The angle subtended between the lines formed between the markers at the anterior superior iliac spine and middle of the tibiofemoral joint and that formed from the markers on the middle of the tibiofemoral joint to the middle of the ankle mortise was recorded as the valgus angle of the knee. The markers were placed on all participants by the same individual. The angle was captured at the point which corresponded to the lowest point of the landing or squat descent phase. The same individual digitized all the data from all subjects. The average FPPA angle value for both measures from three trials was used for analysis.
The test–retest reliability of this method for assessing an individual's consistency of performance of the knee valgus has been established from our laboratory and has been reported elsewhere [14]. The findings of this study showed good reliability intraclass correlation (ICC) (3,1) = 0.72 (CI (95%) = 0.58–0.89) (p < 0.001), with a smallest detectable difference (SDD) of 8.0° for SLS and ICC = 0.82 (CI (95%) = 0.68–0.9) (p < 0.001), and SDD 7.8° for SLL.