Feeling Twitchy? The Difference Between Fast and Slow Twitch Muscle Fibers

A topic that's interested me since taking up cycling several years ago has to do with the muscles used in different sports, and more interestingly, how the very same muscles can be used quite differently. Prior to rediscovering cycling I was a pretty serious soccer player, playing on my college team and continuing at a competitive level after college and graduate school.

After my first year back on the bike -- having started a regular commuting regimen along with longer weekend rides -- I noticed an interesting impact on my performance on the soccer field. On the one hand, I was in better cardiovascular shape than ever and my weight was down (about 20 pounds from the year before and even 10 pounds below my college soccer days). I typically play in center midfield, a position that involves the most running in a sport where you’re constantly moving. Now I felt like I could run forever; like I could play two 90-minute games back to back!

The problem was I felt like I had lost my quickness. My first step seemed slow, and I was getting beat by feints I would have stopped a year earlier (even when I was carrying 20 pounds of extra girth).

What was happening?

A friend of mine suggested I add some short sprints and jumping to my training, and when I did a little research to find some drills I found he was right. Apparently my cycling had done an excellent job developing slow-twitch muscle fibers, whereas soccer demands both slow and fast-twitch fibers.

What’s the difference?

Physiologists now believe that muscle fiber types can be broken down into two categories: slow twitch (Type I) muscle fibers and fast twitch (Type II) muscle fibers.

So what?

These distinctions apparently influence how muscles respond to physical activity, with each fiber type capable of contracting in a certain way. Slow Twitch (Type I) are very efficient at using oxygen for continuous and extended muscle contractions over long periods of time. They fire more slowly than fast twitch fibers and take longer to fatigue. These fibers are great for cycling for hour after hour or for running a marathon.

Fast Twitch (Type II) fibers operate anaerobically (without oxygen) to supply short bursts of strength or speed. Think of weight lifters. They don’t typically breathe hard (at least not for long) because the muscles they’re using (1) don’t require much oxygen, (2) fire quickly and are (3) are done doing their work sooner. Fast twitch fibers produce the same amount of force as slow muscles for each contraction, but they fatigue more quickly. Having more fast twitch fibers can be an asset to a sprinter since she needs to quickly generate a lot of force.

But there’s another interesting wrinkle.

Physiologists suggest that human muscles possess a genetically determined mixture of both slow and fast fiber types (around 50% of each). One important question that apparently has not been definitively answered is “can training help an athlete change the fiber type and composition of their muscles?”

There is an interesting sub-class of fast twitch muscles often referred to as Type IIa, also known as intermediate fast-twitch fibers. They can apparently use both aerobic and anaerobic methods to create energy. In this way, they are a combination of Type I and Type II muscle fibers. So, theoretically, an endurance athlete can "recruit" these dual purpose fibers to act more like slow twitch muscles, while a sprinter can use them for fast twitch power and speed.

It's interesting to think about how these types of muscle fibers affect cycling performance at the highest levels. Great all-around cyclists (and team leaders) need to be able to do everything reasonably well -- climb, sprint and endure mile after mile in long multi-stage races. They need both slow and fast-twitch muscles. But the very best sprinters (those who specialize in the last 100 meters of the race) must have explosive power, and therefore well-developed fast twitch muscles. You can see this directly in their body types. Sprinters are often "bulkier" than generalists, who tend to be lean and sinewy looking.

In the end, although training may or may not actually change the fiber type from slow to fast twitch (or vice versa) it’s clear that it does help you more fully realize the potential your muscles have for work (either intense bursts of power and speed, or long, grueling periods of activity).

Plastics Scare a Sign of Deeper Regulatory Problems

If you've been following health news recently you know that Health Canada (the Canadian health agency) is preparing to declare the chemical bisphenol-a, or BPA, toxic. This is the chemical used to create clear and virtually unbreakable polycarbonate, used in drinking bottles popularized by Nalgene but now used by many others manufacturers. BPA has been shown to disrupt the hormonal systems of animals. [Just today Nalgene announced it will stop using the plastic because of growing concern over BPA. Check out the New York Times article.]

A couple of years ago my wife and I made the shift to stainless steel drinking bottles, both for ourselves and for our kids. We use the brand Kleen Kanteen, which produces stainless steel bottles with a variety of interchangeable caps. My wife and I use the standard sports bottle cap while our younger kids use "sippy" caps. (I do have to admit that I still use standard plastic sport bottles -- the kind you can squeeze -- when I'm cycling, but I try not to let the water sit for long.)

If you use bottles made of hard polycarbonate plastics I'd recommend discarding them and looking at other alternatives. Also, if you haven't done so already, you'd be wise to get rid of insulated coffee/tea cups and mugs that have plastic liners. Look for all-steel varieties. Even though they might not contain BPA, all plastics leach some amount of petrochemicals. Also, I prefer stainless steel rather than aluminum since aluminum is often sealed with dangerous chemicals. Uncoated aluminum also has problems, as it breaks down over time.(Click here for an interesting article regarding research on aluminum drinking vessels.)

