Coordination Variability With External Loads

Abstract

People in the military frequently carry external loads, leading to increased joint loading. They most likely adopt strategies to minimize joint damage therefore need to vary movement patterns even with load. How external loads affect movement flexibility is unclear. PURPOSE: The purpose of this study was to determine the effect of external loads on movement flexibility while walking, represented by coupling angle variability (CAV). We hypothesized that CAV would increase across loading conditions and as people walked longer with load. METHODS: Ten participants (22 ± 1.4 years old, 1.75 ± 0.1 m, 65.30 ± 12.9 kg) walked for three 5-minute trials on a split-belt treadmill with 0%, 15%, and 30% of body mass added with a weighted vest. Kinematics were determined from motion capture (200 Hz) and Visual 3D. Segment CAV between the thigh and shank was determined for sagittal (thigh)-sagittal (shank) (sag-sag) planes, sagittal-transverse (sag-tra) planes, and frontal-frontal (fro-fro) planes with circular statistics from five strides from the first, third, and fifth minute of each condition. Differences in CAV were analyzed via 2-way repeated measures ANOVA. RESULTS: Sag-sag CAV increased 2.16% (p < 0.001), Sag-tra CAV increased 2.87% (p < 0.001), and Fro-fro CAV increased 4.31% (p < 0.001) across the loads. The amount of time walking during the 5-minute trial did not significantly affect CAV (p-values 0.867 - 0.960). DISCUSSION: Participants increased CAV with increasing loads across the three segment couples throughout the 5-minute walking trial. More CAV may allow for better load accommodation through increased movement adaptability. Segments that can vary patterns while walking can self-optimize for loading and potentially avoid joint damage. Our young, healthy participants walked for short periods of time on a treadmill for each condition, which may not represent the movement flexibility in people carrying loads for long duration over challenging terrain.