Super fast-twitch fibres, the secret of the sprint stars

Translation from French to English of original blog by Pierre-Jean Vazel in Le Monde:

What do a sprinter, a lion and an astronaut have in common ?  The answer can be found in their muscles: they all have a similar proportion of super fast-twitch fibres.  Among the wide variety of muscular profiles, the quality of the fibres of the world’s fastest athletes is closer to that of big cats, people spending time in space or even those suffering from spinal cord injuries!  Dr. Scott Trappe, Director of the Human Performance Laboratory at Ball State University (Indiana) and NASA researcher, explains these unexpected similarities after analysing a sample taken from the thigh muscle of Colin Jackson, 60m hurdles World Record holder (7.30 seconds).  His paper “Skeletal Muscle Signature of a Champion Sprint Runner”, just published in the Journal of Applied Physiology, constitutes the first description in a scientific review of the muscle fibre composition of a world class sprinter.

Colin Jackson, the cat-like sprinter

Images of the procedure appeared in a BBC documentary shown in 2008 about the physical and mental talents of the Welsh hurdler (two-time 110m hurdles World Champion and European Record holder since 1993), and sprinter: European Indoor 60m Champion in 6.49 sec., a time only 0.1 sec. slower than the current World Record.  The Making of Me shows the retired athlete undergoing a biopsy to collect a sample of thigh muscle tissue.  Biologists then had to identify the different fibres and test their biomechanical properties.  “It took us two years to complete the analysis, says Dr. Trappe.  Because of the unique results, we wanted to repeat certain experiments in order to be sure they were correct.”  The conclusion is surprising: Colin Jackson possesses an amount of “super fast-twitch” fibres observed only in those suffering from spinal cord injuries, which are as powerful as those of the lion and the caracal. “Examples in the animal world are more closely linked to our results for this athlete and make these measurements more meaningful.” Analyses used to be based on fibre colour.  The first description of white and red muscles (in the same rabbit’s paw) can be found at the beginning of a work dating from 1678, Observations on Torpedoes by the Florentine doctor Stefano Lorenzini.  However, fibres are now classified according to their contraction speed, although there is a real continuum between the slowest (type I) and the fastest (type IIx), passing through all intermediate stages.  Their distribution varies from one person to the next and according to the function of the muscles: solearis, which helps to stabilise the leg, only contains 10% of fast-twitch fibres, while the orbicularis oculi muscle, which makes the eye blink, contains 90%.  Biopsies on athletes are usually performed on the vastus lateralis muscle of the thigh, where the proportion of slow and fast-twitch fibres is almost the same in humans, which allows the distinction to be made between endurance and explosive athletes.

Slow-twitch fibres                                  fast-twitch fibres twitch table

Proportions of different fibres, from slowest to fastest-twitch, in Colin Jackson compared to those of Danish sprinters

In Colin Jackson’s case  there is no ambiguity: in the continuum of all the muscle types from his vastus lateralis, Dr. Trappe’s team found only 29% slow-twitch (I), and, in particular, 32.5% pure fast-twitch fibres (IIx).  The latter are very rare in sprinters whose biopsies have appeared in scientific publications ; for example only 0.2% were found in P. Andersen’s group of Danish sprinters in 1994, which included the then national record holder with 10.47 sec.  “Until we had this data for the elite sprinter, a high number of these super fast-twitch fibres in humans was limited to the loss of use of muscles caused by extreme immobilisation following a spinal cord injury”, says Dr. Trappe, whose team have analysed over 60,000 human fibres taken from a wide variety of individuals.  Furthermore, muscle fibre plasticity is well-established in both humans and animals.  “Bedrest causes an increase in hybrid IIa/IIx fibres, but not a lot in IIx.  A transition from slow-twitch to fast-twitch has also been observed in astronauts in weightlessness, due to a drop in activity, but it is limited compared to spinal cord injury patients.”  The Jackson case is therefore of interest to the researcher.  “It’s the first time that such a high proportion has been observed in a healthy muscle and it therefore represents a paradigm shift in the understanding of human physiology that opens the doors to other research in the field of medicine and performance.” Although biopsies of athletes are nothing new, there are not enough points of comparison.  The first case (and the fastest subject) recorded in the literature is that of an American sprinter who I discovered was called Norbert Payton.  World ranked 38 over 100m with 10.2 sec., this small-framed (1.65m) sprinter famed for his explosive start only has 26% slow-twitch fibres according to the research published in the same year by Dr. Philip Gollnick of the University of Washington.  However there is no indication of the amount of super-fast twitch fibres IIx, incidentally called IIb at the time.  If Dr. Trappe remembers that the work in the 1970s and 80s did not benefit from the sensitivity of modern muscular profile testing techniques, we have no choice but to make do with it and to turn to the archives of certain coaches of the time.

