Criterion validity of 3D trunk accelerations to assess external work and power in able-bodied gait.

Evaluative quantification of gait disorder minimizing time-consuming and cost-intensive laboratory installations remains a challenging task in movement analysis. We examined the criterion validity of global gait mechanics assessed by trunk accelerometry. Eight female and four male volunteer subjects (mean age, 27.5 years; S.D., 5.1 years; weight, 68.7+/-11.3kg; height, 1.74+/-0.08m) without gait dysfunction participated in the study. They walked barefoot over two adjacent force-platforms at self-selected speeds. In addition to ground reaction forces, vertical, anterior-posterior and medio-lateral accelerations of the trunk were simultaneously measured by means of a light tri-axial accelerometer. Mean acceleration cycles of the trunk and the body centre of mass were calculated. Acceleration vectors were integrated twice to obtain velocity and displacement vectors of the trunk and the centre of mass, respectively. Temporal boundaries of right and left functional stance phases were defined by the two intermediate moments between maximum anterior-posterior velocity and minimal vertical displacement. Cross-correlations of the kinematics of the trunk and the centre of mass were determined. External work and corresponding symmetry indicators were computed for both methods. Centre of mass anterior-posterior displacement lagged behind the trunk by 3.5% of the gait cycle. External power correlated highly (r>0.82) between the trunk model and the centre of mass. Work correlated moderately high (r=0.77) between the two methods. Work and power asymmetry indexes correlated moderately high (r>0.64). Our findings suggest that accelerometry has the potential to assess functional kinematics and energy-related outcomes in large cohorts.