抄録
The sense of position is signaled mainly by muscle spindles. Isometric muscle contraction at a shorter (hold-short conditioning) length causes an increase in Ia afferent discharge after the muscle returns to its intermediate length by means of intrafusal muscle thixotropy, and hold-short conditioning in the biceps has been shown to produce limb position-sense errors. The contraction of muscles in the human upper body reinforces tendon jerk in the lower limbs, which is referred to as Jendrassik maneuver (JM). JM increases stretch responses of muscle spindles preconditioned with hold-short conditioning. Consequently, these findings suggest that JM would enhance the history-dependent position-sense errors that result from intrafusal muscle thixotropy. We studied the effects of quadriceps contraction (QC) on upper-limb position-sense errors induced by hold-short conditioning in the biceps of 12 healthy men. QC enhanced tonic vibration reflex of the biceps, suggesting it also has a reinforcement effect on stretch responses of muscle spindles similar to JM. After hold-short conditioning, subjects perceived that the conditioned forearm was placed in a more extended position than occurred in reality. This position error was more obvious after hold-short conditioning combined with QC. These results suggest that QC and hold-short conditioning work together efficiently to develop intrafusal muscle thixotropy. [Jpn J Physiol 55 Suppl:S119 (2005)]
