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The Difference between Road and Mountain Bike Power Output and What Your Training Should Do About it. 
By Jason Hilimire 12.11.08                                                         Bookmark and Share 

Much is known about the power demands of road racing but little has been written for the lay public about the power demands of mountain bike racing. Below, I will show you the difference between road and mountain bike power. Then I will characterize mountain bike power and discuss how you can optimize your training to meet those demands.

Two 10 Minute Climbs at the same effort show two different power plots

To illustrate the difference between road and mountain bike power, I collected powertap power data on two different ten minute tempo climbs. The first climb was on a powertap equipped road bike up a steady 2-4 % grade hill. The second ten minute effort was on a powertap equipped mountain bike up a 10 minute singletrack climb also @ a 2 - 4 % grade. I rode both efforts at the same rate of perceived exertion (RPE) and had an average heart rate of 159bpm for both climbs.

In the graph below, I have overlaid the road and mountain bike power data on top of each other to visually see the difference in the two ten minute climbs. As you can see the power fluctuated much more from the mountain bike data compared to the road bike data. Average power for the mtb effort was 220 watts, while on the road it was 246 watts.


The main difference between the two files is the dramatic number of efforts above 300 watts for only a 220 watt average singletrack climb.

The road climb power has much more steady (even though it is variable) power without any forays above 300 watts.

Dissecting Mountain Bike Power Demands


From the power data we can see that this 10 minute singletrack climb contained 6 different sections where it was necessary to produce more than 300 watts.  These short burst like efforts lasted anywhere from 5 to 25 seconds (highlighted in purple below).   Short bursty efforts like these occur repeatedly during mountain biking, close to a hundred times during a 2 hour cross-country race.   I crossed checked a 2 hour mountain bike cross country race file and saw 88 such instances!


Mountain biking’s bursty power is primarily a function of terrain.   Rocks, roots, ruts, short steep climbs, switchbacks, obstacles and more all contribute to the highly variable power demands of mountain biking. It’s essential to mountain bike racing to be able to produce these efforts in order to clear the technical terrain and maintain your speed up, over, and thru the terrain.

Conversely, you’ll also notice that preceding most of these efforts are periods of zero wattage (highlighted in blue). This indicates that the terrain was fairly technical and I had to stop pedaling temporarily to clear a section of trail but then was back on “the gas”. When I started pedaling again I went from 0 to 300 watts to keep the momentum going. It’s these short burst efforts and the subsequent changes in wattage or cadence that truly distinguishes mountain bike racing from road racing. 
 
Cumulatively, these efforts add up to a big ‘ol physiological demand. Once or twice is nothing, but 88 times (like in a race) will absolutely bring you to stop.

If you reach that "capacity" in a race you’ll have no choice but to slow down.  However, if you work on raising your anaerobic capacity in training, you’ll have an extra gear to race faster. Much MUCH faster.

How to Raise your Anaerobic Capacity

In summary, mountain bike power is bursty as illustrated by the tempo climb above. Mountain bike power is even more bursty when racing flat out with your heart rate pegged at 180bpm. Therefore an athlete’s ability to perform zone 6 level efforts over and over during a mountain bike race is critical.  Having a huge aerobic engine is important too but having both is a lethal weapon.

At FasCat Coaching, we like to have mountain bike athletes perform Tempo Bursts Intervals. These structured intervals are performed at normal tempo wattage, but every 2-4 minutes, the athlete jumps up out of the saddle for 10-30 seconds at 125% or greater of their threshold power. After the burst, the athlete returns to their tempo pace/wattage until the next burst. Here is an example tempo burst workout:

·         Tempo Bursts: 3 x 9 minutes ON 9 minutes OFF b/w 224 – 266 watts w 10 seconds > 357 watts @ 3, 6, & 9 minutes

 As the athlete progresses, tempo can be replaced with Sweet Spot and even FULL GAS  Threshold work/wattages. Another example would be:

·         Sweet Spot Bursts: 4 x 10 minutes ON 10 minutes OFF b/w 245 – 286 watts w 15 seconds > 357 watts @ 2, 4, 6, 8
    &  10 minutes

The Sweet Spot Burst workout above is more advanced and much harder than the first tempo burst example. The most advanced workout is to perform bursts during a threshold interval. In other words, going harder when you are already going as hard as you can. 

·         Threshold Bursts: 2 x 20 min On 10 min OFF b/w 268 – 310 watts w 15 seconds > 357 watts @ 5, 10, 15, 20 minutes

As a side note this is an excellent workout for a time trialist racing over a variable and hilly course like the Tour of Missouri or jumping out of corners and accelerating on a course like the USPRO TT in Greenville this past year.
 
At FasCat, we reserve the Threshold Burst Intervals only for the 2 – 3 weeks pre-A race competition.   

These bursty intervals force the physiological adaptations required for the constant start/stop pedaling and short bursty anaerobic power that are necessary to ride fast over technical mountain bike terrain.

An Example Anaerobic Capacity Interval workout

Lastly, to work exclusively on your anaerobic capacity, there’s the old tried and true Zone 6 workout. Here is an example:

·         Zone 6: 2 sets of 4 x 1 min On 1 min OFF, Full Gas > 357 watts; 5 min inb/w sets

This workout contains 8 minutes (2 sets of 4 x 1 minute) of anaerobic capacity work. We adjust the total workload duration for the athlete on an individual basis between 5 and 25 minutes with never more than 7 intervals per set. 1 minute is a good middle of range anaerobic capacity duration but 30 – 90 seconds may also be used.

If you want to take your A game up to an A plus game this season on the mountain bike, these mountain bike specific intervals are just the ticket.

Copyright 2010, FasCat Coaching, LLC                                                    

Jason Hilimire is an Apprentice Coach with FasCat Coaching. He can be found out on the trails around Boulder, perfecting his short burst power.  To find out more about his coaching services, please contact him by email Jason@fascatcoaching.com

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