Reliability and validity of modified Four Square Step Test (mFSST) performance in individuals with Parkinson’s disease

Parkinson's disease (PD) is a complex disorder marked with non-motor and motor impairments, including gait abnormalities and postural instability. As a result of balance dysfunction and postural instability, falls and injuries are common composite impairments of PD. The modified Four Square Step Test (mFSST) replaces the canes utilized in the traditional Four Square Step Test (FSST) with tape to evaluate dynamic standing balance while stepping in multiple directions.Determine the reliability and validity of the mFSST in individuals with PD.Twenty-seven participants diagnosed with PD on medication H&Y I-III, mean age 73.07 ± 6.4, completed the FSST and mFSST. Participants performed both assessments two times using the fastest time for interrater reliability and concurrent validity. To determine the test-retest reliability, participants performed the mFSST again 20-60 min following initial assessment.The interrater and test-retest reliability was excellent (r = 0.916-0.999, ICC2,2 = 0.96-0.99). The mFSST and FSST were highly correlated for concurrent validity (r = 0.823, p < .01).The mFSST demonstrates excellent reliability and validity while assessing dynamic standing balance in individuals with PD. The mFSST can be completed while requiring little equipment, space, and time in multiple rehabilitation settings.