Technical FAQ: Essential tremors, 1X vs. 2X, and fast- vs. slow-twitch muscle fibers
I would like some assistance in selecting the specifications for a stable bike, or an outright bike recommendation. I am 70 years old, 170 pounds, and 5’11”. I ride about 200 miles per week. I have a medical problem called essential tremors which causes me to shake sometimes. This can cause speed wobbles while descending. And it scares other riders in a pace line. Neither situation is good.
I have a 2002 custom titanium Serotta with a wheel base of 99.7 centimeters and a head-tube angle of 73 degrees. Also, I own a Trek Domane 4.5 (58cm) with a wheelbase of 102.2 centimeters and a head-tube angle of 73 degrees. Both of these bikes have a tendency to wobble, the Serotta more so than the Domane.
We (meaning we at Zinn Cycles) deal with shimmy caused by essential tremors the same way we deal with shimmy due to a rider being tall and heavy, with the notable addition of a steering damper. As I discussed in four past columns, from May 2002, October 2013, November 2013, and July 2014, the main solution to shimmy is for the bike to be super stiff — both the frame and the wheels.
We recently built a bike for a customer with exactly your issue. He is similar in size to you — 6’0” and 176 pounds — and had a number of bikes, all carbon, I believe, and all of them shimmied due to his essential tremors. Like you, he found it unnerving on descents, and riding companions found it unnerving on group rides. We built him a rock-solid, super-stiff steel frame with oversized tubing that he said, “lived up to [his] expectations.” He reported that the bike (without the steering damper — see below), “doesn’t respond at all to my unintended inputs, it just goes straight down the road. It is super stiff torsionally, as advertised. I can’t twist it at all, which is a big change from anything else I’ve ever ridden.”
For further security from shimmy problems, we installed a steering damper inside his steering tube. This damper cannot be installed in most carbon forks because, to secure it inside of the steering tube, you have to be able to get a 12mm socket on the end of an extension up inside the steering tube from the bottom, and most carbon forks have no hole under the fork crown up into the steering tube. For this reason, we resorted to a WoundUp Road X carbon fork with a tapered steering tube and a fat, aluminum crown; it has a hole in the bottom of the crown large enough to allow the 12mm socket to pass.
The damper is adjustable with a knob on top, and it can be set so that the fork rotates quite freely, or set so that it is so heavily damped that it takes a firm push to turn the handlebar. This greatly reduces any wag coming from the hands into the bike. An extreme version of the damper’s effect can be seen in this video of a mountain-bike rider who does fast, technical riding with one arm.
The data plot power losses in the Gear Issue article “Friction differences between 1X and 2X drivetrains” is totally unreadable due to its small size. Is there a higher resolution version of that somewhere?
Well, one way to be able to read the sizes of the chainring and cogs inside the little circles on the graph is to get it in print. You can read the gear sizes inside the little circles on the printed page. I’ve also included a higher-res detail below (click it to enlarge).
In cycling, something very interesting happens that nobody talks about (at least from what I’ve read or seen). We have fast-twitch (FT) muscle fibers, and we have slow-twitch (ST) muscle fibers. FT fibers do the hard and fast work (anaerobic system in action), while ST fibers do the easy and slow work (aerobic system in action). Well, in cycling, we have gears, which means for a given power we can have higher cadence along with lower force, and we can have lower cadence along with higher force. Therefore, in this cycling context, something is totally different: we have FAST along with EASY, and we have SLOW along with HARD. Do you see the difference as I see it?
In running (or other similar activities) you don’t find this situation. Instead, you have fast along with hard, and you have slow along with easy. So, what’s going on with cycling? When doing low-cadence-high-force, which muscle fibers work most? Do the ST fibers cause low cadence? Or do the FT fibers cause high force? When doing high-cadence-low-force, which muscle fibers work most? Do the FT fibers cause high cadence? Or do the ST fibers cause low force?
Any idea about this unique aspect of cycling?
― Mircea from Bucharest, Romania
Here’s the answer to your question from long-time cycling coach, elite racer, and VeloNews physiology and nutrition contributor and Fast Talk podcast co-host, Coach Trevor Connor:
This is a really good question. I actually wondered the same thing a few years ago and researched the question for a bit.
Here are a couple things that really helped me to understand the issue. First, fast- and slow-twitch are a bit of a misnomer. Yes, fast-twitch fibers are capable of contracting a little faster than slow-twitch fibers. That was one of the first differences researchers discovered between fiber types over 100 years ago, hence their names. But over the years it was discovered that that was not the major differentiator between the fiber types. The more important differentiator is the way in which they use fuel: some fibers have the ability to use aerobic metabolism/burn fat while others rely on glycogen as fuel. So, a lot of researchers now refer to the different fibers as type I oxidative, type II oxidative, and type II glycolytic fibers. (There are two major types of fast-twitch or type II fibers.) The second important thing to understand is that in cycling, unless you pedal at a really high cadence, you’re never pedaling fast enough for it to be too fast for “slow-twitch fibers.”
The more important thing to remember is what’s called the “recruitment principle” in physiology. When a muscle contracts, it almost never uses all of its fibers. It only recruits enough to perform the given work. So, for example, if you curl a 30-pound weight, your bicep might recruit 100 fibers, while if you pick up a pencil it may only recruit 10 fibers. The recruitment principle says that we will always recruit our slow/oxidative fibers first. Once the muscle has recruited all of those fibers, it will start recruiting the fast-twitch fibers.
So, in cycling, the number of fibers we recruit depends on the torque. The higher the torque, the more we recruit. As strange as it sounds, when you do low-cadence work, you’re producing higher torque per rotation, so you’ll need to recruit more fibers to turn the pedals, and you will actually recruit more fast-twitch fibers than you would when pedaling at the same wattage but at a higher cadence. This is one of the reasons pros practice riding at a higher cadence. Our slow-twitch fibers don’t really fatigue, so if you pedal at high cadences, you can produce higher wattages without producing a lot of fatigue.
On the flip side, it has been shown that doing low-cadence intervals strengthens slow-twitch fibers and allows them to do more work before you start recruiting fast-twitch fibers.