Mel McQuaid reviews the Powertap SL MTB Disc

As published on http://www.triathletemag.com

By Melanie McQuaid

April 22, 2008 — For the last many years that I have trained, first as a mountain bike athlete and more recently as an off-road triathlete, with about 80 percent of my riding hours on a road bike. This came naturally, as I have always done my interval training using a power meter and up until 2008, I did not use a power meter on my mountain bike. The time I used to spend riding trails focused more on quality endurance and technical training.

This winter I started to employ the Powertap SL MTB Disc off road. I have replaced one of my hill workouts with another off-road workout on hills and have started the process of data collection and analysis to compare my ability in January to my hopefully improving ability in April. What is interesting is a comparison of the hill workouts done on the road to my hill workouts done on the mountain bike. I have no doubt that some of my observations can help me to better plan for these workouts and tailor my training program to better reflect what I am going to encounter racing. Many of these observations merely confirm what we already know about the differences between mountain bike racing and road racing. However, the actual quantification of these differences is of interest.

For example, one trainer workout I did on the road bike was four to five minute intervals at 95 rpm and 85% of my maximum aerobic power. This workout is excellent for time trialing on the road and mountain biking, particularly in XTERRA, which really is a time trial. However, mountain biking is not as steady of an effort as a road time trial. So, the similar workout I did on the mountain bike was an uneven climb, at times very steep and at times almost level. My average was about 70 rpm for that climb at a much higher average power output than I would do on the trainer, particularly in the sections that were quite steep.

I think the trainer workout I was doing on my road bike would be great for long steady climbs at altitude, on a mountain bike, when you want to keep your heart rate under control. However, for mountain bike racing on rolling terrain, you will need to do intervals at much more than your maximum aerobic power, so a steady effort at 85% won’t cut it. Using a powertap to measure the average watts you can hold and the cadence you can maintain will help you gauge your improvements, whether by pedaling faster or by pedaling harder.

The other observation thus far has been that the average power output on a given mountain bike ride versus the average output for one of my road rides is much higher. This is obviously attributed to greater road resistance on fatter tires. It is true that after a mountain bike ride it may not feel like you have gone that hard because you are constantly distracted by the beauty of your surroundings, but the next day you are definitely more fatigued than you would be from a road ride. You also tend to maintain a much higher heart rate on the mountain bike without thinking about riding hard, which would give you better aerobic endurance gains if you incorporated off-road rides into your program throughout the winter. Less pain, more gain.

Although none of this is particularly new science, it is great to have a tool to help to quantify your efforts off road. It has been very useful for me to have the Powertap SL MTB Disc when I am doing intervals and now I can add greater specificity to my training by doing those intervals on my mountain bike. Training specific gets you fitter, faster and with the Powertap disc, filthy. Happy trails!

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Based in Victoria, Canada, Melanie McQuaid is a three-time XTERRA world champion. For more information about McQuaid, please visit www.melrad.com

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