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february 2016yogajournal.comGet to know the different ways your muscles
contract to power up your asana practice.Body of knowledge
Understanding your muscle tissue
By Joe MillerANATOMY
practice well
THERE’S A REASON your yoga teachers say things like, “Eccentrically
contract your triceps to slowly lower into Chaturanga,” instead
of just, “Contract your triceps.” It’s because there are three dif-
ferent ways a muscle can contract, and how you utilize these
actions can affect strength and safety in a pose. So, what
is really going on inside the muscle tissue when we fl ex,
and why does it matter?
To get a feel for the mechanics in question, bend your
elbow. The biceps on the front of your arm contracts to lift your
forearm, creating a shortening of muscle fi bers, or concentric
contraction. If you keep your elbow bent, your biceps stays con-
tracted to resist gravity in a static (nonmoving), or isometric,
contraction. These types of contractions probably feel famil-
iar—they’re what you’d do if you wanted to “make a muscle.”
Now slowly lower your forearm. You might assume that
the triceps muscle on the back of your arm, which is responsible
for straightening your elbow, is working now. However, because
gravity pulls your forearm down, your triceps doesn’t need to do
anything. Rather, your biceps continues to contract as it length-
ens, resisting gravity. If it didn’t, your forearm would simply
fall. Such lengthening, or eccentric contractions, are critical
to controlling many movements, from folding forward into
Uttanasana (Standing Forward Bend) to jumping back to
Chaturanga Dandasana (Four-Limbed Staff Pose) to moving
into an arm balance like Parsva Bakasana (Side Crane Pose).
Targeting concentric, isometric, and eccentric contractions
in your asana practice will work your muscles through their full
range of motion, helping you to develop balanced strength and
lessening your risk of injury. To understand these contractions,
you need to know what happens in your muscles when they’re
working. Muscle cells, or fi bers, contain many smaller strands
called myofi brils, each of which in turn is comprised of a series
of contractile units called sarcomeres. Within the sarcomere, two
types of protein fi laments—thick fi laments called myosin and
thin fi laments called actin—overlap like interlaced fi ngers.
When a muscle like the biceps contracts concentrically, a sig-
nal from the central nervous system prompts the thick myosin
fi laments to catch hold of nearby thinner actin fi laments, form-
ing linkages called cross-bridges. If the pull is strong enough to
overcome opposing resistance (usually from the force of gravity),
continued on page 5o ILLUSTRATION: MICHELE GRAHAMMUSCLE
FASCICLEMYOFIBRILMUSCLE CELL
(FIBER)SARCOMEREBICEPS
MUSCLEMYOSIN
ACTINCROSS-BRIDGE