Motomi Igari, OTR, MS, Yutaka Tomita, RE, PhD, Hiroyuki Miyasaka, OTR, PhD, Abbas Orand, RE, PhD, Genichi Tanino, RPT, MS, Kaoru Inoue, OTR, PhD, Shigeru Sonoda, MD, PhD
Jpn J Compr Rehabil Sci 5: 141-146, 2014
Objective: To develop a method to measure knee joint
resistance torque during passive motion by using
isokinetic equipment (e.g., the Biodex, Cybex, and
Kin-Com).
Method: We used the Biodex System 3 isokinetic
equipment in the present study. To determine the
resistance torque in human knee joints, we first
established a method to correct for the torque due to
gravity and inertia, based on the angle, angular
velocity, and torque output from this equipment.
Thereafter, to estimate the active torque due to muscle
contraction, we measured the electromyograph (EMG)
signals and fitted a potentiometer on the driving arm of
the Biodex to synchronize the EMG signals with the
Biodex output.
Results: At the angle Į0, and denoting the torque that
occurs in the lower leg due to gravity as T0, the torque
due to gravity (Tg) at angle Į is given by Tg=T0 cosĮ/
cosĮ0. Denoting the moment of inertia of the lower leg
as I and the angular acceleration as a, the torque caused
by inertia (TI) is given by TI=I a. Letting the value of
the torque that is output by the Biodex be Ttotal, the
resistance torque caused by the subject (T) is given by
T=Ttotal-Tg-TI. The changes in T that occur simultaneously
with the EMG signals indicate the active
torque that is caused by muscle contraction.
Conclusion: We measured the resistance torque that
occurred during passive joint motion by correcting for
the angle, gravity, and inertia, based on the angle and
torque that were output by the Biodex. The joint
torque, angle, and EMG signals were measured
simultaneously by monitoring the output of a
potentiometer mounted on the arm of the Biodex.
Key words: joint stiffness, quantification, muscle tension, viscoelasticity, electromyogram