Tuesday, 21 February 2012

Power Meters

History of Cycling Data Feedback
In 1983, Avocet launched the first electronic cycling computer which displayed speed and distance to the rider during a ride.  While pace is a great indicator of effort for running, it is more of a byproduct of cycling effort than an indicator of effort.  Wind resistance and terrain affect pace significantly, such that riding at 30KM/H can be done at either no effort or maximal effort depending on the conditions. 
We've come a long way, baby.
The first integrated cycling computer and heart rate monitor was launched by Polar in 1990.  Heart rate provided a more accurate measure of effort than pace, as it was a reactive measure of the stress put on the body by the cycling effort.  This reactive nature of heart rate feedback meant that heart rate was telling us the result of the strain we had just inflicted on our body in the past as opposed to measuring the current output of our efforts. 

Technology to measure the torque a rider applies to a bicycle whilst pedalling was developed during the 1980's, culminating in the launch of two power-measurement devices in 1989: the Power Pacer used by Team Strawberry in the 1989 Race Across America, which measured torque in a unit built into the hub of the rear wheel, and the crank-based power meter created by German company Schroberer Rad Messtechnik (SRM - literally translated as 'Schoberer's bike technical measurement') that was used by Greg LeMond during his 1989 Tour de France victory.  The Power Pacer eventually faded away, as the data was stored in the hub only to be retrieved after the ride was over, whereas the SRM data was displayed for the rider to see instantaneously.  

Power Meter Options
Despite the technology being launched two decades ago, it took many years for the price of these units to drop sufficiently to make them accessible to the every day cyclist.  There's currently three major manufacturers offering on-the-road power options:

1. SRM: The original and still the most popular choice amongst the pro peloton, also the priciest (around $2,700 to 3,700, depending on which crank you get it built on).  
2. Quarq: Another crank-based system, which comes in just under $2,000 from a company founded in 2006 and selling units since 2008.  The company was bought by SRAM in 2011.
3. PowerTap by Cycleops: PowerTap wheels have the power sensor built into the hub of the rear wheel, allowing for relatively easy swapping between bikes.  The cheapest of the three options, currently you can get a wheel for $1,000 new or as cheap as $400 for a used wheel.  

Garmin is currently working on a product called the Garmin Vector, which will be a pedal-based system, allowing for the easiest swapping between bikes.  June 2012 is the projected launch date and the pricing is looking like it will be somewhere between the PowerTap and the Quarq. 

Why Train with Power?
1. Power measures the work performed during a workout, whereas heart rate and perceived exertion measure your body's response to that work.  Check out the output from my workout this morning, with graphs for both HR and Power:


The goal for the 20 minute segment in the second half of the ride was to hold power around 335 watts for 20 minutes - you can see the power graph is relatively consistent over that 20 minutes, whereas heart rate over that same 20 minute period drifts consistently upwards, starting around 163 and rising to 180 by the end.  If the workout had been to hold 170BPM, the result would have been decreasing power output over the 20 minutes, in order to keep the HR consistent.

2. Being able to hit prescribed efforts in training regardless of conditions.  By recording your power output during workouts, you can establish a baseline level of fitness, and target specific power ranges in subsequent workouts to measure improvement over time and quantitatively measure the work performed in each session specifically, without having terrain, wind, or temperature affect the data.  300 watts of effort on a flat road with a tailwind is the same amount of work as 300 watts of effort going uphill into the wind.  Your speed in each of those scenarios will be vastly different, however, speed is simply an outcome of the power you create and the conditions under which the power is created.

3. Using a power meter won't make you a more 'powerful' cyclist on its own, but it could teach you to be a faster cyclist even on your first ride with power.  My first ride with power was a group ride, where in the peloton I was putting out 180 watts on the flats, then we'd hit a hill and despite my RPE increasing slightly, my power spiked to 400 watts.  I knew I was working 'harder' on the hills than on the flats, but didn't think I was working more than twice as hard.  Seeing my power during a ride allowed me to adjust the effort levels going up the hills and increase the effort in sections where I *thought* I was pushing hard, but found out the watts said I wasn't.  Watts don't lie. 

4. Pacing on race day.  Through training with a power, you develop a sense of what watts you're capable of maintaining over various distances.  This helps solve one of the toughest equations of long-course triathlon racing - how hard can I go on the bike without compromising my run?

The most common reason people don't train with power is that it's too expensive.  A friend of mine bought a used wired powertap for $400 on ebay, which is about the cost of a 70.3 race and two thirds the cost of an Ironman.  If you're committing the money and time to race long in 2012, you should consider putting a portion of your racing and training budget towards investing in power - your run split in your Ironman will thank you!


 

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