Instability training, assessing the impact of level of difficulty on balance: A randomized clinical trial

•Instability training (IT) is effective for improving balance.•The level of difficulty of IT is not indicative of balance improvements.•IT may be an additional or alternative method to train balance on stable ground. Most human movements are executed while in a state of postural instability. For this reason, instability training is a highly-specific method that is intended to improve balance and postural control. This research aimed to determine the effect of instability training on the balance of individuals with similar baseline abilities, who initiated training within different stability conditions. Does the level of difficulty with which instability training is performed determine improvements in balance? A two-arm randomized trial was undertaken, for which 22 and 21 participants were included in the experimental and control groups, respectively. The experimental group performed balance training on unstable surfaces and the control group implemented the same training on stable ground. The primary outcome was the Y-Balance Test (YBT); the Emery test, Functional Reach test, and platform measures were the secondary outcomes. Confidence intervals were set at 95% and Cohen’s f statistic was used to estimate effect size. Dynamic balance, as measured by the YBT, showed significant Time improvements in both groups for right (p