Download How your muscles contract

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Scott Riewald,PhD,CSCS,NSCA.CPT
How Your Muscles Contract...
hink about your muscles.
They are quite amazing StructUres. When they contract
they generate large forces and
aluse your joints to move. They also provide stability to
your body; without muscles your entire body would 001lapse to the floor. But there is a lot more to muscle than
meets the eye. After a hard day of skiirtg yoU can likely tell
that your muscles were active by how sore they become.
But did yOU know that there are three different ways that
muscle cah contract? Well there ate, and we are going to
discuss each type of contraction briefly and why they are
important for skiing;
Concentric Contractions
Concentric contractions are shQrtening contractions; as
the muscle contracts it shortens its length and causes
movement about a joint. This is the type of muscle con~
tractiM we are mOst familiar with.
Eccentric Contraction
An eCcentric OOntractibnis also known as a lengthening
contraction. The force that the muscle is generating is 1&
than the external load. This is observed in three of the four
quadriceps muscles while skiing everytime yOUrknees bend to
absorb the bodyweight. In the gym, while using free weights an
eccentric contraCtion is observed every time the weights are lowered. The muscle soreness you experience aJier liJiing weight or
skiing is &equentlydue to small microtraumas to the muscle that
commonly accompany eccentric contractions
NSCNs Performance Training JoUrnal
Isometric Contractions
The prefix iso- means "equal" or "the same" So isometric means
"equal length." In an isometric contraction the muscle length
does not change. Stand in a doorway and press both hands outward against the doorframe. YOUrmuscles are definitely active,
but there is no movement-the mUsclesare hOtchanging length.
This is an example of an isometric contraction.
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There is another type of isometric contraction that does result in
the movement of a joint or joints; Many of the muscles in your
body control movement primarily at only one joint. 'think of
your biceps muscle. When It contracts it €aUsesyour elbow to
bend. That is the muscle's primary ftlnction. However, now
think about the muscles that eXtendyoUrknee -the qiliidriceps
mUscles.FOUrmuscles make up the qUadriceps:VastiIsLateralis,
V:iStusMedialis, VastiIs Intermedhls, and ReCtUsFemoris.Three
of them control knee extension, and only knee extension.
However, one of the four, the ReCtusFemoris muscle, also flexes
the hip when it contraCtS.When this muscle undergoes a concentric contraction it will cause the knee to extend and the hip
to flex. It is possible that the hip and knee tall move in such a
way (like extending the knee and extending the hip) so that the
length of the ReCtus Femoris remains constant-an isometric
contraction-even though mOvement occurs at both joints.
All three of these contractions, concentric, eccentric and isometric, occur when you ski. It is easyto pick out the concentric contraCtions; every time you move a joint, whether it is bend your
knees as you carve a turn or extending your elbow as you plant a
pole, yotl are contracting muscles concentrically. Eccentric and
isometric contractions are a bit more difficult to spot. Yourthigh
muscles, the quadriteps and hamstrings, experiente eccentric
contractions every time you cushion yourself on a landing or as
you go through a mogul field. Also the core muscles of your
body, your abdominal and lower back muscles, contraCt isometrically as you try to maintain balance and stability on your skis.
You always knew muscles were important for skiing. They generate force and help you to move swiftlyand freelyover the snow.
However, there's a lot more to how a muscle functions than we
may realize. Now you know a little more about the different
types of muscle contractions and how they caIi be used iii skiing.
About the Author
Scott Riewald, PhD, CSCS; NSCkCPT, is currently the
Educational ProgramsCoordinatorJor the National Strength and
Conditioning AJsoi:iation(NSCA). Prior to joining the Staff at
NSCA, he wasthe BtomechdntcsDbwtof for USA Swimmingfrom
1999-2002, where he developedbiomechafiicttltesting, research
and edUtationalmaterialJoI' the National 'Ram: He obtained his
PhD from Norrhwesum University in Biomedical Engineering!
Biomechanics and is a Certified Strength and Conditioning
Specialist((:"5C5).SCottalsoworkedftr the Us Olympic CommitUe
asa researchassistantand has developedtesungprotocolsfor anum"
ber of sports. Scott has worked with individuals who rangefrom
Olympic caliber athletes to persons who have suffered
NSCA's Performance Training Journal
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