Power vs speed and cadence

[Quicksilv3r]

Oh make sense! thanks that explains allot! So more wattage = more speed in the same circumstances! Thanks bruce! Quicksilv3r2007-11-20 10:50:56

[bruce]

The speed will not be slower - watts are directly related to speed.  Gear combo's are irrelevant.

 

Just the cadence will be slower?

 

Power = torque (force) x angular velocity (cadence), so if you increase cadence, you must decrease torque (i.e. push an "easier" gear) to achieve the same power output.  Although the gear is easier per revolution, you have to do more of them, so you end up doing the same amount of work for a given time period and hence you are producing the same power output.  And vice versa of course.

 

I'll be back to this conversation in a short while - gotta put the kids to bed!

[Imtb]

Bruce along the same vein as Quicksilv3r. Speed will surely not always be the same at 270 W for an individual. If I drop down a gear but if I increase my cadence, perhaps get out of the saddle, won't I get back to 270 - is there no difference in speed. Sorry if I am sounding abit thick! 

[Imtb]

Yup, sorry gotta do some homework with the kids - be back later

[Racing Hart]

Bruce but if you are doing a climb wont your wattage be very high at low speeds? And if you on a flat wont you be going faster at the same wattage?

 

its basic physics..when going up i gradient you have a Y-component (vertically) of power pulling downwards(gravity) as well as a x-componen(horisontally) of power that  pulls backwards...so to have the same speed on a hill that you would have on a flat you have to put much more power on the pedals to get the same resultant power! speed is directy equidistant to power "fres = ma" / power = mass * accelaration..

 

Bruce along the same vein as Quicksilv3r. Speed will surely not always be the same at 270 W for an individual. If I drop down a gear but if I increase my cadence' date=' perhaps get out of the saddle, won't I get back to 270 - is there no difference in speed. Sorry if I am sounding abit thick! [/quote']

 

no as bruce said when shifting down you have a higher torque..so to have the same power the cadence has to be lower power = torque * cadence

Racing Hart2007-11-20 11:05:19

[bruce]

Bruce along the same vein as Quicksilv3r. Speed will surely not always be the same at 270 W for an individual. If I drop down a gear but if I increase my cadence' date=' perhaps get out of the saddle, won't I get back to 270 - is there no difference in speed. Sorry if I am sounding abit thick! [/quote']

 

No, not at all, this is actually quite a complex situation that we are discussing.

 

For a real disection, take a look at: http://swiss2.whosting.ch/mdetting/sports/cycling.html

 

In laymans terms, what this equation is saying is that the power that you are required to produce is to overcome:

Gravity

Rolling resistance

Wind resistance

Now, wind resistance is dependent on your drag coeffiecent, which is a function of your frontal area.  If you change your position, i.e. you stand up, you change your frontal area, hence your drag increases, hence you must produce more power to travel at the same speed you were when you were sitting.

 

 

[Quicksilv3r]

Yes and is it true that to double yor speed you have to put in 9 times the amount of power because air is 3 dimensions so it would be 2X2X2?

[bruce]

Yes and is it true that to double yor speed you have to put in 9 times the amount of power because air is 3 dimensions so it would be 2X2X2?

 

Yes, the speed vs. power curve is exponential, if wind resistance is the primary force you are overcoming.

 

Riding up a hill is a different story because gravity does not change with speed, hence speed increases linearly with power.

[Quicksilv3r]

yea ok makes sense so thats why aerodynamics plays such a large part in cycling.

[Imtb]

Thanks guys, I'm beginning to understand. So now to the training. I need to ride at 240 - 280 W for 20 minutes...do I need to pay attention to my heart rate ? Am I getting a better workout at a higher heart rate?

[Quicksilv3r]

Yea from what I know the higher the HR the better the workout. Let bruce answer he knows!

[Imtb]

  The simple answer is that watts are a direct measure of exercise intensity.  HR is a response to that intensity. 

I think you answered my question right there Bruce. So the higher the heart rate the higher the intensity of the training - which at the right time would result in quicker improvement on the bike. Is that right?

