Why does HR increase over time?

MaxPrime said:

I understand that it should, but what are the physiological reasons that the same level of output 50% through my ride is 75% of max HR and at 90% it's 90% of max HR?

Your heart rate is an indirect measure of exercise that is effected by blood volume, core temperature, hormonal response, fatigue, sleep, illness and level of fitness. Over the course of a single ride, blood volume/dehydration, temperature and recent illness are the biggest influences on the HR you see. Specifically, cardiac output (the amount of blood the heart is moving per minute) is the combination of beats per minute and how much blood is being pumped with every beat. However, the blood being pumped through your system is being used for more than the specific work of pedaling a bike. So as all of these variables slowly come more and more into play, your pulse rises more and more for a specific power output. Your best tool to counter this is proper hydration.

Smartt/RST said:

Your heart rate is an indirect measure of exercise that is effected by blood volume, core temperature, hormonal response, fatigue, sleep, illness and level of fitness. Over the course of a single ride, blood volume/dehydration, temperature and recent illness are the biggest influences on the HR you see. Specifically, cardiac output (the amount of blood the heart is moving per minute) is the combination of beats per minute and how much blood is being pumped with every beat. However, the blood being pumped through your system is being used for more than the specific work of pedaling a bike. So as all of these variables slowly come more and more into play, your pulse rises more and more for a specific power output. Your best tool to counter this is proper hydration.

Agree proper hydration is vital, as is skin cooling on a hot day. But I think there's something more causing the increase....perhaps something to do with endurance limits of the leg muscles?

My theory is that the muscle fibers get depleted and become less efficient as we continue on a long ride. Once the "easily accessed" fibers are fatigued, the C-V system has to provide more oxygen to more and deeper capillaries to recruit and employ fresh muscle cells.

This concept may be totally bogus of course! Comments?

dhk said:

Agree proper hydration is vital, as is skin cooling on a hot day. But I think there's something more causing the increase....perhaps something to do with endurance limits of the leg muscles?

My theory is that the muscle fibers get depleted and become less efficient as we continue on a long ride. Once the "easily accessed" fibers are fatigued, the C-V system has to provide more oxygen to more and deeper capillaries to recruit and employ fresh muscle cells.

This concept may be totally bogus of course! Comments?

There is a sense of truth to your theory, but not quite in the way you have stated.
Some muscle fibers will become depleted of their glycogen stores over time, while conjuctively, your body is making more fat available for energy by breaking down subcutaneous lipid stores. More oxygen is required to metabolize fat than carbohydrate, so therefore your pulse would increase with a shift from carbohydrate towards increased fat metabolism. However, this is imeasureable in comparison with the other influences I have stated.
If we're talking "endurance limits of the muscles" (which I assume to mean extensive glycogen depletion), then you will be at a point where you will not be able to cycle at a high enough power output to stimulate more than 65% of max HR: cardiac drift will no longer be an issue.

Smartt/RST said:

There is a sense of truth to your theory, but not quite in the way you have stated.
Some muscle fibers will become depleted of their glycogen stores over time, while conjuctively, your body is making more fat available for energy by breaking down subcutaneous lipid stores. More oxygen is required to metabolize fat than carbohydrate, so therefore your pulse would increase with a shift from carbohydrate towards increased fat metabolism. However, this is imeasureable in comparison with the other influences I have stated.
If we're talking "endurance limits of the muscles" (which I assume to mean extensive glycogen depletion), then you will be at a point where you will not be able to cycle at a high enough power output to stimulate more than 65% of max HR: cardiac drift will no longer be an issue.

What you have indicated here is quite interesting, and in some ways contradicts what "they" say as far as keeping HR's lower to burn more fat.

Frankly, I've never bought into that anyway. While I can understand, and believe that a higher percentage of fat is burned at lower heart rates, that only matters as far as the percentage goes. If you burn 1000 calories/hr. while 40% of it is fat calories, then you're burning 400 fat calories, or approximately 44 grams of fat. If you're burning 600 calories/hr. and 50% is fat calories, then you're burning ~33.5 grams of fat. Personally, I'd rather burn the 44 grams.

I realize my percentages may be off.. but I still believe it to hold true. I've burned almost 20 lbs. off in the past 2 months, and none of that (that I can tell) has been muscular weight. I try to exercise at just under LT most of the time, although my average generally falls well short of that.... usually around 140 BPM which is ~ 73% of my max HR. I'm currently at 190 lbs, and will probably go down to 180 eventually. I think I have too much upper body muscle mass to go much below that. 6' tall.

John

Mansmind said:

What you have indicated here is quite interesting, and in some ways contradicts what "they" say as far as keeping HR's lower to burn more fat.

