Aftereffects of mechanical vibration and muscle contraction on limb position-sense.

Mechanical vibration (MV) of a muscle causes position-sense errors during and after application. Isometric muscle contraction at a shorter (hold-short conditioning) or longer (hold-long conditioning) length causes limb position-sense errors after the muscle returns to its intermediate length by means of intrafusal muscle thixotropy. However, it is unclear whether MV enhances these thixotropic position-sense errors. We studied the after-effects of MV on position-sense errors induced by hold-short and hold-long conditioning in the biceps of 12 healthy men. After hold-short conditioning, subjects perceived that the conditioned forearm was placed in a more extended position than occurred in reality; after hold-long conditioning, a more flexed position was perceived. Use of MV with hold-short or hold-long conditioning enhanced both errors, which were most obvious at 100 HZ. These results suggest that MV and muscle conditioning work together efficiently to develop intrafusal muscle thixotropy. MV combined with hold-long conditioning may alleviate thixotropically increased muscle stiffness, such as in spastic hypertonia.