HR at different Cadences but same Power

Hurricane151

I noticed today during a roller session that my HR varies at different cadences but the same power. is this normal and does this suggest I have an "ideal" cadence.

For example with power maintained at zone 3.9 - 4.2 my HRs were as follows

90rpm = HR Zone 3.9
95rpm = HR Zone 3.7
100rpm = HR Zone 4.2

Any thoughts or is is just a natural varience?

Cheers

Trev The Rev

Hurricane151 wrote:

I noticed today during a roller session that my HR varies at different cadences but the same power. is this normal and does this suggest I have an "ideal" cadence.

For example with power maintained at zone 3.9 - 4.2 my HRs were as follows

90rpm = HR Zone 3.9
95rpm = HR Zone 3.7
100rpm = HR Zone 4.2

Any thoughts or is is just a natural varience?

Cheers

How are you measuring power? What do you mean by zone 3.9?

danowat

Yes, its normal, as for ideal cadence, not that old can o'worms again..........

Hurricane151

I am using a Powertap and I am using power zones (levels might be better) as follows

Zone 3 -Tempo = 76-90% FTP
Zone 4 - Lactate threshold = 91-105% FTP

GiantMike

I have seen a correlation (but not necessarily acausation) between lower cadence and lower HR for the same power output. I can't say that reducing cadence definitively reduces HR, but I think it does.

Here's an example of a workout with a strangely low HR compared to the previous day's attempt with the only real difference being reduced cadence.

I also find that waving my arms around (with a constant power and cadence) increases HR.

danowat

GiantMike wrote:

I can't say that reducing cadence definitively reduces HR, but I think it does.

I can, during cadence drills, my power is circa 150w, my HR is well into the realm's of what I'd expect to see at over 100w more than that.

I know it's an extreme case, but the increase in cadence taxes the cardiovascular system more than lower cadences do, HOWEVER......

It is the reverse at the other extreme end of the spectrum, during low gear work, I can easily see high HR's at low cadence.

I think there is an effecient range, where HR matches power, and outside of this, it does odd things.

MarkAshton

It makes sense.

Spin with zero resistance (i.e. chain not even attached) at 70 Rpm. Now spin with zero resistance and 100 Rpm.

HR will almost certainly increase at 100 Rpm.

I guess it depends on your muscle fibre type? Looking for an opinion here... but would it be safe to assume that slow twitchers generally prefer higher cadences (i.e. lower forces) compared with fast twitchers who prefer a slightly lower cadence (i.e. higher force).

For me, pushing a high force will tax the CV system less, but the legs quickly blow up. The opposite is also true, i.e. lower force/higher cadence taxes my CV more and legs can cope.

Trev The Rev

MarkAshton wrote:

It makes sense.

Spin with zero resistance (i.e. chain not even attached) at 70 Rpm. Now spin with zero resistance and 100 Rpm.

HR will almost certainly increase at 100 Rpm.

I guess it depends on your muscle fibre type? Looking for an opinion here... but would it be safe to assume that slow twitchers generally prefer higher cadences (i.e. lower forces) compared with fast twitchers who prefer a slightly lower cadence (i.e. higher force).

For me, pushing a high force will tax the CV system less, but the legs quickly blow up. The opposite is also true, i.e. lower force/higher cadence taxes my CV more and legs can cope.

I think most opinion is yes fast twitchers prefer more force lower cadence (for longer distances but not short distances on the track). But how many of us really know how much fast or slow twitch muscle fibres we have? It might just be that those who's cardiovascular system is stronger than their muscular system can tolerate the higher cadence better than they can the higher force? It might be more a preference for fast movement. Some people can move fast and find moving fast easy, others are slow movers but very strong. I'm not sure if this is related to muscle fibre type alone, perhaps it is (jumpers & throwers & sprinters = fast twitch but cycling is almost all low force endurance), but it might be more to do with neuromuscular pathways.

chrisaonabike

GiantMike wrote:

I have seen a correlation (but not necessarily acausation) between lower cadence and lower HR for the same power output. I can't say that reducing cadence definitively reduces HR, but I think it does.

The amount of power (consumed by the body, hence contributing to HR) required to drive the legs up and down will increase with cadence, since (among other things) you're lifting the upgoing leg aganst gravity. The more often you do that, the more energy you'll consume doing it.

So if power meters measure only the power driving the bike, it's not surprising if HR goes up with cadence, for a given power output.

Alex_Simmons/RST

Hurricane151 wrote:

Any thoughts or is is just a natural varience?

