Damping control of balance in the medial/lateral direction and the risk of falling in the elderly.

Aims: A proportional-integral-derivative (PID) control has recently been used as a control algorithm of body balance. The purpose of this study was to elucidate an association of the proportional and derivative gain based on the PID control gain for balance for quiet standing with the risk factor for falls in the elderly.

Methods: The movement of a marker on the back of 23 elderly participants (age 75.6±6.6 years) was measured by our developed device with a complementary metal oxide semiconductor video camera and the trunk sway speed in the medial/lateral (M/L) direction (TSSX) was calculated as absolute values of the whole time series. The PID control gain (proportional gain: K(P), integral gain: K(I), derivative gain: K(D)) was identified using the trunk sway data, and normalized by individual height and weight (K(P)n, K(D)n and K(I)n). Individual risk factor for falls was additionally assessed with the Tinetti Performance Oriented Mobility Assessment (POMA) and the fall risk questionnaire.

Results: The score in the POMA and the K(D)n significantly decreased with age (P<0.01). The score in the POMA showed a positive correlation with the K(D)n, and negative correlations with the TSSX and K(P)/K(D) ratios (P<0.01). The average K(D)n and the score in the POMA of fallers were significantly lower than those of non-fallers (P<0.05).

Conclusion: These results suggest that the decreased damping control by derivative gain for balance in the M/L direction is one of the risk factors for falls in the elderly.