Frankly, I've never bought into that anyway. While I can understand, and believe that a higher percentage of fat is burned at lower heart rates, that only matters as far as the percentage goes. If you burn 1000 calories/hr. while 40% of it is fat calories, then you're burning 400 fat calories, or approximately 44 grams of fat. If you're burning 600 calories/hr. and 50% is fat calories, then you're burning ~33.5 grams of fat. Personally, I'd rather burn the 44 grams.

I realize my percentages may be off.. but I still believe it to hold true. I've burned almost 20 lbs. off in the past 2 months, and none of that (that I can tell) has been muscular weight. I try to exercise at just under LT most of the time, although my average generally falls well short of that.... usually around 140 BPM which is ~ 73% of my max HR. I'm currently at 190 lbs, and will probably go down to 180 eventually. I think I have too much upper body muscle mass to go much below that. 6' tall.

John

Exercising at a "medium"/high endurance/just below 1hr power pace/or ~75% of VO2max is indeed the cornerstone of an effective weight loss program as it does have the best combination 3 key factors - a high rate of caloric expenditure (number of calories/hour) - a high percentage of those calories coming from fat - and it is not so intense that you can't sustain it for a long time in order to achieve a high total number of calories used.
The discussion of what it means to 'burn more fat' is often confusing when it is not clearly stated just what is meant by 'more'. But you seem to have grasped the general idea just fine.😉

Smartt/RST said:

Exercising at a "medium"/high endurance/just below 1hr power pace/or ~75% of VO2max is indeed the cornerstone of an effective weight loss program as it does have the best combination 3 key factors - a high rate of caloric expenditure (number of calories/hour) - a high percentage of those calories coming from fat - and it is not so intense that you can't sustain it for a long time in order to achieve a high total number of calories used.

The only problem being that out-of-shape people can't do CP60 on a daily basis without serious fear of injury or burnout.

If you're already fit, sure. If you're trying to lose weight as the first part of a "get-in-shape" program, it's my opinion you're better off with a lower intensity, in the interest of maintaining your ability to do the workouts consistently over several weeks or even months.

Smartt/RST said:

Exercising at a "medium"/high endurance/just below 1hr power pace/or ~75% of VO2max is indeed the cornerstone of an effective weight loss program as it does have the best combination 3 key factors - a high rate of caloric expenditure (number of calories/hour) - a high percentage of those calories coming from fat - and it is not so intense that you can't sustain it for a long time in order to achieve a high total number of calories used.
The discussion of what it means to 'burn more fat' is often confusing when it is not clearly stated just what is meant by 'more'. But you seem to have grasped the general idea just fine.😉

Well here's a question for you. I don't actually KNOW what my V02 max is, nor EXACTLY what my LT is..only by feel.

Yesterday I decided to push relatively hard to see what it felt like. The ride was 1 hour 12 minutes and my average HR was 158. That is ~83 % of my maximum heart rate. Is that high or low for a "race pace". I FELT like I could have pushed it harder still and actually expected my average to be much higher than 158 as I seemed to stay between 165-173 much of the time. Those down hills really bring the average down however.

What can I learn from this.....if anything. I CAN tell you that I've increased my average MPH over basically the same ride by over 5 mph in the past two months.

Thanks!

John

antoineg said:

The only problem being that out-of-shape people can't do CP60 on a daily basis without serious fear of injury or burnout.

If you're already fit, sure. If you're trying to lose weight as the first part of a "get-in-shape" program, it's my opinion you're better off with a lower intensity, in the interest of maintaining your ability to do the workouts consistently over several weeks or even months.

Personally I don't agree, I CERTAINLY wasn't in shape two months ago...at least aerobically.

What I found is that exercising at all kept my heart rate pretty high, even at the lowest intensity I could muster (lots of hills here). Over time, I've developed more control over that. I really haven't decreased the intensity as much as I've increased my distance and average speed. If I ride at the speeds I did in the beginning however, my heart rates are much lower.. MUCH lower...in the range of 125-135 BPM as opposed to 150-160.

Bottom line, if you're that out of shape, which I considered myself to be, it's extremely difficult to ride at lower rates. The first benefit you're going to see is to be able to ride at all.. which is hard enough in itself to increase your heart rates.

John

Mansmind said:

Well here's a question for you. I don't actually KNOW what my V02 max is, nor EXACTLY what my LT is..only by feel.

Yesterday I decided to push relatively hard to see what it felt like. The ride was 1 hour 12 minutes and my average HR was 158. That is ~83 % of my maximum heart rate. Is that high or low for a "race pace". I FELT like I could have pushed it harder still and actually expected my average to be much higher than 158 as I seemed to stay between 165-173 much of the time. Those down hills really bring the average down however.

