HR vs. Perceived effort changes during ride?

I've experience the same thing, and from what I've heard here it's pretty common. Changes in hydration from beginning to end of ride are the most likely cause for higher HR at the same or lower power levels.

I can be very well hydrated and still have cardiac drift, especially if it's hot outside like it has been. Just yesterday I did two 15 minute intervals with 10 min of easy spinning between them and 15 min of warmup prior. The first interval had a faster average speed and, although high due to the heat, my HR wasn't as high as on the second interval where my average speed was about 1.5 MPH slower. If I do two longer intervals (i.e. 2 x 15 or 2 x 20) my HR will ALWAYS be higher on the second effort than on the first, even though I'm faster on the first interval.

Also on steady state efforts my first half hour is always faster than even the second half hour if I train by HR alone. Even when I was doing steady 75% MaxHR efforts on the trainer the first hour is generally at least 0.2 MPH faster than the second hour and when I use the trainer I'll drink plenty of water before the ride, a quart during the first hour, 12 ounces during my break (always take a rest room break at 1 hour and grab a carb snack) and another quart during the second hour. On top of that I'll have a 20" box fan sitting right next to me aimed right at my torso on medium and I'll turn the air conditioning up just before getting on the bike. Nobody can tell me that I'm dehydrated when I drink that much fluid during a training session. It just can't be due to that. It HAS to be some other variable.

As for the perceived effort being easier toward the end of the ride, it is most likely due to being very warmed up by that time. Give this a try, jump on the bike with no warmup and average 85% MaxHR for a half hour ride. You'll be gasping for air. Then sometime when you're doing a 2.5 hour ride, start your HRM at the last 1/2 hour and average 85% MaxHR. It'll seem like a peice of cake by comparison.

All of these fluxuations in HR are probably why so many people ar training with power/watts. HR can be all over the place. A 90% HR on a hot humid day doesn't mean the same as it does when it's 70 degrees out.

jjjtttggg said:

I have noticed on several longer rides of about 2 to 2 1/2 hours (long for me anyway) that the perceived effort at a given heart rate is dramatically lower near the end of the ride than at the beginning.

For example, during shorter rides of about 1 hour, or in the earlier parts of my longer ride, on some of the hills around here my HR will rise to 172-175 (92% of MHR or so). It feels quite difficult and my breathing gets quite intense. I can maintain this level of output for maybe 5 minutes or so before I just have to gear down.

I travel a lot and one hotel I stay in frequently has an exercise bike with level settings in Watts. I get the same response (172-175bpm, high perceived effort, ragged breathing) on 3 x 5 minute intervals at 300W, with a 15 minute warmup and 5 minute recoveries at 200W. (Please note: I have no idea of the accuracy of the machine's power level settings.)

In contrast: near the end of my 2 hour ride I return by way of a long gradual climb at an average of 1% or so (steeper sections and a few dips, but mostly steady, gradual rise). My HR typically rises into that same 170+ range (maybe a couple of bpm lower), but my breathing is quite free, and my legs feel tired but don't burn like they do at the same HR earlier in the ride and I can maintain this state of affairs for about a 1/2 hour. I could probably go longer, but I arrive home after about 1/2 an hour.

Anyone have any idea what's happening? I don't have a power meter so I don't know whether I'm putting out as much at the end as at the beginning. Probably not, but why the high HR?

Thanks,
J

It's hard to say.sounds like your going pretty hard at it. it may be a hydration and or eating issue. or maybe your not recovered from your hard efforts. how often do you ride this hard? how much recovery are you giving your self? on the hills keep your hrt below threshold so you don't blow up. ride up at a pace you can maintain.

Doctor Morbius said:

Also on steady state efforts my first half hour is always faster than even the second half hour if I train by HR alone. Even when I was doing steady 75% MaxHR efforts on the trainer the first hour is generally at least 0.2 MPH faster than the second hour and when I use the trainer I'll drink plenty of water before the ride, a quart during the first hour, 12 ounces during my break (always take a rest room break at 1 hour and grab a carb snack) and another quart during the second hour. On top of that I'll have a 20" box fan sitting right next to me aimed right at my torso on medium and I'll turn the air conditioning up just before getting on the bike. Nobody can tell me that I'm dehydrated when I drink that much fluid during a training session. It just can't be due to that. It HAS to be some other variable.

Yep. My HR also seems to respond faster and stay at a high level more easily (ie, with lower power outputs) after one or more hard intervals. Maybe that's from being warmed up. I agree that there's more going on than just changes in hydration.

The funny thing is that my speeds gradually *increase* on the trainer when I'm maintaining a steady HR. I've alway attributed that to my magnetic resistance wheel heating up during the ride, and providing less resistance towards the end.

My HR also rises when I sit up and ride on the tops of the bars (compared to the drops), and maybe the OP is seeing some of that towards the end of the ride. From what I've read, sitting up straight or standing while riding raises the HR because more muscles become involved and start calling for greater blood supply.

frenchyge said:

My HR also rises when I sit up and ride on the tops of the bars (compared to the drops), and maybe the OP is seeing some of that towards the end of the ride. From what I've read, sitting up straight or standing while riding raises the HR because more muscles become involved and start calling for greater blood supply.

