Effect of Achilles tendon vibration on posture in children

This study investigated the effect of unilateral Achilles tendon vibration on postural response in children and young adults during standing. Thirty healthy subjects participated in this study including ten 6-year-old children (YC group), ten 10-year-old children (OC group), and ten young adults (YA group). Eight-second vibration was elicited in each trial from a small vibrator attached above the right Achilles tendon when participants stood barefoot on a force platform. Three 40-s trials were collected under both eyes-open and eyes-closed conditions. Center of pressure (COP) was calculated to examine postural response during the pre-vibration, vibration and post-vibration phases. Results show that both the YC and OC groups had a greater COP average velocity than the YA group in all three phases. Tendon vibration induced a directionally specific postural response in all three groups such that the onset of vibration induced a posterior and medial COP shift during the vibration phase, and the offset of vibration induced an anterior and lateral COP shift during the post-vibration phase. Timing of the maximal COP shift was comparable among three groups in both anterior-posterior (AP) and medial-lateral (ML) directions. However, only the OC group showed an adult-like magnitude of the maximal COP shift during the post-vibration phase in the AP direction. These results suggest that 6-year-old children may start showing an adult-like directionally specific response and temporal parameter to tendon vibration during standing; however, the development of an adult-like spatial postural response to tendon vibration may take more than 10 years.