you go, along with power.

 

[CurbDestroyer]

Usually dehydration is the reason for power to drop at a consistant HR. I think chris Carmichael has a graph of this in one of his books.

 

[shawndoggy]

Most flat, with a few rollers and turns.

I paced initially from what I thought my threshold power was, but apparently it has fallen, as I have been focusing on different (more long distance) training lately. But still, I'm just a bit confused by how much power can fall off for a given heart rate. That pretty much shows that pacing by heart rate is worthless (as mentioned below), or, I suppose, my threshold heart rate is really lower than I thought, too.

I always thought that if you started out at too high a heart rate, then sustainable heart rate would fall off as you go, along with power.

But didn't you make this exact same observation from your analysis of your pine flat file (that power drops even though HR and RPE stay high)?

Seriously... try taking off the HRM for six weeks or so and see if you aren't getting better feedback from power. HR is just too hit and miss to drive your training (or at least your TT pacing). My bet is that once you abandon the HRM (or temporarily retire it) that you'll find it isn't missed.

 

[shawndoggy]

Usually dehydration is the reason for power to drop at a consistant HR. I think chris Carmichael has a graph of this in one of his books.

Dude it was a 10 mile TT -- I don't think dehydration is going to drop power by 20% in the course of 20 minutes.

Oh yeah, and carmichael is not the person to cite for power related issues. Just sayin.

 

[asgelle]

Usually dehydration is the reason for power to drop at a consistant HR. I think chris Carmichael has a graph of this in one of his books.

A far more likely cause is rise in body temperature, but cardiac drift is known to exist even under well cooled, fully hydrated conditions. It's a natural response to continued exertion.

 

[CurbDestroyer]

Dude it was a 10 mile TT -- I don't think dehydration is going to drop power by 20% in the course of 20 minutes.

Oh yeah, and carmichael is not the person to cite for power related issues. Just sayin.

I know it was 10 miles, but you assuming he was hydrated before the TT. for example a late night on the town complete with adult beverages.

Carmicheal has a graph that shows power drop in relation to percentage of water weight lost.I found it to be right on.

I have to find my power results from 60 mile ride I do that shows the drop in power to relationship HR. I did the ride a week late and hydrated better and it shows I was able to better maintain my power level at the end of my ride.

I know thats a 60 mile ride, but not all people prepare. I used to be one. After winning a 70 mile cat-1 road race one weekend, then to only then bonk after 30 miles the next weekend. My lack of preparation was the stuff of legend.

 

[CurbDestroyer]

A far more likely cause is rise in body temperature, but cardiac drift is known to exist even under well cooled, fully hydrated conditions. It's a natural response to continued exertion.

cardiac drift . . . that's what I was looking for.

 

[shawndoggy]

cardiac drift . . . that's what I was looking for.

But again, cardiac drift is the principle that over a long period the relationship between HR and power will decouple. Here we're talking about a massive discrepancy in a matter of minutes. While I don't disagree that hydration plays a role in HR and power, it's not the best answer for why a 20ish minute test went awry.

 

[CurbDestroyer]

The top set shows my melt down. The second is the next week and I get a couple more intervals in till my power fall 40 watts at the same HR.

 

[CurbDestroyer]

But again, cardiac drift is the principle that over a long period the relationship between HR and power will decouple. Here we're talking about a massive discrepancy in a matter of minutes. While I don't disagree that hydration plays a role in HR and power, it's not the best answer for why a 20ish minute test went awry.

The body is a funny thing. It is too short a time to put hydration as the sole reason. I think it is something to look at. And the next time he does a TT start hydrating a couple days before.

I'm just relating from the knuckle-head things I used to they to get away with before short races

 

[Mr. Bill]

My typical routine on the trainer includes going for X amount of time at X cadence in X gear - thus constant power output. My HR will drift upwards by some 5 BPM over an hour or so while doing this. Conversely, if I were to keep HR constant over that time I'd have to reduce cadence or gearing. Not any sort of expert in this sort of medical thing, but I suspect this is pretty much normal cardiac drift.

 

[asgelle]

But again, cardiac drift is the principle that over a long period the relationship between HR and power will decouple.

That implies there was a coupling in the first place. Cardiac drift merely refers to the observation that over time heart rate for a given workload increases during activity.

