Validity and reliability of IMUs-based system in assessing lower extremity inter-joint coupling angles and...

To validate an inertial measurement unit (IMUs)-based system for quantifying lower extremity inter-joint coordination during gait in older adults.

45 older adults performed multi-speed walking trials with simultaneous IMUs and optical motion capture (OMC) derived-measurements. Hip, knee, and ankle joint angles were used to compute coupling angles (CAs), coupling angle variability (CAV) and coordination patterns for four joint pairs using the modified vector coding technique. Validity and reliability were evaluated using the coefficient of multiple correlation (CMC) and systematic error (SE) for CA waveforms, and Spearman correlations for CAV.

IMUs-derived coupling angles demonstrated excellent waveform agreement with OMC after offset correction (coefficients of multiple correlation [CMCs]: 0.944-0.978), with greater SE reductions observed in proximal joint pairs (hip sagittal-knee sagittal [HsKs]) than distal pairs (knee sagittal-ankle sagittal [KsAs]). Coupling angle variability (CAV) parameters showed moderate-to-strong correlations with OMC (average r_s ≥ 0.6), particularly during slow walking (average r_s = 0.682) and late stance phase (r_s = 0.535-0.826). Reliability analysis indicated strong waveform consistency (within-rater CMC: 0.940-0.981; between-rater CMC: 0.954-0.988), with lower SE for HsKs (15.6°-20.6°) than KsAs (31.8°-39.3°). For CAV, higher reliability was found in hip sagittal-ankle sagittal (HsAs) (r_s = 0.747/0.725) compared to KsAs (r_s = 0.554/0.651), and slow walking yielded the best reproducibility (r_s = 0.661/0.683).

These findings supported the IMUs-based system as a valid and reliable tool for assessing inter-joint sagittal coordination in older adults, with performance affected by joint coupling pairs and gait speed.