Adaptation of balance reactions following forward perturbations in people with joint hypermobility syndrome

BACKGROUND: Joint Hypermobility Syndrome (JHS) is a Heritable Disorder of Connective tissue characterised by joint laxity and chronic widespread arthralgia. People with JHS exhibit a range of other symptoms including balance problems. To explore balance further, the objective of this study is to compare responses to forward perturbations between three groups; people who are hypermobile with (JHS) and without symptoms and people with normal flexibility. METHODS: Twenty-one participants with JHS, 23 participants with Generalised Joint Hypermobility (GJH) and 22 participants who have normal flexibility (NF) stood on a platform that performed 6 sequential, sudden forward perturbations (the platform moved to the anterior to the participant). Electromyographic outcomes (EMG) and kinematics for the lower limbs were recorded using a Vicon motion capture system. Within and between group comparisons were made using Kruskal Wallis tests. RESULTS: There were no significant differences between groups in muscle onset latency. At the 1st perturbation the group with JHS had significantly longer time-to-peak amplitude than the NF group in tibialis anterior, vastus medialis, rectus femoris, vastus lateralis, and than the GJH group in the gluteus medius. The JHS group showed significantly higher cumulative joint angle (CA) than the NF group in the hip and knee at the 1st and 2nd and 6th perturbation, and in the ankle at the 2nd perturbation. Participants with JHS had significantly higher CA than the GJH group at the in the hip and knee in the 1st and 2nd perturbation. There were no significant differences in TTR. CONCLUSIONS: The JHS group were able to normalise the timing of their muscular response in relation to control groups. They were less able to normalise joint CA, which may be indicative of impaired balance control and strength, resulting in reduced stability.