The reliability and validity of the measurement of lateral trunk motion in two-dimensional video analysis during unipodal functional screening tests in elite female athletes

Objective: To investigate the reliability and validity of the measurement of lateral trunk motion (LTM) in two-dimensional (2D) video analysis of unipodal functional screening tests.

Design: Observational study.

Setting: Research laboratory.

Participants: Forty-three injury-free female athletes.

Main outcome measures: Knee valgus (KV) and lateral trunk motion (LTM) angles were measured with a standard digital camera during the single leg squat and the single leg drop vertical jump (SLDVJ). Three-dimensional motion analysis was used during the SLDVJ to measure peak external knee abduction moment (pKAM). Intraclass correlation coefficients were calculated to assess the intra- and intertester reliability of the LTM angle. Correlations between 2D angles and pKAM were calculated for the SLDVJ.

Results: Excellent intraclass correlation coefficients for the LTM angle were found within (0.99-1.00) and between testers (0.98-0.99). The sum of KV and LTM was significantly correlated with the pKAM during the SLDVJ for the dominant (r = -0.36; p = 0.017) and non-dominant leg (r = -0.32; p = 0.034), while either angle alone was not.

Conclusions: LTM can be measured with excellent intra- and intertester reliability. The combination of KV and LTM was moderately associated with pKAM and thus including LTM may aid assessment of movement quality and injury risk.