Pretty normal and of little consequence.

Trev The Rev

It is of no consequence whatever that an extremely high cadence uses far more energy to put the same power through the pedals. All that spinning like buggery uses masses of oxygen which does not get translated into measurable power, but it is of no importance whatever because the power meter does not measure your increased oxygen consumption. Cadence is a red herring. Wiggins was wasting his time lowering his cadence to convert a little more of the total oxygen he consumed into measurable power through the pedals. It really does not matter how hard you are breathing, how fast your heart is beating or how much oxygen you are burning, only the watts as measured count towards the power meter data.

Sit on your turbo, disengage the rear wheel, pedal at 100rpm with no resistance for 12 minutes and check your heart rate and breathing whilst generating zero watts. Don't worry about it burning all that oxygen is of no importance because it produced zero watts. It does not contribute to your training stress score. Forget it.

Tom Dean

Trev The Rev wrote:

Sit on your turbo, disengage the rear wheel, pedal at 100rpm with no resistance for 12 minutes and check your heart rate and breathing whilst generating zero watts. Don't worry about it burning all that oxygen is of no importance because it produced zero watts. It does not contribute to your training stress score. Forget it.

This would not produce zero watts FFS.

Trev The Rev

Tom Dean wrote:

Trev The Rev wrote:

Sit on your turbo, disengage the rear wheel, pedal at 100rpm with no resistance for 12 minutes and check your heart rate and breathing whilst generating zero watts. Don't worry about it burning all that oxygen is of no importance because it produced zero watts. It does not contribute to your training stress score. Forget it.

This would not produce zero watts FFS.

There being almost no force on the pedals an SRM would pick up almost zero power. You would be burning a lot of energy but very little could be measured as watts or as power put down through the rear wheel. I agree there might be a handful of watts, zero is a slight exaggeration.

You can get puffed out spinning pedals very fast with no chain attached. No chain no resistance no measurable power.

You would generate a lot of heat though pedaling at 110rpm without a chain. You could convert that to watts.

MarkAshton

Its clear a higher cadence will result in a higher HR for the same power.

People often say train at your natural cadence.... Thats a fair point i.e. the cadence where I can produce the most power for the chosen time period/distance.

The question becomes "Should we look to train at a lower cadence?" I personally like spinning at around 90-100 RPM. I shy away from anything less than 85 RPM (I personally find my legs tire quite quickly at anything less than 85 RPM). I often wonder if I were to train at 85 RPM (and thus increase my force), my body may adapt and thus allow me to produce more power for my chosen time/distance.

Tom Dean

Trev, it's not a situation that arises in cycling though is it? I can lift weight with my arms and burn energy, raise HR and guess what - zero watts on the SRM.

Trev The Rev

Tom Dean wrote:

Trev, it's not a situation that arises in cycling though is it? I can lift weight with my arms and burn energy, raise HR and guess what - zero watts on the SRM.

No, all I'm trying to point out in a sarcastic way is that 300 watts at 110rpm uses more energy than 300 watts at 85rpm.

e.g. you have to lift a foot 50 times more often per minute so a shoe & cleat alone at 0.25 kilos x 50 = 12.5 lilos per minute more to shift. Over an hour you have had to lift 750 kilos vertically 1038 meters assuming 73mm cranks just to shift a shoe. A power meter does not measure this work.

If only we could measure the total work done outside the lab and on the road in some way, like measure the oxygen used. As it is heart rate even though it is variable at least gives us a clue about total work done as opposed to only the power in watts as measured by a power meter. Heart rate is also not as variable as many would have us think particularly over longer efforts.

Working out the cadence range which gives you the most watts compared to total work is important. A heart rate monitor in conjunction with some form of power measurement can give you a very good idea. If you can hold 300 watts at 85rpm at a heart rate of 150 bpm but at 300 watts at 110rpm you are at 155bpm you have a clear indication. To say cadence is of no importance is power meter propaganda.

Wiggins claims Kerrison got him to drop his cadence a little. He didn't explain exactly why this improved his power very well though. But at Wiggins' power output only a tiny percentage is a few watts. Marginal gains and all that.

Tom Dean

But the goal is to produce more power, not to use less energy.

Trev The Rev

Tom Dean wrote:

But the goal is to produce more power, not to use less energy.

The goal is to sustain more power. So if a given power uses less energy at a certain cadence you should be able to sustain it longer and or sustain more power for the same energy.

danowat

Tom Dean wrote:

But the goal is to produce more power, not to use less energy.