What I find most troubling, however, is the pattern of denial on the part of our own governmental agencies (the FDA, USDA and EPA, particularly) in the face of growing concerns about products or practices that might adversely impact industry. Two examples immediately come to mind. Several years ago Health Canada made an announcement about the dangers of Bovine Growth Hormon (rBGH) in milk. While rBGH has been banned in Europe and Canada for several years now, the FDA, Environmental Protection Agency and Department of Agriculture continue to license the drug, and, as the result of industry pressure, rGBH milk (just like many genetically engineered foods) are NOT required to carry identifying labels.

The second example involves the use of Polytetraflouethylene (PFTE) and Perfluorooctanoic acid (PFOA), chemicals used to create Teflon for non-stick cookware as well as stain resistant fabrics. After years of concerns, DuPont, the chief developer of these chemicals, agreed to a settlement with the EPA, admitting that it neglected to report health safety information about PFOA for 20 years.

As a result of our own agencies' foot dragging and industry coddling I would suggest you pay more attention to the announcements by Health Canada and other international health agencies. Why not err on the side of caution, particularly since there are clear alternatives?

Season-Starting California Tour

I just returned from a short but sweet 3-day bike trip in California. I'm a big proponent of inaugurating your "season" with a big event of some kind. Each year I plan a spring bike trip with my brother, Jeremy, who lives in Mountain View. It's one of the few times each year I get to see him, and it provides much time on the bike (and at cheap hotels) to catch up.

[Photo: A break along the Big Sur Coast before our big climb. From left: Don, Paul, Fred (me), and Jeremy]

Several years ago, when cycling began to take over my life, I convinced Jeremy to buy a road bike. Fortunately I had some help on the campaign from Jeremy's co-worker and eventual cycling partner, Don. Since then, Jeremy, Don and I (accompanied at times by others) have taken a mini-tour each spring. Each tour is structured essentially the same way. I fly in around noon on day one and we do a short 30-40 mile tune-up ride that afternoon. Days 2 and 3 are harder, with 60-75 miles and more climbing. It's been a great way to start the biking season. To date we've toured Sonoma (CA), Scottsdate/Sedona/Flagstaff (AZ) and now Monterey/Carmel/Big Sur/King City (CA).

This year we were joined by Don's friend Paul, who served as our lead tour guide. Paul rides the route we took a few times each year with his son. In addition to his expert guiding skills Paul is a great conversationalist. I know all three of us would agree we hope Paul can join us for any and all future tours.

Here are a few photos Paul took during the trip (thanks Paul!). I'll update this post soon with a map and additional information about our route.

The Big Sur Coast looking north, toward the Bixby Bridge. The Tour of California crossed this bridge a few weeks earlier.

Enjoying a delicious breakfast at Deetjen's. Try the oatmeal!

A view of one of California's famous 21 missions, San Antonio de Padua, near Jolon, CA.

Another nice coastal view, compliments of Paul (a fine photographer).

Column 1: Buying a New Bike

In April I began a monthly Shifting Gears column in the Minneapolis Downtown and Southwest Journals, with a focus on biking in the metro area. This blog will provide an opportunity to share additional information that couldn't be included in the print edition.

My first column focused on "Buying a New Bike." Here are a few additional points I didn't have space to include in the print story:

• I wasn't able to include much information about other styles of bikes beyond the broad, and nebulous categories "road, mountain and hybrid." This meant I had to overlook, for instance, the venerable class of recumbents, whose proponents are both numerous and passionate. Likewise, I dissed BMX and stunt bikes, which have become very popular again, and not just among young people.
  
• Within the road bike category there are also far more subspecies than simply touring and racing. Time trial bikes have risen in popularity not just among time trial specialists but triathletes (who seem to be reproducing like rabbits these days). Track bikes are worthy of mention, since track racing is making a resurgence both in terms of participation and as a spectator sport. I hope to make my first trip to the Velodrome this season and maybe even enter a beginner's race.
• Perhaps most egregious is the catchall category of hybrid. This label has simply come to mean not road and not mountain. That leaves a lot left over. Putting cyclocross bikes in the same camp as cruisers and comfort bikes, for instance, would be sacrilege to many of the guys I ride with on weekends.

One other recommendation I have for those looking for a new bike had to be cut from the story. I know there will be many dissenters to this opinion, but I'd recommend sticking with a major bike maker if this is your first bike purchase in a while. By that I mean, look at models from Trek, Cannondale, Specialized, Giant, Bianchi, etc. They tend to have better warranties (though they also have better lawyers) and if you have a problem it's more likely your shop has another one just like it. Once you fall in love all over again with cycling you can make your next purchase a high-end, custom-built carbon fiber beauty made by hand by some guy in his one-room shop in California (or a tiny village in Italy).

There are many more points I could have made in this short piece but these will have to suffice for now. The next installment in the Shifting Gears column is focused on tips for would-be bike commuters. It should be out in early May, just in time for Bike-to-Work Week (May 12-16).

Until then, happy riding!