| The sensation of joint stiffness is frequently observed after
eccentric contractions (ECs) in human, but the joint stiffness of
animals after ECs has not been examined previously. This study tested
whether a bout of ECs affects rat ankle joint stiffness. We also evaluate
muscle passive tension in the rat hindlimb to examine the relationships
of ankle joint stiffness with muscle passive tension. Anesthetized
male Wistar rats (n = 23) were firmly secured on a platform in the
prone position. A bout of ECs was performed on the gastrocnemius muscle
with a combination of electrically induced tetanic contractions via
a skin electrode and simultaneous forced dorsiflexion of the ankle
joint (velocity, 15°/s; from 0°to 45°). Passive resistive torque (PRT)
of the ankle joint was measured to evaluate joint stiffness. Passive
tension of the exposed gastrocnemius muscle was also measured when
the maximum value of joint stiffness was obtained. The PRT on days
2, 3, and 4 was significantly higher than the pre-treatment value
(days 2 and 4; p < 0.001, days 3; p < 0.01). The passive tension
on day 4 was significantly higher than that of the sham-operated group.
The muscle wet mass was identical in both groups, suggesting the absence
of edema. We conclude PRT increases after ECs in rat ankle joint.
We also show the possibility that it is associated with muscle passive
tension, independent of edema formation.
KEY
WORDS: Lengthening,
flexibility, passive torque, passive tension, animal model.
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