Wattage Training and Polar S-720i Installation and Comparison


I finally sprung for a bike computer with wattage in addition to cadence and heart rate. It’s a Polar S-720i and I’ve finally gotten it to work. Here are some tips and what I’ve learned so far about training with wattage:
h4. Tips on using the Polar S-720i
After you follow the directions carefully, but it is a little flaky otherwise:
# “Sandiway Fong on S-710i installation”:http://external.nj.nec.com/homepages/sandiway/bike/feather/tt/s710/index.html. This applies to the S-720i too. Wish I had read this before I installed it.
# “Checking Polar installation”:http://mywebpage.netscape.com/rechung/wattage/testing/testprotocol.html. Here’s how to test the Polar to make sure installation is accurate. The main issue is that the chain speed sensor at the derailleur picks up interference. Main idea is move the chain speed sensor as close as possible to the chain. You also want the chain tension sensor as high as possible. It should actually hit the chain on the small-small gear combination.
# Ever so often the thing will go to zero across speed, cadence and wattage and beep twice. What has happened is that the watch is loose, there are two contacts on the back that have to be hard up against the bike mount. Jiggle the watch and it will slip in, beep twice and you are back in. I’ve found this happens no matter how tight the band is.
# When you start, you _must_ follow the watch to record correctly: a) wet the heart rate monitor belt thingy, b) push the red start button on the watch and you must _wait_ until you see a heart rate reading at the lower left (otherwise, heart rate won’t get recorded), c) push on the upper right button until you see the Trip odometer, d) hold the upper left button for 5 seconds to reset the trip meter otherwise, the distance won’t be right.
h4. Chris Carmichael on Power used in training
Why use Power Meters. Watching your wattage during the course of a ride is not very useful. Wattage fluctuates quickly and often; heartrate is a much better gauge of workload during a workout.
Power becomes useful when you are sitting in your living room after the workout. I recommend purchasing a power meter that can be downloaded to your home computer. Downloadable power meters help you see how your power output changes with your heartrate, speed, and cadence during the course of a single ride, a few weeks, or several months.
Increasing your sustainable power output at lactate threshold is very important for improving time trial performance. The intensity level for these workouts is critical. They must be done very close to an athlete’s lactate threshold heartrate, but not above that heartrate. You want to ride at the highest sustainable workload possible without accumulating lactic acid, which will force you to slow down. One way to keep the intensity high enough without overloading the muscles is to keep the cadence for lactate threshold workouts above 90 rpm. The higher cadence shifts some of the stress of the effort from the legs to the cardiovascular system.
h4. Power Meter Options
“Meinnovations on Power Meters for your Bike”:http://www.meinnovations.com/Power.htm. A good review of power meters here:
* “PowerTap”:http://www.graberproducts.com/category/category_control.asp?nextForm=fDetailCategory&originForm=fPrimaryCategory&id=94&action=delbc&killCache=true&navSection=cycle. Says that the PowerTap was the original and is accurate and a bit heavy at $600 street and one pound and you have to build up a special wheel since it is a hub, so you can’t just slap it on your bike. It is super accurate though
* “http://polarusa.com”:Polar S-720i. This is the newest device you can use on your bike enjoying your favorite scenery. It operates on chain tension and Polar’s very successful and popular wireless technology. Just as an electric guitar string generates a sound frequency, so does a bike chain. This is read by a sensor mounted to the chainstay and transmitted to the computer along with chain speed measured at the derailleur pulley and road speed measured at a wheel.
* “Comparing the Polar, Powertap and SRM”:http://mywebpage.netscape.com/rechung/wattage/rosetta/rosetta.html. A comparison of accuracy. Shows that they are about the same in accuracy. Whew, I’m glad I bought the cheapest smallest one. Amazing that this chainstay vibration thing works. Main issue is that the Polar doesn’t record wattages below 50-55 watts. Shouldn’t be a big issue. These are recorded as zeros, but the averages are correct.
h4. Training programs using power and wattage
_Hat tip to the meendurance.com site for these references_
* “Analytic Cycling’s Guide to Power”:http://www.pdqcleveland.org/power.htm. Has a PDF for a road cyclist guide to training with power. This is a great guide and well written that basically says, if affordable power meters came before heart rate monitors, they’d be the standard today because power is less subjective and variable.
* “Analytic Cycling”:http://www.pdqcleveland.org. Probably the nerdiest site in the world, so I love it. Really gets into the physics of cycling and how to improve. I could spend hours on it.
* “Robert Chang on Power”:http://mywebpage.netscape.com/rechung/wattage/. A great site with reviews of various meters and other things.

4 Replies to “Wattage Training and Polar S-720i Installation and Comparison”

  1. Very interesting article. This has really helped me make an intelligent purchase. Thank you..

  2. Glad it helped. It is a complicated topic. BTW, I love my Polar s-720i. Main issue has been learning the strnage quirks and getting it to do the IR transfer, but main thing I’ve learned is that an average wattage difference between 212 watts vs. 225 watts over a 10 mile difference can result in a 2 minute time difference. That’s huge.

  3. Where can i find info on elite athletes using power meters? What does a profesional cyclist average on a flat stage in a tour race? A climb? Which is the best power meter for the $?

  4. Good questions. Check out the Chris Carmichael links, he’s Lance’s trainer, so the answer is most use it for training.
    The typical professional biker can put out 500 watts sustained. The typical amateur more like 250 watts.
    In the current Tour de France, there is even a pro biker who haws his power meter on all the time since the bikes are now so light, you can afford to put them on (there is a weight lower limit on bikes of about 15 pounds and you can now build a stock bike at 14 pounds pretty easily).

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