My understanding has always been that humans have two basic kinds of muscle - “fast” and “slow.” Fast helps you jump high, run fast for short distances, etc. Slow helps you do things that require endurance.
In another thread, another person referred to this theory as “disputed or mythical.”
Some muscles, such as those involved in intestinal contractions, have structures which are optimized for slow repetitive contractions. The number of mitochondria per gram of muscle in these cells, and the oxygen transport capacity of the associated blood vessels are much lower than in muscles like the fruit-fly wing muscle which contracts many times a second. If you hooked up a slow muscle to the wings of a fly it would rapidly lose its’ ability to contract as the mitochondria would run out of the oxygen needed to make ATP. Anaerobic metabolism might be able to keep things going for a bit, but that always leads to lactic acid buildup and fatigue. The structure of muscles is more varied than can be accurately described with the fast-slow concept. The structure of individual muscles, heart, gut, leg etc. is optimized for each muscles particular function. That said, fast still helps you jump high, and slow helps you digest that yummy cheeseburger after the meet.
There are actually five types of muscle fibers, but dividing them into two types (fast and slow) is easier.
No, it is not a myth. I remember reading the results of a muscle biopsy done on Alberto Salzaro, a world record holder in the marathon, who had allegedly 92% slow twitch fibers in his calves.
The relative proportions of fast- to slow-twitch fibers is genetically determined, and cannot be altered by training. Elite athletes are made, not born.
If you are interested in strength-related activities, another factor that goes into strength-related performance is ability to recruit fibers into one effort. This is affected by genetics, but can be increased with training. This accounts for a good deal of the early gains experienced by many trainers who start weight lifting for the first time. Other factors are limb length (shorter arms and legs improve performance in most lifts, as you then need to move the weight a shorter distance. Naim Shuleimanov, the phenomenal Olympic lifter from Turkey, is only 4 feet 9 inches tall. Mike Bridges, a multi-world powerlifting champion and record holder [2105 total record in the three powerlifts, including an 837 squat] was only 5 feet 2 inches at a body weight of 181 pounds.), where the muscles attach to their bones, and other factors.
You can improve your performance in endurance events by increasing your cardio-vascular capacity, but not by changing your numbers or proportions of slow twitch fibers.
The myth here is probably that the proportions of the different muscle types vay significantly among “races”. This is often invoked as the reason that blacks tend to excell at certain sports such as basketball and sprinting, but to my knowledge, there’s exactly zero evidence for this.
Shodan, the only types I can remember from high school biology are striated and cardiac. What are the other three?
I learned that there were 3 types of muscle fibers: skeletal (attached to bones - the meat of you), smooth (intestines and blood vessels), and cardiac (heart). Both skeletal and cardiac show the striations formed by the actin and myosin fibers that pull together to do the muscle contraction while the smooth do not (these fibers are more randomly arranged). Skeletal and smooth are multinucleate and cardiac is not. Skeletal is under voluntary control (more of less) while smooth and cardiac are under autonomic control (more or less). Cardiac muscle have cool gap junctions that allow for communication between cells, coordinating the whole effort (otherwise the heart wouldn’t have a beat that we could dance to).
Skeletal muscles have (as I recall) 3 types of twitch fibers - one slow and two fast twitch. The slow is resistant to fatigue but does not give a lot of power. One of the fast types is more powerful but fatigues easily. The other fast type is more powerful than the slow type but fatigues less easily than the other fast type. You are born with the percentage of slow verses fast fibers. You can’t change the percentage of slow to fast, but you can, with training, change the percentage of the two fast types, relative to each other.
At least this is what I learned as an undergraduate, back in the Pleistoscene. Things have undoubtably change, and I’m sure someone will be along shortly to clean up the mess in aisle 6.
brachyrhynchos has got it on the different types of muscle and muscle fiber.
The September 2000 issue of Scientific American had an article on the relationship of muscle fibers, athletics, and genetics. Unfortunately, the full article is not available online. I’ll quote the summary here:
There are distinct differences in relative proportions of fast- to slow-twitch muscle fibers between athletes that excel in different types of sport. For example, the sprinter has a high proportion of fast-twitch, the marathoner has a high proportion of slow-twitch.
Note that the article has absolutely nothing to say about race.
We’ve mostly got it right so far, as I recall from my Exercise Physiology classes.
However, I seem to remember that the division between slow and fast twitch muscle fibers is not black and white. Rather, the fibers exist in a spectrum with some leaning more one way than the other. (Get it - “leaning”… they’re LEAN muscles? Never mind…)
According to Jeff Galloway - coach and running authority - fast twitch muscles are sugar-burning and fire quickly. They are not as resistant to fatigue. Slow twitch muscles burn fat and can be trained to fire repeatedly for a long time and are more resistant to fatigue. I can see how this would make a difference to marathoners vs sprinters (the ability to run for a long time). But I wouldn’t see this affecting how fast someone could run a short distance. After all, today’s marathoners are running as fast as some short distance sprinters used to!
Shodan is grossly oversimplifying but this doesn’t create a contradiction. His statement implies that those people with the best genetics for an athletic activity would generally perform the best. I think this is true all other things being equal. Of course, in RL, all other things are not equal. Some people have more desire and dedication to achieve greatness in a field. I don’t consider these genetically determined traits.
I think a more accurate statement would be “Elite athletes are cultivated.” Those found to have a higher genetic potential are usually more encouraged environmentally to succeed.
I’m pretty sure I once read that pitcher Nolan Ryan, who could consistently pitch a baseball at or just under 100 MPH had an unusually high proportion of “fast-twitch” muscles in his arms.
You don’t pitch 7 no-hitters by relying on a curve ball.
Not really, Jill, but it’s a nice thought! Charley Paddock, Harold Abrahams, and peers were regularly clocking 10.5 to 11.1 in the 100 back in the mid-20s. Now, if you are talking about sixth-rate “short distance sprinters,” maybe. Otherwise, no way. Even in the 200, today’s best marathoners would still get blown away by these guys.
These times may seem slow compared with today’s sprinters, but recall that their training and equipment were poor, the cinder tracks were terrible, and the best potential sprinters of the era were still living under Jim Crow or sharecropping down south. Not to mention the undetectable performance-enhancing drugs of today…
BTW, today’s Olympic swimmers also have concentrations of FTM in the 90s.
QUESTION: Is FT-ST muscle composition related in any way to VO^2 max and improved performance at high altitudes? IOW, do the strongest high-altitude climbers have predominantly slow-twitch muscles?