I wrote a while back (in 2008) about how we all have different body types, and how our body type predisposes us to do well in some cycling events but not others. So many of us keep banging away at things we aren't suited for, because we don't know ourselves well.
This simplified graph shows how my best tested power ranks against the power of other cyclists. The higher my power profile bars rise in this graph the better I compare against those other cyclists in that length of interval in the four interval lengths at the bottom of it: 5 second, 1 minute, 5 minutes and 60 minutes). So, per the graph, my 5-second interval power is by far my best, relative to other cyclists. I'm not bad in the other intervals, but I won't win any races in them either.
The blue line shows my power as it was last year. The red line shows my power as it is this year. The biggest shift has been in my sprint power, which is sadly lower. But there's a tiny improvement in my 20-minute power (enlarge the image to see it!). You might think that very tiny improvement is not worth the big drop in sprint power, but it is important to consider this: My tiny 20-minute power gain is multiplied over a full hour of riding (I ride my L4s at my 1-hour power), while the sprint power is just subtracted from a few seconds. My total potential power is now significantly higher than before.
I know I did; trying to race my bike against real climbers in big, hilly road races and getting dropped almost every time. It took me many years to learn that I am, in fact, a sprinter. All that time I thought I was merely a slow, or undertrained at best, climber. It was a relief to finally understand what type of rider I actually was; one not meant to do well on big climbs! And it's taken me several more years to learn that I am not just a sprinter, but probably very close to a 100% pure sprinter. Well, 80% to be specific.
According to the experts extreme sprinter body-types have as much as 80% of their muscle fibers in the form of fast-twitch muscle fibers (usually called "type 2") and the other 20% in slow-twitch muscle fibers ("type 1"). Those extra fast-twitch fibers contract much more strongly than slow-twitch fibers, which makes sprinters so fast, but they also tire much, much faster. Don't I know that!
In the past my best guess, based on my feelings of how I compared with other cyclists, was that I was "about 60% fast-twitch, 40% slow-twitch." Why? Because I could climb fairly well, but sprint better. But I no longer feel that guess was right: I now think I am not only an extreme sprinter body-type, with close to 80% fast-twitch muscle fibers, but even more sprinter-skewed with a large portion of that 80% in the form of "type 2b" muscle fibers. Yikes!
Wait, I didn't explain what "type 2b" means. OK, the fast-twitch muscle fibers are further defined by "type 2a" and "type 2b" designations (and even "type 2x" which is sort of in between 2a and 2b). Both are fast-twitch but they have some differences too:
Type 2a muscle fibers
These are fast-twitch fibers ("middle distance"), but due to their construction they are also very trainable. In fact, they are so trainable they can literally morph from fast-twitch characteristics to become slow-twitch over time, with the right training. Type 2a fibers are red in color (as are type 1) because they have high levels of myoglobin and are thus more aerobic (oxygen burning). Dark meat!
These are fast-twitch fibers ("middle distance"), but due to their construction they are also very trainable. In fact, they are so trainable they can literally morph from fast-twitch characteristics to become slow-twitch over time, with the right training. Type 2a fibers are red in color (as are type 1) because they have high levels of myoglobin and are thus more aerobic (oxygen burning). Dark meat!
Type 2b muscle fibers
These also fast-twitch fibers (short distance), but rather set in their ways. They can only be trained to be stronger but never abandon their sprinter characteristics. I train these with "L7" jumps; short sprints at my absolute maximum possible power for about 6 to 10 seconds. Some people use weight training, but not I. Type 2b fibers are white in color and are anaerobic (no oxygen). White meat!
These also fast-twitch fibers (short distance), but rather set in their ways. They can only be trained to be stronger but never abandon their sprinter characteristics. I train these with "L7" jumps; short sprints at my absolute maximum possible power for about 6 to 10 seconds. Some people use weight training, but not I. Type 2b fibers are white in color and are anaerobic (no oxygen). White meat!
OK, back to me. How could I even begin to guess at my muscle-fiber composition without a muscle biopsy? Sure, cycling gives us chances to compare ourselves against other cyclists, but how reliable is that? Well, since I started training with a bike-mounted power meter I have had a whole new way of measuring and testing my performance versus others' performance: "Power profiling." I have been testing and logging my power from hundreds of intervals over almost two years now, and here's how my power profile compares against a huge number of other cyclists tested and entered into a big database:
This simplified graph shows how my best tested power ranks against the power of other cyclists. The higher my power profile bars rise in this graph the better I compare against those other cyclists in that length of interval in the four interval lengths at the bottom of it: 5 second, 1 minute, 5 minutes and 60 minutes). So, per the graph, my 5-second interval power is by far my best, relative to other cyclists. I'm not bad in the other intervals, but I won't win any races in them either.
In short, I'm a Ferrari. OK, maybe just a Honda S2000 (I am a small sprinter after all!). I have relatively lots of power at the "top end," but not much at the longer intervals. That's why my power profile slopes downward to the right; a strong endurance athlete with lots of type 1 muscle fibers would have a profile sloping upward to the right; they can't sprint to save their lives, but they can ride hard all day long. A generalist would have a fairly flat profile, perhaps with a bit of a drop at either end, reflecting their adaptability to varying conditions.
Unfortunately being a pure sprinter in cycling is a major drawback in most bike races. The best "sprinters" actually have a flatter ("general" or "all-around") power profile... though with a nice kick up on the left of that graph. They are fast enough in longer races that they can draft behind the type 1 endurance guys without getting dropped, then sprint around them for the win. I can sprint faster than those guys (in theory, all else being equal), but I usually get dropped long before the finish line so that doesn't help me much! In fact I've written about how my sprint power in an actual race is much lower than during my sprint training, even when I win, because the sprint always comes after a long desperate struggle for position at the front of the pack.
Now we all know that training is supposed to make us stronger, and it does. It also has this amazing capacity for changing our very physiology. I decided a few years ago to shift my physiology through training to make myself a different type of cyclist; a cyclist with better endurance, albeit at the expense of some of my sprint power. That can be done by training the type 2a fibers to act more like type 1 fibers. The type 2a fibers can literally be "recruited" to become more red... meaning they become more aerobic in function. Weird!
The training I've been prioritizing the last three years consists of lots of long "L4" (level 4) intervals. These L4s are simply intervals ridden at or near our aerobic threshhold for about 15 to 60 minutes. Painful but productive. I do about seven or eight 20-minute L4 intervals every week, year round. And it has worked as the graph below shows.
The blue line shows my power as it was last year. The red line shows my power as it is this year. The biggest shift has been in my sprint power, which is sadly lower. But there's a tiny improvement in my 20-minute power (enlarge the image to see it!). You might think that very tiny improvement is not worth the big drop in sprint power, but it is important to consider this: My tiny 20-minute power gain is multiplied over a full hour of riding (I ride my L4s at my 1-hour power), while the sprint power is just subtracted from a few seconds. My total potential power is now significantly higher than before.
All that hard training has changed my body type, and better equipped me to handle the aerobic demands of cycling. I am still not, and never will be, en endurance athlete... I'm still a sprinter who can get dropped, but it's less likely and I'll be fresher for the final sprint if I'm still there at the finish.
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Jesse