Nelli Cooman, the human bomb

The most advanced in this field is Dutchman Henk Kraaijenhof, most famous for coaching the queen of the boards Nelli Cooman, two-time World Champion and six-time European Indoor Champion over 60m between 1985 and 1994.  “I have a lot of data but as I am not a scientist, I haven’t published it.”  However, he does give me the results of the first biopsy (dated 26th April 1985) conducted by Dr. Guillermo Laich on the little orange bomb who measured 1.58m for 62kg.  Unlike Colin Jackson, equally talented over 60m and 110m hurdles, she was not as successful over 100m, where her IIb fibres, while very explosive, were too energy-hungry and turned into a handicap. Type 1 : 28,1 % Type IIc : 0,0 % (corresponds to type I/IIa in the analysis of Jackson) Type IIa : 30,9 % Type IIb 41,0 % ! (corresponds to type IIa/IIx and IIx) In 1986, Cooman’s training was geared to the short sprint, which culminated in her setting a new World Record in the blistering time of 7 seconds flat.  A second biopsy was carried out on 8th October to examine the differences.  In certain cases, after a specific kind of training, transitions from intermediate to fast-twitch fibres have been observed.  Not so in Cooman’s case: “The main change was in the size of the fibres, not really in the percentage.  Possibly because hers were already close to the limit of the spectrum!”  Hypertrophy, which represents the distribution of large muscle fibres, went from 0 – 23%!  Having large fast-twitch fibres is an advantage, as imagined by the coach: “It’s as though instead of having 8 marathon runners weighing 50kg to push a car you have 4 bodybuilders weighing 100kg.”  According to Dr. Trappe, looking at Colin Jackson’s data, « it appears that the fibre type profile and the power generated by the fast-twitch fibres provide a solid foundation to suggest that these characteristics go a long way to explaining the sprinting success of this individual.”

From the track to the stars

In his blog, Henk published photos of the biopsy of Cooman and her then training partner Merlene Ottey, whose 60m World Record she broke.  However, her slow-twitch fibre percentage was close to 40%.  It must be said that the tall Jamaican was much more comfortable over 200m and that she came into the sport via cross-country!  “Luckily, sporting performance is complex, and is rarely decided by a single dominant factor.  There is always room for compensations…Technical and emotional factors, coaching and lifestyle also play an important role.”  In examining the literature, I was able to find extreme proportions in sprinters: from 93.7% of fast-twitch fibres (the same as a leopard!) for a certain “A.I.”, a 26 year-old Japanese athlete (1.74m for 68kg), who had run 50m in 5.8 seconds, against only 31% for a sprinter in the West German national team (after Fekete, 1987).  If we turn our attention to endurance specialists, we notice an equally wide range: Fink’s 1977 study of US long distance runners gives 2% for Gary Tuttle (2h 15min in the marathon) compared to 50% for his teammate Don Kardong (4th in the marathon in the 1976 Olympics in 2h 11mon 16s)* Mary Decker, World 1500m and 3000m champion in 1983 was only shown to have 35% slow-twitch fibres, i.e. slightly fewer than Merlene Ottey!

The fact that these exceptions do not really confirm the rule in a way saves athletes from genetic determinism.  Thanks to the Jackson case, the carrying out of sports biopsies, which fell out of favour at the end of the last century, may be readopted as a way of evaluating the response of fibres to the demands (or lack of) physical exercise.  As for the astronauts of the International Space Station monitored by Dr. Trappe, training plays an essential role in the prevention of an even greater transition of slow-twitch to fast-twitch fibres and in the ensuing motor dysfunction, as their role does not really require the muscle qualities of an elite sprinter! “We are now working with NASA on new training programmes that incorporate more high intensity exercises, in the hope that this is a more efficient way of maintaining the health and muscle performance of the astronauts while they are in space.”  Training conditions fibres, but, conversely, to what extent should fibres condition training ?  For my next blog article I interviewed a former World Championship finalist over 100m and 200m, whose biopsy showed that he possessed 69% of IIb fast-twitch fibres, which is even more astonishing than the cases of Jackson and Cooman, and which is not documented in any scientific publication.  He talks about how he salvaged his career by radically changing his training after discovering this genetic characteristic.

* In Fink’s original publication it gives 27% slow-twitch fibres for Steve Prefontaine (holder of all national records from 2000m to 10,000m at the time), i.e. 73% fast-twitch fibres, but this is probably a typo.  The correct figures should be 72% slow-twitch and therefore 28% fast-twitch.


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