Affiliations: [a] Department of Medical Anatomy, Section C, The Panum
Institute, University of Copenhagen, Blegdamsvej 3C, DK-2200 Copenhagen N,
Denmark | [b] Laboratory of Human Physiology, The August Krogh
Institute, University of Copenhagen, Universitetsparken 13, DK-2100 Copenhagen
O, Denmark | [c] Institute of Medical Physiology, The Panum Institute,
University of Copenhagen, Blegdamsvej 3C, DK-2200 Copenhagen N, Denmark
Note: [] Corresponding author: Hendrik Sorensen, Department of Medical
Anatomy, Section C, The Panum Institute, University of Copenhagen, Blegdamsvej
3, DK-2200 Copenhagen N, Denmark. Tel. +45 35 32 72 35; Fax: +45 35 32 72 17;
E-mail: h.sorensen@mai.ku.dk
Abstract: During strength measurement using isokinetic dynamometers great care
is usually taken to align the anatomical joint axis to the rotation axis of the
machine's lever arm. This ensures agreement between joint angular
position/velocity and the corresponding measurements from the machine's
potentiometer. We examined the accuracy of this correspondence during
concentric knee extension with subjects sitting upright and strapped to the
machine's chair. Extensions were performed at 30 dg, 120 dg and 240 dg with
range of movement from 90 dgz knee flexion to full extension. We observed that
due to compression of the soft tissue at the back of the thigh and elevation of
the pelvis (despite strapping) the anatomical joint axis moved downward
relative to the rotation axis of the lever arm. This caused discrepancies
between joint angle measurements from the machine and from a knee-mounted
goniometer of up to 33 dgz. These circumstances should be taken into account
when muscle force-length-velocity relation studies are conducted using
isokinetic machines.
