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Hinrichs, Rick
04-08-1993, 11:04 AM
Dear Biomch-l subscribers:

As part of a course that I am teaching I was asked a question that I could
not answer right off the top of my head and I thought some of you might be
able to help. The way I understand it from reading White and Panjabi's
textbook, when one flexes the trunk from a standing position (as if to bend
over to pick up a box from the floor), the extensor muscles (presumably
the erector spinae principally) are active until one gets to full flexion at
which time the muscles become silent and the ligaments take over to provide
the extensor moment. My question is: Which ligaments provide the bulk of
this extensor moment and what are their moment arms about an assumed axis of
rotation within the disc compared with the extensor muscles? WHICH HAVE THE
GREATER MOMENT ARMS, THE LIGAMENTS OR THE MUSCLES? From looking at White
and Panjabi I noticed that the ligamentum flavum is situated fairly close to
the spine whereas the supraspinus ligaments are more superficial, so I guess
the answer depends on which ligaments contribute the most to the extensor
moment. Thanks in advance for any information you can provide.

Best regards,

--Rick

Richard N. Hinrichs, Ph.D.
Associate Professor
Dept. of Exercise Science
Arizona State University
Tempe, AZ 85287-0404 USA

email: Hinrichs@ESPE1.LA.ASU.EDU
or atrnh@ASUACVAX