ProjectSSR- Part Three: Putting the Power to the Pedals
Posted: June 12th, 2008 by Lath CarlsonWith just one gear, the only other variables on a singlespeed are crankarm length and pedaling speed, or cadence. It turns out that there is more leeway in both of these factors then the convention cycling wisdom thought.
In an interesting study Jim Martin, Ph.D. of the University of Utah, and Waneen Spirduso, Ed.D of The University of Texas at Austin, found that crankarm length had little to do with maximum power output. They tested cranks from 120mm to 220mm in length at different power outputs and cadences. While the 145mm to 170mm cranks produced the greatest power (no 175 or 180mm cranks were tested), overall the differences were small. They also found that amount of energy each cyclist had to expend did not vary with either crankarm length, or with cadence. According to their research the perfect crankarm length would be either 20% of leg length or 41% of tibia length. For most people that’s a 160-185mm crankarm. Keep in mind, this study looked at maximum power, not sustained power, which I have not seen any studies of.
Does that look like 41%?
The situation when it comes to cadence is much less clearcut. Some early studies seemed to suggest that the optimal cadence was actually much lower than the 90-100rpm that cyclists typically ride, more like 50-60rpm. The limitation of these studies was that they were done with relatively untrained cyclists at low power outputs. More recent studies published in the Journal of Sports Medicine show that at higher power outputs, cadence has less effect. Researchers have also learned that the more trained the athlete is, the less effect higher cadence has. Since most racing takes place at higher power outputs, and with well trained athletes, cadence is not a big factor. This is actually good news for singlespeed riders. As long as you can keep your cadence above 50-60rpm having one gear should not be a disadvantage, until you are spinning so fast that you are not able to deliver power to the pedals. But, that’s a topic for latter when we talk about training. The biggest difference in cadence is what type of muscle fibers you are using at different speeds. At a lower cadence you are using more fast-twitch fibers, similar to sprinting, and at a higher cadence you are using more slow-twitch endurance fibers. Assuming that in a typical ride or race most geared bike riders try and keep spinning at the same rpm, they use mostly slow-twitch fibers. A singlespeed rider’s cadence is more affected by the terrain, and will likely spend more time in the high rpm and low rpm ranges. By spending more time in the low rpm ranges a singlespeed rider is using more of the fast-twitch fibers then the geared rider. There is a possibility that this more balanced use of the two muscle fiber types is an advantage.
Unfortunately, not enough studies have been done in this field for the results to be conclusive, although some of the more recent studies have had unexpected results. To me knowledge no studies have been done specifically on singlespeed vs. geared bikes. As always, the real testing is in actually riding and racing.
In the next installment we will look at the role training plays in getting the most out of you singlespeed.
June 12th, 2008 at 5:14 pm
Hold on, hold on! More fast-twitch (“sprinting”) fibers at low cadence?! I call factual BS. Fast twitch muscle fibers are just that, fast twitch, i.e. they contract more rapidly when a muscle group needs quick movement. This is exactly what’s happening when one is spinning a high cadence. High cadence cycling requires more rapid movement of the cranks through the pedaling cycle.
Slow twitch are the muscle fibers that are called for in lower cadences used when one pedals a tall gear, climbs, or is JRA.
Seems to me that the statements made here are opposite of the physiology I learned.
June 13th, 2008 at 10:16 am
I should have been more clear on that, here’s a source: “The explanation proposed here suggests the use of high rpms results in a decrease in average pedal force per revolution and leads to the recruitment of fewer fast-twitch fibers, placing the reliance for muscle power development primarily on the slow-twitch and intermediate fibers.” This is from a good article from: Cycling Science – Summer 1996 – What Determines The Optimal Cadence?. What seems to be of real interest here how when cadence and force demands on the body change, different muscular systems are recruited. When riding a geared bike most of us tend to keep our cadence and wattage within a fairly narrow range, while riding a single speed leads to wide swings in both cadence and wattage. With these swings the muscle types recruited seems to change as well as the cardiovascular demands. One theory is that these shifts from muscular endurance to cardiovascular endurance allow for periods of recovery for both of these systems between efforts. This would be most pronounced on a course with rolling hills.
June 13th, 2008 at 10:48 am
One more point of clarification regarding fast and slow-twitch muscle fibers. The names are a bit misleading, while fast-twitch fibers do contract more quickly then slow-twitch fibers that does not mean that they are directly correlated with the speed of the athlete’s movements. Fast -twitch fibers are used primarily for strength and power, for activities such as both weight lifting and sprinting. Slow-twitch fiber are used primarily for low intensity and high endurance efforts, such as distance running. Just because a low rpm, high power, climbing effort is done at a relatively low cadence does not mean that it is not primarily using fast and intermediate twitch fibers.