SYMPOSIA PAPER Published: 01 January 1987

Contribution of the Musculature to Rotatory Laxity and Torsional Stiffness at the Knee


The relationships between the mean rectified electromyogram (EMG) from two muscle groups crossing the knee joint and the rotational stiffness and laxity about the longitudinal axis of the lower leg were investigated. The EMG signals from three of the quadricep muscle group and two of the hamstring muscle group were monitored using surface electrodes. Each subject sustained self-induced muscle activity from specific muscle combinations while a torque rotating the foot medially and laterally is externally applied. Joint rotation is measured using an electrogoniometer.

Analyses of the data showed increased joint stiffness with increased numbers of active muscles. The stiffness measurements ranged from 0.16 to 2.54 Nm/degree depending upon the combination of active muscles. The stiffnesses measured in different tests were very repeatable with standard deviations ranging from 0.02 to 0.25 Nm/1°. Increases in joint stiffness of over 400% by activation of these muscles were measured.

Author Information

Louie, JK
University of California, Berkeley, CA
Mote, CD
University of California, Berkeley, CA
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Developed by Committee: F27
Pages: 26–52
DOI: 10.1520/STP23173S
ISBN-EB: 978-0-8031-5003-4
ISBN-13: 978-0-8031-0936-0