Objectives:To test the construct validity of the modified Star Excursion Balance Test (SEBT) in predicting the strength of knee extensors and hip abductors and to compare performance between dominant and non-dominant legs.Strength, as measured using hand held dynamometry, has been used as one of a variety of measures in order to subgroup patients with patellofemoral pain. This method is not well received in clinical practice due to time constraints and cost. In contrast, the SEBT is a quick and simple functional measure of dynamic stability. This study examined the validity of the SEBT as an alternate strength measure.Design: Within subject correlation. Each participant recorded maximum isometric contractions for hip abduction and knee extension using a HHD and performed the modified SEBT, on both legs, within one test period. Paired t tests were used to compare dominant and non-dominant legs and Pearson's correlation analyses were used to explore for associations. Setting: Non-clinical environment,Participants: Eighteen healthy male amateur runner's between 18 and 39 years old (mean age 36.1 years). Main outcome measures:Knee and hip moments normalised for leg length (Nm/m) for the HHD and percent of leg length reach score for each SEBT reach as well as a composite of all three.Results: There was no significant difference between dominant and non-dominant legs for all the tests (knee extension p = 0.72, hip abduction p = 0.90, SEBT composite p = 0.86) therefore data was combined into one set. There was no significant relationship between either hip abduction strength (r = 0.28, p = 0.11), or knee extension strength (r= 0.16, p = 0.17), with any combination of the SEBT. A moderate relationship (r = 0.52, p = 0.38) between hip abduction and SEBT posterolateral reach was seen, however, this was not statistically significant. Conclusion:There was no statistically significant association between either knee extension or hip abduction strength with the modified SEBT. This suggests that strength is unlikely to be a primary construct of the test and the SEBT is not a useful replacement for the HHD when testing strength.