HEALTHAndFITNESS All ABout Power
take training to the next level with watts // By Ben Greenfield
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September 8th, 6 PM, Room 267
Deaconess Health & Education Building 910 W 5th Ave, Spokane, WA Bike mounted power meter. // photo ben greenfield.
While the training secrets of Tour de France cyclists have been suspect in recent years, one consistent performance-enhancing method is using a power meter. During the Tour, team coaches are carefully observing day-to-day variations in each cyclist’s power production, which gives valuable data on intensity, consistency, fatigue and peak performance. So why use power? Why not just glance at your inexpensive cyclocomputer? The problem with using speed to assess your intensity is that cycling is highly dependent on environmental variables, such as road or trail surface, drafting, and topography. Depending on the course, there can be significant differences between the efforts required to maintain speed on any given ride. Twenty-two miles per hour on the Centennial Trail from Coeur d’ Alene to Higgins Point will be far easier than the same speed up the side of Mt. Spokane! But wait—isn’t that the purpose of heart rate monitoring? While offering a better method of quantifying intensity, there are significant limitations to training with heart rate. Like velocity, heart rate is also dependent on uncontrollable variables like hydration, altitude, temperature, sleep and health status. Heart rate will also vary widely between individuals of different ages and fitness levels. Furthermore, heart rate has a “lagtime,” meaning that a very difficult pedaling effort may not fully affect your cardiovascular system until 30-60 seconds later, when it’s too late to adjust your intensity. Finally, heart rate does not measure your actual performance, but simply your cardiovascular response to any given effort, which means that even when you get fitter, you may not actually know if you’re getting any faster! Power (the amount of work performed during a given time) answers this quantification dilemma. With a power meter, the actual force and velocity of each pedal stroke can be directly measured, providing instant access to quantified data that’s simple to interpret and analyze, typically defined using the metric units of watts. Your power output determines not only your speed, but also the response of physiological variables such as heart rate and fuel utilization, so you get the best of both worlds. There are several power meters on the market. The SRM PowerMeter is the most expensive
($3000-5000) and is considered the gold-standard. It measures your power using strain gauges on the crank, with the output relayed to a handlebar-mounted computer. Powertap is another popular model, but measures power via strain gauges on your hub. While slightly less accurate, the Powertap is more affordable ($1000-2000) and a good option if you only use a single wheel set (you can’t switch the PowerMeter from hub to hub). At a similar price to the Powertap, the Ergomo is a relatively new brand to reach the local US market and also offers a crank-based measurement, but I’ve found bike compatibility to be an issue. Finally, less pricey models, such as iBike and Polar ($500-1000), use chain tension and chain speed to calculate power, but have highly variable accuracy. Once you’ve chosen a power meter and outfitted your bicycle accordingly, you’ll need to determine a few important baseline measurements to track your improvements. The most important and useful test I utilize with my athletes is the functional threshold power measurement, which is the average power produced during a 40-K time trial at maximum sustainable effort. For a less-fit cyclist who may have difficulty maintaining a hard effort for 50+ minutes, this test can be modified to be the average power produced during a series of shorter 15-20 minute efforts. Another important test is the peak power test, which measures maximum power produced in an all-out 30-60 second effort. There’s a highly useful series of in-depth articles at the website http://www.cyclingpeakssoftware.com/power411/. My recommendation for training with power is to begin with threshold and peak power testing, and then begin to ride with your power meter and track your numbers. You’ll have plenty of time for in-depth analysis as you learn more. Importantly, have fun and ride smart. // Ben Greenfield is a certified NSCA personal trainer, NSCA strength and conditioning coach, Serotta bicycle technician and ISSN Sports Nutritionist. He has authored multiple books on metabolism, nutrition and fitness and is an expert in holistic wellness management.
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DEACONESS HEALTH & EDUCATION BUILDING 910 W. FIFTH AVE., SUITE 510 (509) 747-1055
august 2008
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