Validity of the four-square step test in persons with haemophilia.

FSST is a valid and safe measure to use in PWH. It correlates strongly with other functional measures, has excellent inter and intra rater reliability. FSST correlates with age rather than severity type and provides information to the clinician on the speed/ability to change direction and clear an obstacle. ABC questionnaire was able to differentiate between severities and offers insight into patient confidence to move. SPPB had a ceiling effect with 52/80 scoring 12 and may not be suitable for PWH.