Using relative phase analyses and vector coding to quantify Pelvis-Thorax coordination during lifting-A methodological investigation.

Low-back disorder risk can be modulated by pelvis-thorax coordination when lifting. To objectively discriminate between coordination patterns during lifting, the analytical methods used require evaluation. The primary study objective was to determine if continuous relative phase (CRP) and vector coding (VC) analyses can discriminate between lifting techniques that differ based on biomechanical risk criteria. The secondary objective was to determine if normalization/transformation of input segmental angular position and velocity data is required to discriminate between lifting techniques. Sixteen volunteers performed a sagittal lifting task using freestyle (FRE), flexed spine (FLX), and neutral spine (NTL) techniques. CRP and VC analyses were implemented to quantify pelvis-thorax coordination patterns based on time-normalized, phase-normalized, and Hilbert-transformed segmental angular kinematic data. Mean relative phase angles along with thorax-only and in-phase coupling patterns were significantly different between FRE-NTL and FLX-NTL techniques (p < 0.01), but not FRE-FLX (p > 0.44). This finding was consistent across all relative phase normalization/transformation methods. Therefore, CRP and VC analyses successfully discriminated between different lifting techniques, regardless of the relative phase normalization/transformation method used.