What can I learn from this.....if anything. I CAN tell you that I've increased my average MPH over basically the same ride by over 5 mph in the past two months.

Thanks!

John

They're are several ways of determining your proper training zones, depending on the coach/exercise scientist you talk to. At RST, our zones are based on a ramped exercise test that is designed to take you to your maximum heart rate/aerobic power output. cyclecoach.comarticlesOpen ↗
If you max HR is indeed 190bpm, then your top end of sustainable heart rates, or "race pace", would be around 170 (what I think you have called your "LT"😉 and where your effort ended up.
I don't recommend the use of averages (eg: speed, HR) unless you can make the effort an uninterrupted one (i.e.: no significant decents, traffic lights, etc) for significant lengths of time.

Mansmind said:

Personally I don't agree, I CERTAINLY wasn't in shape two months ago...at least aerobically.

Interesting caveat -- in bold, above. What exactly do you mean when you say "at least aerobically"?

antoineg said:

Interesting caveat -- in bold, above. What exactly do you mean when you say "at least aerobically"?

I've done weight training off and on my whole life, so from a lean muscle standpoint, I have a descent amount of it. I don't body build persay, or at least I haven't since my college years, and haven't done much at all in the past 7-8 months.

I've just gotten to the point in my life when I don't particularly care to be "bigger", so when I'm participating in weight training...I usually stop when I start bulking up too much. I suppose because I've spent so much time doing it, I start to see gains fairly quickly.

That's a lot of the reason I've taken up cycling, I just wanted a different TYPE of exercise and... I just really enjoy riding. Also, I was approximately 210 lbs. at 6' which while I didn't look FAT, I certainly had more body fat than needed, and cycling has helped take it off (quickly too). I'm 37 and now can wear suits I purchased in my early 20's.

In any event, that's what I meant by the statement I made.

John

Smartt/RST said:

They're are several ways of determining your proper training zones, depending on the coach/exercise scientist you talk to. At RST, our zones are based on a ramped exercise test that is designed to take you to your maximum heart rate/aerobic power output. cyclecoach.comarticlesOpen ↗
If you max HR is indeed 190bpm, then your top end of sustainable heart rates, or "race pace", would be around 170 (what I think you have called your "LT"😉 and where your effort ended up.
I don't recommend the use of averages (eg: speed, HR) unless you can make the effort an uninterrupted one (i.e.: no significant decents, traffic lights, etc) for significant lengths of time.

The heart rate is based upon the maximum I've SEEN. I used the 220-age formula until I saw a heart rate obviously higher than that, so now I'm using the higher one. I saw this one on a particulary long hill that I attempted to hold 18 mph all the way up. I actually didn't see the 190 till I was slightly over the crest. I suspect it's a little higher still since from what I understand, I should have been "falling over" exhausted when reaching my max. I was definitely approaching that, but I didn't stop pedaling or anything.

I hear you on the averages, but lacking a power meter (will be getting the power unit addition for my Polar 720, it's the easiest way for me to see improvement (at least in numbers). That particular out and back trip is one I take on a periodic basis and is relatively consistent with respect to conditions. I suppose more than anything it's something to look at and make me feel good about what I'm accomplishing. 🙂 I realize it's hard to base anything on the averages, but it helps me establish some measure of the improvement I'm seeing.

Interesting really, I originally just wanted to bike to drop some body fat....and almost immediately I start analyzing everything I can measure in any way. You should see the spreadsheet I had set up until I got my Polar 720..lol. I'll send it if you want.

So from your post, I should be able to sustain an effort equal to 90% of my max HR for the duration of a race?

Thanks for the input,

John

Mansmind said:

I've done weight training off and on my whole life, so from a lean muscle standpoint, I have a descent amount of it. I don't body build persay, or at least I haven't since my college years, and haven't done much at all in the past 7-8 months.

I've just gotten to the point in my life when I don't particularly care to be "bigger", so when I'm participating in weight training...I usually stop when I start bulking up too much. I suppose because I've spent so much time doing it, I start to see gains fairly quickly.

That's a lot of the reason I've taken up cycling, I just wanted a different TYPE of exercise and... I just really enjoy riding. Also, I was approximately 210 lbs. at 6' which while I didn't look FAT, I certainly had more body fat than needed, and cycling has helped take it off (quickly too). I'm 37 and now can wear suits I purchased in my early 20's.

In any event, that's what I meant by the statement I made.

