Sunday, March 3, 2013

Chasing Dub

Chasing someone faster then you on a mountain bike, on some twisty singletracks, has to be one of the best mountain bike specific workout you can get. Whilst it is not structured and can ruin a perfectly planned day, it is the best workout a mtb racer can have because it makes you handle your bike at race speed, it requires the rider to hit different intensities and it forces you to pick good lines.

So I meet this guy named Dub, a master racer here in GA. We had a short chat and I decided to follow him on the singletracks. We did 2-3 full loops and it was an excellent workout. The guy was fast and smooth, handling the bike really well and staying off the brakes when it counted.

Overall, it was a good ride despite being a little more intense then what I had planned for the day. I should have tried to keep it steady Z2 but chasing Dub made it an entirely different workout. Came back home pretty fatigued and for some reason, my abdominals and lower back are totally shot, like if I had a massive abs workout at the gym.

Here are the ride stats. Lets analyze that ride with a specific XC mtb perspective.

Z2: 1h17min
Z3: 38min
Z5: 9min

Now lets have a more precise look at that power distribution.

Time spent between:
0-150W: 85min
300-400W: 22min
400-800W: 7min

I left everything between 150W and 300W out of the equation, you will understand why. I want to enlight a particular aspect of mtb riding and racing (given I chased Dub!). So what can we understand from the above stats?

First, I spent almost an hour and a half coasting and/or soft pedaling. That includes descents, corners where I couldn't pedal through and technical features I needed to overcome. That is a significant amount of time spent doing very little work you're thinking, and you're half right. Coasting on the trails, like mentionned above, is often forced by descents and technical features. During those segments, you pedal softly but your body is still working quite a lot. Indeed, handling the bike at speed, railing corners and maintaining traction all the way through requires some effort. This effort is not reported in the session kJ expendure. Therefore we could safely bet the session burnt more then 2800kJ. How much exactly? No way to know.

Second, lets add the two remaining ranges together, which would give us 29min spent between 300W and 800W. Nothing spectacular here, especially when you think a proper Z4 session would pile a mere 40min+ between 300W and 400W. Now the particularity of this specific distribution relies in efforts duration. Most, if not all of the time spent in that range is the result of multiple short, sharp efforts of less then approximately 15 seconds. What is even more interesting is those efforts were generally following a period of soft pedaling or coasting (see above).

That brings me to that specific mtb riding/racing aspect I wanted to talk about: the neuro-muscular (NM) demand of such bicycle riding. Suddently going from 50W to 350W or from 140W to 650W requires a very specific NM demand. The motor units recruitment, the firing patern and muscle contractions are very specific and different from, say, road riding. The kind of specificity you can't replicate on the trainer or on the road. Sharp accelerations out of corners, high intensity efforts to get over that steep little bump, muscle contractions required by clearing obstacles or constantly trying to be light on the saddle, lifting your butt arround to keep traction, etc. All those situations are what makes the NM demand of mtb riding/racing so specific. An aspect that shouldn't be neglected in a serious rider's training programme.

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