Variation between individuals in sensorimotor feedback control of standing balance

We examined intersubject variation in human balance, focusing on sensorimotor feedback. Our central hypothesis was that inter subject variation in balance characteristics arises from differences in central sensorimotor processing. Our second hypothesis was that similar sensorimotor feedback mechanisms are used for sagittal and frontal balance. Twenty-one adults stood on a continuously rotating platform with their eyes closed in the sagittal or frontal plane. Plant dynamics (mass, height, and inertia) and feedback control were included in a model of sensory weight, neural time delays, and sensory-to-motor scaling (stiffness, damping, and integral gains). Sway metrics [root-mean-square (RMS) sway and velocity] were moderately correlated between planes of motion (RMS: R = 0.66-0.69 and RMS velocity: R = 0.53-0.58). Sensory weight and integral gain exhibited the highest correlations between the plane of motion (R = 0.59 for sensory weight and R = 0.75 for integral gain during large stimuli). Compared with other subjects, people who adopted a high vestibular weight or large integral gain in one condition did so across all tests. Intersubject variation in sensory weight, stiffness, and integral gain were significantly associated with intersubject variation in RMS sway whereas sensory weight and time delay were the strongest significant predictors of RMS velocity. Multiple linear regression showed that intersubject variation in sway metrics was predicted better by intersubject variation in central feedback mechanisms vs. plant dynamics. Together, results supported the first hypothesis and partially supported the second hypothesis because only a subset of feedback processes was moderately or strongly correlated (mostly during large surface tilts) between planes of motion.