Postural stabilization during bilateral and unilateral vibration of ankle muscles in the sagittal and frontal planes

Background: The purpose was to investigate the postural consequences of proprioceptive perturbation of the Triceps Surae and Peroneus Longus muscles. These muscles are known to control posture respectively in the sagittal and frontal planes during standing. Methods: Standard parameters and the time course of center of pressure (CoP) displacements were recorded in 21 young adults, instructed to maintain their balance during tendon vibration. Following 4 s of baseline recording, three types of vibration (80 Hz) were applied for 20 s each on the Peroneus or Achilles tendons, either unilaterally or bilaterally (with eyes shut). The recording continued for a further 24 s after the end of the vibration during the re-stabilization phase. To evaluate the time course of the CoP displacement, each phase of the trial was divided into periods of 4 seconds. Differences between the type of tendon vibration, phases and periods were analyzed using ANOVA. Results: During all tendon vibrations, the speed of the CoP increased and a posterior displacement occurred. These changes were greater during Achilles than during Peroneus vibration for each type of vibration and also during bilateral compared with unilateral vibration. All maximal posterior positions occurred at a similar instant (between 12.7 and 14 s of vibration). Only unilateral Achilles vibration led to a significant medio-lateral displacement compared to the initial state. Conclusions: The effect of the proprioceptive perturbation seems to be influenced by the position of the vibrated muscle according to the planes of the musculoskeletal postural organization. The amplitude of the destabilization may be related to the importance of the muscle for postural control. The medial CoP displacement which occurred during unilateral Achilles vibration is not a general reaction to a single-limb perturbation. Proprioceptive input from the non-perturbed leg was not sufficient for the antero-posterior displacement to be avoided; however, it helped to gain stability over time. The non-perturbed limb clearly plays an important role in the restoration of the postural referential, both during and immediately following the end of the vibration. The results demonstrated that at least 16 s of vibration are necessary to induce most postural effects in young adults.