Or you increase wind resistance making you work harder to maintain velocity....

L

frenchyge said:

Yep. My HR also seems to respond faster and stay at a high level more easily (ie, with lower power outputs) after one or more hard intervals. Maybe that's from being warmed up. I agree that there's more going on than just changes in hydration.

The funny thing is that my speeds gradually *increase* on the trainer when I'm maintaining a steady HR. I've alway attributed that to my magnetic resistance wheel heating up during the ride, and providing less resistance towards the end.

My HR also rises when I sit up and ride on the tops of the bars (compared to the drops), and maybe the OP is seeing some of that towards the end of the ride. From what I've read, sitting up straight or standing while riding raises the HR because more muscles become involved and start calling for greater blood supply.

I have a fluid trainer so the resistance increases as the fluid heats up. About 3 minutes into the ride I can feel the resistance in the pedals kick in. I keep a small fan blowing accross the heat sinks of the unit to keep it cool and I point it upward a bit so that I can get some of the benefit as well. So I guess I have 2 fans plus extra air conditioning going when I'm inside using the trainer and I still sweat profusely! :eek:

I'd like to know what is causing so much cardiac drift ruling out hydration as being the main suspect. In my case a good portion of it is most likely attributed to my being a heavy person. A large person with less surface area for cooling will have more issues with core temperatures.

I have a question about the heart rate thing, at the end of a ride 85% seems like a breeze compared to the begining as stated. But how does that effect weight loss efforts? For instance it takes me about 15-20 minutes to get in my heart rate training zone at the begining of a ride, but towards the end of an hour ride or 2hour ride i am able to maintain that zone i.e. 70-80% with less effort. Is this good for weight loss? Does it benefit me or hinder me in my efforts to drop weight?

Lonnie Utah said:

Or you increase wind resistance making you work harder to maintain velocity....

Good point. I should've mentioned that I typically notice this on the trainer...🙂

Sublime99 said:

I have a question about the heart rate thing, at the end of a ride 85% seems like a breeze compared to the begining as stated. But how does that effect weight loss efforts? For instance it takes me about 15-20 minutes to get in my heart rate training zone at the begining of a ride, but towards the end of an hour ride or 2hour ride i am able to maintain that zone i.e. 70-80% with less effort. Is this good for weight loss? Does it benefit me or hinder me in my efforts to drop weight?

It's not HR that causes weight loss, it's the work being done by the body. HR is a tool (albeit an imprecise one) to help you determine the amount of work your body is doing. It's better than nothing, better than guessing, and better than monitoring speed, but not as good as directly measuring power output for the reasons that are being mentioned.

To answer your question, if your training plan calls for 1-hr of work at 85%, then ideally you should maintain that 85% level of effort/power for the whole period. If 85% feels hard at first, then you should maintain that hard feeling for the whole ride, even if your HR rises. If it feels like a breeze at the end, then you're doing less work even though your HR is still at 85%. In reality, though, weight loss doesn't require such precise training measurements to be successful, so HR is a perfectly suitable way to pace yourself and monitor your intensity. You should be using a HR range, rather than a specific bpm number, so maybe try to start low in the range, and finish high in the range.

Here are a couple of studies on cardiac drift. I haven't read them. Just found them referenced on another forum.

Coyle, E.F., and J. Gonzalez-Alonso. Cardiovascular drift during prolonged exercise: New Perspectives. Exer. Sports Sci. Rev. 29:86-92, 2001.

Dawson EA, Shave R, George K, Whyte G, Ball D, Gaze D, Collinson P. Cardiac drift during prolonged exercise with echocardiographic evidence of reduced diastolic function of the heart. Eur J Appl Physiol. 2005 Mar 12; [Epub ahead of print].

frenchyge said:

It's not HR that causes weight loss, it's the work being done by the body. HR is a tool (albeit an imprecise one) to help you determine the amount of work your body is doing. It's better than nothing, better than guessing, and better than monitoring speed, but not as good as directly measuring power output for the reasons that are being mentioned.

To answer your question, if your training plan calls for 1-hr of work at 85%, then ideally you should maintain that 85% level of effort/power for the whole period. If 85% feels hard at first, then you should maintain that hard feeling for the whole ride, even if your HR rises. If it feels like a breeze at the end, then you're doing less work even though your HR is still at 85%. In reality, though, weight loss doesn't require such precise training measurements to be successful, so HR is a perfectly suitable way to pace yourself and monitor your intensity. You should be using a HR range, rather than a specific bpm number, so maybe try to start low in the range, and finish high in the range.

He may not be riding with the same wattage over time, but his body is working pretty hard in an effort to cool itself down. So from a total caloric expendature perspective, 85% is probably 85% even though he's riding slower by the end of the ride. His heart doesn't know the difference and is still working very hard due to the body's efforts to keep cool. A good steam bath is a great way to burn calories without doing any exercise.