Validity of the four square step test to assess dynamic balance, step velocity and displacement

The four square step test (FSST) is commonly used to assess dynamic standing balance in elderly adult populations. To date, only the time (recorded by a stop-watch) to complete the test has been used. Other important dynamic balance information such as step velocity and step displacement can be extracted. This study re-examined the validity of recording the FSST time with a stop-watch by comparing it to a "gold standard" method (Vicon) and investigated the relationship between FSST stop-watch time and measures of step velocity, step displacement, and age. After familiarization, fourty-one healthy adults (42 ± 12 yrs.) completed three FSST trials. The FSST time was recorded by a stop-watch and the participants' foot movements were simultaneously recorded by a Vicon motion system (120 Hz). Measures extracted from the Vicon system were FSST time, step velocity (four directions) and step displacement (four directions). A paired t-test was used to compare FSST time recorded by each system. Pearson's correlation analyses were conducted to identify relationships between measures. No significant difference was found between the FSST time recorded by the methods (mean differ-ence = 0.02 ± 0.11 s). Moreover, a strong positive linear rela-tionship (r = 0.99, p < 0.0001) was found between the FSST time recorded by the methods. A moderate linear relationship was found between the FSST time (Vicon) and step velocity (r = 0.67, p < 0.0001). Poor linear relationships were found be-tween (1) step velocity and step displacement, (2) FSST time (Vicon) and step displacement, (3) FSST time (both methods) and age, (4) age and step velocity, and (5) age and step dis-placement. In conclusion, the FSST stop-watch method is valid. Moreover, it may be used to predict step velocity but not step displacement. No relationship was found between age and the FSST time, step velocity or step displacement