 

So could one say that in a race one wants the intensity at a lower heart rate but in order to achieve that one needs to train at a certain power at a higher heart rate so that the intensity of training is higher.

Threshold training...what % HR would be most beneficial 80% or 90% of max

Imtb2007-11-20 11:56:13

[bruce]

  The simple answer is that watts are a direct measure of exercise intensity.  HR is a response to that intensity. 

I think you answered my question right there Bruce. So the higher the heart rate the higher the intensity of the training - which at the right time would result in quicker improvement on the bike. Is that right?

 

So could one say that in a race one wants the intensity at a lower heart rate but in order to achieve that one needs to train at a certain power at a higher heart rate so that the intensity of training is higher.Not quite 

 

There are a couple of problems with this approach:

HR lags behind intensity, by up to a couple of minutes.  So for intensities around pVO2Max HR is too slow to give a good guide to the intensity you are performing at.

At lower intensities, HR is somewhat linearly related to intensity, but it is also impacted by hydration, fatigue levels, excitement levels, core body temperature, and other things.  So it is a guide but it is impacted by lot's of other things, not just intensity.

Above VO2Max, power is being produced by non-aerobic processes which do (by definition) not use oxygen and hence do not have the same effect on the heart.

The training effect is produced by progressive overload.  I.e. the body is subjected to incrementally more training dose, it responds to this dose, recovers to get stronger, and hence the dose can be increased.

Training dose = intensity x volume.  Now, since watts are a direct measure of intensity, the power you produce, for the time you produce it, is an exact measure of the training dose you have subjected your body to. By incrementally increasing this dose, positive training adaption occurs.

 

HR is not really required in this process, it is just an overall indicator of how your body is responding to the intensity, it is not a measure of the intensity.

[BikeMax]

 

  The simple answer is that watts are a direct measure of exercise intensity.  HR is a response to that intensity. 

I think you answered my question right there Bruce. So the higher the heart rate the higher the intensity of the training - which at the right time would result in quicker improvement on the bike. Is that right?

 

So could one say that in a race one wants the intensity at a lower heart rate but in order to achieve that one needs to train at a certain power at a higher heart rate so that the intensity of training is higher.

 

Threshold training...what % HR would be most beneficial 80% or 90% of max

 

No...

 

The measure of intensity is the power output (see Bruce's post) The HR is your response to that intensity. The HR response to a given intensity will be affected a many variables (fatigue, stress, hydration, nerves etc)

 

You cannot control your HR in training for a given power output Vs in training so better to forget about it and manage your intensity via the direct measure that you have at your disposal.

 

 

 

[Imtb]

Thanks Bruce and Peter, I understand what you are saying.

 

My threshold has been posted at 240 - 280 W but in my last training session someone mentioned this...

 

I have a feelling that the intensity for the L4 work may be slightly low ( based on your HR)
For the one session that you got pretty spot on in terms of power,  average HR was 158 for both intervals from what I can see ? so 83% of your max HR
You probably should be closer to 90% of Max HR

Would this indicate that my threshold could be higher?

Imtb2007-11-20 12:26:43

[bruce]

Thanks Bruce and Peter' date=' I understand what you are saying.

 

My threshold has been posted at 240 - 280 W but in my last training session someone mentioned this...

 

I have a feelling that the intensity for the L4 work may be slightly low ( based on your HR)
For the one session that you got pretty spot on in terms of power,  average HR was 158 for both intervals from what I can see ? so 83% of your max HR
You probably should be closer to 90% of Max HR

Would this indicate that my threshold should be higher?

[/quote']

 

No, it is just showing you that HR is highly variable, and as such is not the best metric to measure intensity.

 

Cumulative fatigue suppresses HR, meaning HR (for a given intensity/wattage) will decline over a period of intense training.

 

Threshold is the power you can produce for 1 hour, when you train at various percentages of threshold, HR will and does vary day to day, and even between morning and evening.

 

I regularly have to split up my interval training due to time constraints.  More often than not I'll have a greater than 5 bpm change in avg HR between the morning and evening.

 

Now if I was training according to HR, I would do one of two things:

not reach the required intensity because my HR is elevated.

Kill myself trying to get my HR up because it is suppressed.