I was having a discussion with one my off-road athletes this morning about the type of power required for mountain bike and cyclocross races. With her focus in these disciplines, we're working on not only bring up her steady-state power, but also her ability to repeatedly 'punch it' with hard anaerobic efforts and short recovery in between. The timing of this works out nicely because I have some fresh data from a race that really demonstrates what's required for success in off-road racing. Let's look at my power file from the Farmall Hill MTB race last night. This is a very fast local mountain bike race series in Rochester, NY. The course is like a twisty roller coaster with lots of short, steep, punchy climbs. For reference when looking at the graphs, I finished in 1:10 and my FTP is currently around 335 watts.
First, look at the cadence and power-zone charts. I spent 26% (18 minutes) of the race not even pedaling. Looking right to the power zone breakdown, notice that the vast majority of the time was spent in either Zone 1 (44%) or Zone 6 (33%). In fact, out of 70 minutes of racing, I only spent 16 minutes pedaling in Zones 2-5. Basically, I was either putting out almost no power or I was north of 400 watts (22 minutes).
Now, let's look at the graphs showing power throughout the race (only power and elevation shown for clarity). What jumps out right away is the complete "ON/OFF" nature of a punchy mountain bike race. Look how many times my power goes completely to zero only to go straight back up to Z6. What also jumps out in this view is the amount of efforts into the range of 750+ watts (200% of FTP or higher).
If we add some smoothing to the same file we start to see the length of the hard efforts come out a little more. A quick count using WKO shows around 35 efforts of 30 seconds each spent north of 400 watts (Z6). This doesn't include all the short 5-20 seconds bursts of much higher power. What also jumps out is how the recovery times between these efforts are very short, often even shorter than the efforts themselves.
If you're an offroad racer, think about the specific demands of these types of events. This needs to be replicated in training - not every day, but certainly in 1-2 key sessions per week. Think about short (10 second to 2 minute) bursts of maximal power with recovery in between. The length of the recovery can be tailored to the goal of the training. Shorter recovery creates a deficit that won't be cleared completely before the next interval, more similar to racing. This type of intervals also seems to have a significant benefit on steady state (think FTP) power production. Longer recovery allows higher outputs, potentially creating higher sprint power, but not necessarily benefiting steady-state power or high amounts of repeatability.
Some of my on-road athletes and triathletes will find that the idea of short, repeated, high power intervals sounds awfully familiar. That's because I've found it's a very time-efficient way to raise steady-state power and aerobic endurance. It also avoids doing a lot of long intervals at FTP power, which many athletes find mentally difficult and also tend create deep fatigue.
I hope this has provided some food for thought and helps dial in your training. Please feel free to contact me if you have questions or thoughts.