Power vs Torque

June 4, 2009 · Comments

Torque is a measure of how much a force acting on an object causes that object to rotate.  Force per pedal stroke basically.   Power is a product of torque and rotational speed (i.e. cadence).

The power graphs below are a good visual example of the difference in torque and power and how it relates to the way you ride.

In the first graph (labeled “Torque”) I did a local climb at 60rpm in a big gear.  I averaged 369watts and 27 Nm of torque.  This is a great training exercise for building strength endurance.

In the second graph (labeled “Power”), I did the exact same climb and averaged 361 watts (nearly the same ave power). However, the main difference in how I rode this climb is I used a higher cadence of 80rpm.  This resulted in 11% less torque of nearly 24 Nm.  The speed was over 2.5km/hr faster in the second climb (even though the power was slightly lower) because I’ve lost about 5 or 6kg since.  Amazing how much of a difference a few kg’s will make when climbing.

Torque

torque

Power

power2

Greater torque and muscle tension is useful in training to increase strength.  In the beginning 3-4 weeks of a 12 week training block doing 2 x 20mins of these strength endurance (SE) intervals a couple times a week will have a great effect.    However, this isn’t good for racing as the added stress to the muscles cause damage and fatigue.  There’s an old adage, “save the legs, not your gears”  The biggest thing that you’ll notice when racing with the PROs is their very high cadence – especially in the first half of the race.  They are clearly saving the legs in anticipation for later.

Glycogen is stored in fast and slow twitch muscle fibers, with the vast majority in the slow twitch fibers. In other words, fast twitch power is extremely limited (fast twitch is what you’ll use when powering up a hill in a big gear). It makes strategic sense to use the slow twitch fibers as much as possible by spinning quickly up those hills and save that fast twitch muscle glycogen for when it’s really needed (i.e. when the winning move goes up the road).

  • The Big Ring
    Thanks Wade - have fun in Canada, I hear the maple syrup flows freely there and is delicious on just about everything you can eat ;-)
  • The Big Ring
    I am confused, looking at the screen shots you have posted.

    First climb lists interval data as 4.5 km, 16:33 = 16.31 km/hr
    Second climb says 6.22km, 19:36 = 18.96 km/hr

    Curiously, in both plots, your avg W/kg is listed as 4.5 - so even though you lost weight, your power / kg did not increase. I was under the impression that w/kg was the determinant for speed up a climb (as steep as Devil's Elbow at least) yet it would appear you certainly did go quicker.

    Finally,
    369W / 4.52 = 81.6kg
    361W / 4.51 = 80kg

    A loss of 1.6kg, not the 5 or 6 you mentioned...

    Publishing stats and power output online is tantamount to releasing trade secrets, Wade, have you posted those screenshots in an attempt to mislead your competitors? ;-)
  • Hey BigRing,

    Good eye...
    The thing that's misleading is that I don't update my weight in the powertap software. In both graphs my weight is constant and my power is almost constant. same pwr/weight. The main point of the graph was to show the difference in cadence and the power vs torque produced. I just commented that the reason I was going a couple km/hr faster was because I had lost some weight (which I'm quickly putting back on!).
  • Anonymous
    ECA but do your homework first! It still takes a balanced diet with plenty of small meals throughout the day and LOTS of water.
  • Tomo
    Tip Part 2:

    How to loose 5-6 kgs?
  • S
    Humans have a terrible thirst reaction. We wait too long before feeling thirsty and then when we do feel thirsty, we often mistae it for hunger. Sounds crazy huh?

    So, when you feel 'hungry' next, drink a glass of water and wait 2-3min instead. Then decide if you do need to eat.
  • Davo
    WKO+, trainingpeaks, only costs $100 usd as a one off.

    Well worth it...
  • me
    all interesting info.

    quick correction. either 24Nm is wrong or 22% is wrong. why? 22% of 27Nm is 5.94Nm. 27minus 5.9 is not 24. 11% less would be correct or 21Nm would be correct. or am i missing something? Good thing you ride good. ha ha.
  • oops...you're right. thx
  • Luke
    Hi,

    what program/software are the graphs plotted on?

    Cheers,

    Luke
  • powertap with the Poweragent software. WKO+ from trainingpeaks is supposed to be better but costs per year. Its able to tell some very important information with normative watts and intensity factor. Hopefully poweragent will be including this in their next release
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