Depends on what you are doing, events of sub 60mins (maybe 90?), I'd say yes, as much power as possible, events over that, you need to start thinking about effeciency too.....

Trev The Rev

danowat wrote:

Tom Dean wrote:

But the goal is to produce more power, not to use less energy.

Depends on what you are doing, events of sub 60mins (maybe 90?), I'd say yes, as much power as possible, events over that, you need to start thinking about effeciency too.....

Whatever the distance it is the highest power you can sustain for the duration. In a TT up to 25 miles you may well find that a less efficient cadence gives you the highest power you can sustain, but needlessly burning oxygen by excessive cadence is unlikely to get you your best time. In a TT you also have to take into account the highest power you can sustain in your TT position which might also impact on your cadence. In a road race saving energy is very important.

Cav rides at a high cadence in the bunch to save his legs for the sprint. This might not save energy but it does save his fast twitch muscle fibres. Yet many say cadence is of no importance.

Tom Dean

Trev The Rev wrote:

In a TT up to 25 miles you may well find that a less efficient cadence gives you the highest power you can sustain, but needlessly burning oxygen by excessive cadence is unlikely to get you your best time.

Huh? the highest power won't produce the best time?

danowat is right to say that efficiency has a bigger impact over longer distances. Improving efficiency is not a simple matter of changing cadence though.

Trev The Rev

Tom Dean wrote:

Trev The Rev wrote:

In a TT up to 25 miles you may well find that a less efficient cadence gives you the highest power you can sustain, but needlessly burning oxygen by excessive cadence is unlikely to get you your best time.

Huh? the highest power won't produce the best time?

danowat is right to say that efficiency has a bigger impact over longer distances. Improving efficiency is not a simple matter of changing cadence though.

To re phrase, the highest power you can sustain will get you the best time but you will not sustain your highest possible power or set your best time by needlessly burning more oxygen at an excessively high cadence.

Again I point to Wiggins decreasing his cadence slightly to improve his sustainable power.

The original poster asked about heart rate and rpm at a certain power. I would rather ride at the cadence that gives me the lowest heart rate for the highest sustainable power whatever that cadence might be.

danowat

I think you are starting to tie yourself in knots Trev.....

chrisaonabike

What is this 'efficiency' that people talk about?

Trev The Rev

danowat wrote:

I think you are starting to tie yourself in knots Trev.....

I'm saying that cadence is important and it is important to establish what cadence or cadence range works best for you. I'm also saying that power meters do not pick up the fact that at high cadences, less of your energy gets turned into watts that the power meter can measure.

MarkAshton

For TT's, If a lower cadence for the same power is more efficient, why don't people train to ride at the lowest possible cadence?

Trev The Rev

MarkAshton wrote:

For TT's, If a lower cadence for the same power is more efficient, why don't people train to ride at the lowest possible cadence?

If you go for too low a cadence you stress the muscles too much it is about balance. But why not train to produce your highest sustainable power at a cadence that does not waste so much energy?

Trev The Rev

MarkAshton wrote:

Its clear a higher cadence will result in a higher HR for the same power.

People often say train at your natural cadence.... Thats a fair point i.e. the cadence where I can produce the most power for the chosen time period/distance.

The question becomes "Should we look to train at a lower cadence?" I personally like spinning at around 90-100 RPM. I shy away from anything less than 85 RPM (I personally find my legs tire quite quickly at anything less than 85 RPM). I often wonder if I were to train at 85 RPM (and thus increase my force), my body may adapt and thus allow me to produce more power for my chosen time/distance.

I think this is what Wiggins claims to have done.

ut_och_cykla

Higher cadences tend to produce higher heart rates for the same output. Certainly for me anyway and I 've read it elsewhere too. But it may also be something you can train so you're heart doesn't have to work quite so hard. At very low cadences (50) the legs actually provide a pumping action to help return blood to the heart.

Alex_Simmons/RST

Trev The Rev wrote:

Tom Dean wrote:

But the goal is to produce more power, not to use less energy.

The goal is to sustain more power. So if a given power uses less energy at a certain cadence you should be able to sustain it longer and or sustain more power for the same energy.

You are confusing economy with performance.

Alex_Simmons/RST

Trev The Rev wrote:

The original poster asked about heart rate and rpm at a certain power. I would rather ride at the cadence that gives me the lowest heart rate for the highest sustainable power whatever that cadence might be.

I would rather they ride at a power level that elicits the desired adaptations and in a manner takes into account the specific event demands they are training for. HR has nothing to do with it.