Abstract
This study examined the effects of muscle tendon vibration on a kinesthetic targeting task in one and two-dimensional movements. Tendon vibration of lengthening muscles creates an illusion of increased muscle length, causing undershooting in target-directed reaching. While dual agonist/antagonist vibration has been suggested to degrade proprioception, its impact on target directed movements is unclear. 30 participants performed either a one-dimensional elbow extension or a two-dimensional wrist motion task under four vibration conditions: flexor, extensor, dual flexor/extensor, and no vibration. In the elbow task, flexor vibration led to undershooting, while extensor vibration caused overshooting. The effects of vibration in the two-dimensional task depended on the movement, with illusions being strongest when the vibrated muscle acted as the antagonist and disappearing when acting as the agonist. Surprisingly, dual vibration did not increase variable error, suggesting it did not degrade proprioception. The results may suggest that the effects of tendon vibration depend on the reliability of afferent signals from the muscle. When the muscle is being rapidly shortened (unloads muscle spindles), the afferent signal is less reliable, resulting in no kinesthetic illusion. In the case of the elbow-extension task, the movement may have been slow enough that the agonist was not fully unloaded, resulting in a small illusion. Overall, our results demonstrate that vibration-induced kinesthetic illusions can be used to perturb both one and two-dimensional movements, and that the size of the illusion is influenced by the reliability of the afferent feedback coming from the muscle.