 

[Creakyknees]

I think you went out slightly above your actual "on the day" threshold, then couldn't hold it for the full length. HR and PE stayed high because you are effective at pushing thru pain.

Next time, try a reverse split in thirds - go out at maybe 250 for the first third, then maybe 265 then close out the last 3rd as fast as you can, 290 if you can do it.

I'm guessing on those numbers but you get the idea - go safely under threshold at first, try to be right at threshold in the middle (using PE, not power as your guide... feel your legs) then just do an interval for the last few minutes.

And leave the chest strap at home, just this once.

 

[iktome]

A bunch of things can cause cardiac drift, not just hydration.

But even ignoring those things, you'll almost always see some drift in a 20 minute effort. I find it takes at least 5 minutes for my HR to stabilize during steady, threshold power efforts. Even in shorter efforts, it still takes a significant percentage of the total interval time for HR to respond and stabilize.

If you were basing your effort purely on HR and RPE, you probably went out too hard to get the HR and RPE up to your target level. 20-minute (or similar length) intervals should always feel too easy at the beginning.

My RPE for a 20-minute interval is generally something like this (assuming a flat power curve, and averaging across the 2 or 3 intervals I'd do):
First 5 minutes: this is too easy.
Second 5 minutes: ok, this is starting to feel pretty hard.
Third 5 minutes: this really sucks and I'll never be able to finish.
Last 5 minutes: please get this over with. I usually try to focus on anything other than how I feel during this time. Generally I try counting pedal strokes.

 

[Fixed]

my typical time trial thoughts

First 5 minutes: this is too easy.
Second 5 minutes: ok, this is starting to feel pretty hard.
Third 5 minutes: this really sucks and I'll never be able to finish.
Last 5 minutes: please get this over with. I usually try to focus on anything other than how I feel during this time. Generally I try counting pedal strokes.

While I've pulled off just a few good time trials, more typically my thoughts are like this (not this last time, though):

First 5 minutes: Wow, 29 mph today. Feel good. Looks like a course record today.

Second 5 minutes: Hmm. Maybe that was a little too fast. I'll back off a little. Just try to stay over 25 mph.

Third 5 minutes: Why the hell am I going 20 mph? Must be a head wind. I think I could puke.

Fourth 5 minutes: God this hurts. Must be a head wind. If I can just average 24 mph, I'll be happy. Shift to bigger gear -- no that doesn't help. Shift to lower gear -- that doesn't work, either. What the hell was I think at the beginning?

 

[Alex_Simmons/RST]

I did a test 10 mile time trial with an SRM. I found that my heart rate and perceived effort were pretty much constant, with BPM within 2-5 for the whole thing (except ramped up a bit in the last mile). However, my power dropped about 60 watts from about 3 miles until near the end, even though heart rate stayed the same during that time. What does that mean? What to work on? Thanks.

Sounds like an entirely normal experience to me. Apart from improving your aerobic fitness, pacing is clearly something for you to work on.

Pacing a time trial with the strategy of maintaining a steady heart rate is poor pacing strategy (whether or not the strategy was intended). Power will almost certainly drop over time with such a strategy.

Here is a classic example of such a pacing mistake (heart rate, the red line can be seen here to be held fairly constant, while power fades consistently through the effort). This is from an attempt on the world hour record for a masters athlete:

Pacing a time trial with the strategy of maintaining a perceived exertion level is also most likely poor pacing strategy. Perceived exertion typically increases throughout such an effort.

 

[Fixed]

pacing goals and off days?

As someone mentioned, maybe some days are just off, resulting in bad pacing.

For example, a while back I was doing consistent time trial tests, both on the road and on the Computrainer. I found that my average power would be around 285 watts, even if I started higher and finished lower. However, the more closely I zeroed in on average power as I repeated the tests, the higher my average power actually became. So, I got faster.

Let's say I did this for a few months, and then my average power became 290 watts. On any given day, though, if I'm having an off day due to fatigue, dehydration, whatever, even if I start out with "perfect" pacing, anticipating 290 watts, if I can't sustain it, power will fall off and it looks like I went out too hard. That make sense? I assume that's what happened to the guy attempting an hour record, too. I'd think that by that time, the guy would know his power abilities, and would pace closely to what he *expected* average power to be, but simply could not pull it off that day. Therefore, it looks like he went out too hard and blew up. Could this actually be fairly common? Thanks.