Power vs speed and cadence

[Imtb]

Just started training with a power meter.

If I ride at average 270 Watts in a big gear for twenty minutes at 80% HR, will riding at a higher speed and cadence in slightly smaller gear but same power (270W) mean I am working harder during that interval - because my average heart rate might be at 88%

[Pilks]

Very interesting question ! thought i could answer but i dont know generally a higher heart does mean you working hard!

[Imtb]

But doesn't a higher wattage mean that you are working harder?

Let me rephrase that - I could be working at a higher power output but lower heart rate

Imtb2007-11-20 10:26:27

[Edition 507]

I can refer you to a good cycling coach if you are interested in him drawing you up a training program based on power

[Imtb]

I am already working with BikemaxPower but thought I'd throw the question to the forum Imtb2007-11-20 10:28:22

[Quicksilv3r]

Yea I would also think the higher your heart rate the better for training.

[Pilks]

Ya it does. I dont know hey wait for the likes of Bruce or bikemax to come on ! They can help you !

[Pilks]

This is an Efficiency question. Lower heart rate at the same output would indicate a good thing ! Means you can maintian that power for longer period. You heart rate basically tells you how fit you are ! if that make sense or is right then lucky me but i really know nothing mcuh about power about from matric physics

[Imtb]

Yea I would also think the higher your heart rate the better for training.

But you can work at a very high heart rate and spin all the way up a hill - at a slow pace and very little power 

[bruce]

This is a very interesting question!  The simple answer is that watts are a direct measure of exercise intensity.  HR is a response to that intensity.  Note that you should not be going faster at the same wattage.  All things being equal (gradient, wind, rolling resistance, etc) the number of watts you are producing dictates how fast you go.

The complicated answer has to do with muscle composition.  For a given wattage (270 in your case) the higher the cadence, the lower the torque because power is calculated from torque x angular velocity (cadence).  As torque increases, so your muscles will recruit more fast twitch fibres so the power is produced by a different combination of muscle fibres when cycling with big gears or small gears.  Now, depending on your particular muscle makeup, this may be better or worse for you.  Plenty of research has shown that your body is good at selecting the cadence/torque combination which suits it best which is why there is a move away from previously held beliefs that high cadence is always a good thing (ala Armstrong).

 

[Edit]  The recruitment of more slow twitch fibres places more strain on the cardiovascular system because these fibres are oxidative, i.e.  they operate aerobically - hence HR will rise.

bruce2007-11-20 10:38:03

[Quicksilv3r]

nyc Bruce!

[Imtb]

Okay I'm just trying to digest this - so if my interval is 20 minutes riding between 240 - 280 , riding in a really big gear to maintain that power is okay even if the speed is slower

[bruce]

The speed will not be slower - watts are directly related to speed.  Gear combo's are irrelevant. bruce2007-11-20 10:40:04

[Imtb]

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

 

Just the cadence will be slower?

Imtb2007-11-20 10:41:24

[Quicksilv3r]

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?

[bruce]

Yes, sure - which is why I said in my original post "all things being equal"

 

Power is the rate of doing work.  So if you are lifting a mass against gravity it is a much greater force than wind resistance, so your power output is high even though you are moving slowly.  However, on the same gradient, wind, rolling resistance, the more watts you produce the faster you go.