John

Hm -- I wouldn't have considered you "out of shape" then. Perhaps my statement was too vague. I should have said "people new to exercise". Even with cycling, which is a very low-stress sport, mechanically speaking, there is still a lot of tissue adaptation that takes place in the initial stages of fitness. The weight training background helps a lot with preparing the body for this type of adaptive stress.

As to your fitness, althought it may be true that you felt aerobically out of shape, the weight training also helps prepare you. Some of it is at the cardiorespiratory level, but a lot of it happens peripherally, at the muscular level. Muscular endurance, strength, and short-term power would not be limiters as you take up cycling.

antoineg said:

Hm -- I wouldn't have considered you "out of shape" then. Perhaps my statement was too vague. I should have said "people new to exercise". Even with cycling, which is a very low-stress sport, mechanically speaking, there is still a lot of tissue adaptation that takes place in the initial stages of fitness. The weight training background helps a lot with preparing the body for this type of adaptive stress.

As to your fitness, althought it may be true that you felt aerobically out of shape, the weight training also helps prepare you. Some of it is at the cardiorespiratory level, but a lot of it happens peripherally, at the muscular level. Muscular endurance, strength, and short-term power would not be limiters as you take up cycling.

I see your point. 🙂 I guess my "feeling" was based upon the amount of anger I felt at myself after almost dying trying to ride my first 6 miles on the bike.

Admittedly, my body adapted quickly... I did a 45 mile ride less than two weeks later (that was pretty stressful too).

John

Mansmind said:

The heart rate is based upon the maximum I've SEEN. I used the 220-age formula until I saw a heart rate obviously higher than that, so now I'm using the higher one. I saw this one on a particulary long hill that I attempted to hold 18 mph all the way up. I actually didn't see the 190 till I was slightly over the crest. I suspect it's a little higher still since from what I understand, I should have been "falling over" exhausted when reaching my max. I was definitely approaching that, but I didn't stop pedaling or anything.

I hear you on the averages, but lacking a power meter (will be getting the power unit addition for my Polar 720, it's the easiest way for me to see improvement (at least in numbers). That particular out and back trip is one I take on a periodic basis and is relatively consistent with respect to conditions. I suppose more than anything it's something to look at and make me feel good about what I'm accomplishing. 🙂 I realize it's hard to base anything on the averages, but it helps me establish some measure of the improvement I'm seeing.

Interesting really, I originally just wanted to bike to drop some body fat....and almost immediately I start analyzing everything I can measure in any way. You should see the spreadsheet I had set up until I got my Polar 720..lol. I'll send it if you want.

So from your post, I should be able to sustain an effort equal to 90% of my max HR for the duration of a race?

Thanks for the input,

John

90% is sustainable for ~60min, depending on motivation. 90% is sometimes called 'race pace' as it generally correlates with longer time trial efforts, the average you will see during a crit or on a long climb in a road race.

Mansmind said:

I see your point. 🙂 I guess my "feeling" was based upon the amount of anger I felt at myself after almost dying trying to ride my first 6 miles on the bike.

I know the anger well 🙂

Smartt/RST said:

Your heart rate is an indirect measure of exercise that is effected by blood volume, core temperature, hormonal response, fatigue, sleep, illness and level of fitness. Over the course of a single ride, blood volume/dehydration, temperature and recent illness are the biggest influences on the HR you see. Specifically, cardiac output (the amount of blood the heart is moving per minute) is the combination of beats per minute and how much blood is being pumped with every beat. However, the blood being pumped through your system is being used for more than the specific work of pedaling a bike. So as all of these variables slowly come more and more into play, your pulse rises more and more for a specific power output. Your best tool to counter this is proper hydration.

I'll drink like a fish and my HR still climbs during as little as a 1 hour ride. I even sit around and drink as much as 1/3 of a gallon of water before going out on a ride and my HR still goes up. Happens right around the 30 minute, 1 hour, and 2 hour marks. After the 3rd hour my HR will stabilize.

Doctor Morbius said:

I'll drink like a fish and my HR still climbs during as little as a 1 hour ride. I even sit around and drink as much as 1/3 of a gallon of water before going out on a ride and my HR still goes up. Happens right around the 30 minute, 1 hour, and 2 hour marks. After the 3rd hour my HR will stabilize.

The absolute quantity of blood plasma volume is not the only reason for cardiac drift. In fact it has more to do with the relative plasma volume, taking into account venous return and blood pooling. In addition, electrolyte losses or imbalances and muscular fatigue are factors.

I'd be curious if you had the same HR experience if you drank the equivalent fluid as electrolyte-replacement drinks (sodium, potassium, magnesium primarily) rather than just water.