Came across this summary of Saltin's work which I thought would be of
interest to the list:
*******
Even wonder what makes a great athlete? Why did Marion Jones of the
U.S.A. win the gold medal in the 100m sprint in Sydney in a time of 10.75
seconds? And how did Japan's Takahashi run the women's marathon (a distance
of over 42 km - that's approximately the distance between Calgary and
Airdrie!) in 2 hours, 23 minutes? Perhaps it has something to do with their
physiology - their muscles. In a recent article in Scientific American,
researchers have discovered the functions of different muscle fibers and
their contribution to athletic performance.
Skeletal muscle is composed of a bundle of cells called fibers and each
fiber is composed of thousands of strands called myofibrils. It is the
myofibril that causes the contraction of the muscle in response to nerve
impulses from the brain. In turn, each myofibril is composed of sarcomeres
that contain two proteins, myosin and actin, that cause the actual
contraction. A component of the myosin molecule called the heavy chain
determines the function of the muscle fiber. There are 3 different types of
heavy chains or isoforms: I, IIa, and IIx. The type I isoform is referred
to as a slow fiber and the IIa and IIx isoforms are called fast fibers.
The slow type I fiber relies on aerobic metabolism making it important in
endurance sports such as the marathon. The fast type IIa and IIx fibers
rely on anaerobic metabolism and are crucial to sports like sprinting that
require powerful but short bursts of energy. The researchers hypothesized
that endurance athletes should have a greater proportion of slow type I
fibers in their quadriceps muscles compared to sprinters. They found that
this was the case. More interestingly however, it seems that through a
weight training regiment, some fast IIx fibers are converted to IIa fibers.
Oddly enough, no study has been able to confirm if it is possible to turn
fast type II fibers into slow type I. The implications of this are that
marathon runners are born great athletes and not made. The large proportion
of slow type I fibers in their muscle cannot be built up like sprinters who
can through training convert their slow type I fibers into fast type II
fibers.
Interesting Facts about Muscles:
· An average active adult has approximately
50% of each fiber type (slow type I and fast type II)
· Fast IIx fibers contract 10 times faster than
slow type I fibers
· A person with a spinal cord injury has almost no
slow type I fiber in their muscles because the lack
of electrical stimulation causes atrophy of this type
of muscle
· Disuse of a muscle can shrink its size by up to 20%
in 2 weeks!
· Gene therapy in the form of an injection of artificial
genes into an athletes' muscle cells may be the
performance enhancing drug of the future; this type
of doping may be impossible to detect
Source: Andersen, Jesper L., Peter Schjerling, and Bengt Saltin.
2000. Muscle, Genes and Athletic Performance.
Scientific American 283: 49-55.
--
Jon Entine
RuffRun
6178 Grey Rock Rd.
Agoura Hills, CA 91301
(818) 991-9803 [FAX] 991-9804
http://www.jonentine.com
