Today we accept the existence of different muscle fiber types as part of muscle physiology. The distribution of these fibers helps to determine our ability to be successful at different endeavors, influences our gains from training, and may represent one genetic ceiling to our performance. The idea here is that there is a continuum in terms of muscle fiber types with slow twitch muscle fibers on one end of the spectrum and fast twitch on the other end. Slow twitch produce a very small amount of force, but are able to maintain it for a long period of time. Fast twitch produce a large amount of force, but fatigue very quickly. We’re all born with a certain percentage of each and it does not seem possible to increase your percentage of fast twitch fibers – so if you want to be good at explosive sports you’d need to pick your parents carefully.
Costill et al (1976) had one of the first studies looking at this. Not only is this a groundbreaking study, as it established that athletes from different events have different fiber type distributions, but it is still heavily referenced in textbooks today. The authors studied 40 track and field athletes as well as 21 untrained men and women. The types of athlete are broken down below, their performance, and (where I can find it) the world record in that event in 1976:
| Event | Gender | Number of Athletes Studied | Mean Performance | World Record |
| 100 meter sprint | M
F |
2
2 |
10.5
11.4 |
9.9
11.01 |
| 800 meter | M
F |
7
7 |
1:51.5
2:08.1 |
1:43.5
1:54.94 |
| 5 K
Marathon |
M | 5 | 14:09
2:44:00 |
13:13
2:09:12 |
| Long Jump
High Jump |
F
M F |
3
2 3 |
5.92 m
7.96 1.84 |
8.90 1.96 |
| Javelin | M
F |
3
3 |
78.6
51.8 |
94.58
|
| Shot Put
Discus |
M
M F |
4
4 2 |
19.3
61.1 54.8 |
22
|
| Untrained | M
F |
11
10 |
For this study, the obtained muscle samples from the lateral head of the gastrocnemius. Their rationale being that other muscles (deltoids, quadriceps, etc.) may be important, but the gastrocnemius is one muscle that is going to be used by every athlete studied. The authors also looked at enzymes for these athletes and in a smaller sample (17 athletes, 16 untrained individuals) they studied maximal oxygen consumption on a treadmill. Of the athletes studied, only two were not middle- or long-distance runners. The correlation between slow-twitch fiber percentage and maximal oxygen uptake was very weak (0.13), but the correlation between the enzyme succinate dehydrogenase and maximal oxygen uptake was very high, 0.79.
Costill et al examined both the percentage of muscle fibers that were fast or slow, but also the relative area of the muscle occupied by both fast and slow. I have collapsed this information down into sprinters, distance (middle + long), jumpers, throwers, and untrained below:
| Event | % fast twitch | % area fast twitch |
| Sprinters (F)
Sprinters (M) |
72.6%
76% |
73.2%
76.5% |
| Distance (F)
Distance (M) |
39.4%
39.35% |
39.6%
45.6% |
| Jumpers (F)
Jumpers (M) |
51.3%
53.3% |
56%
61.2% |
| Throwers (F)
Throwers (M) |
53.3%
55.95% |
55.1%
59.15% |
| Untrained (F)
Untrained (M) |
49%
47.4% |
51.2%
44% |
This study demonstrated that sprinters and distance runners have very different fiber type distributions, which should not be a surprise. Now, the information on the jumpers and throwers should be interesting (after all, there is not as strong a trend towards fast twitch as I would expect). There could be several reasons for that. First, the authors are only studying the gastrocnemius, the fiber type distribution might be very different in the hamstrings and quadriceps. Second, the athletes studied in the jumpers and throwers had performances that were far from the world record. Third, it’s a small sample of jumpers and throwers relative to all the athletes performing the event.
The three reasons described that might influence the jumper and thrower performance need to be applied to the results of the entire study as well. It’s a small sample size (four sprinters total for example). It’s one muscle being studied. The athletes are collegiate track and field athletes, but they are not world class. Taking all of this into account, one has to be comfortable with sweeping statements like: “100 meter sprinters are 72-76% fast twitch muscle fibers.” This was a ground breaking study and demonstrated that different events have muscles that are made up of different fiber types, but it had limitations and could not be used as something that developed universal truths.
Costill, D.L., Daniels, J., Evans, W., Fink, W., Krahenbuhl, G., and Saltin, B. (1976). Skeletal muscle enzymes and fiber composition in male and female track athletes. Journal of Applied Physiology, 40(2): 149-154.
