Age associated differences in postural equilibrium control: a comparison between EQscore and minimum time to contact (TTC(min)).

Increased postural instability and the subsequent elevation in fall incidence with increasing age are important contributors for hip fractures and developing frailty. When testing for such instability, most studies characterize balance in terms of center-of-mass (COM) deviation from a finite point, the "equilibrium point", located at the center of a subject's stance. For example, the clinically accepted equilibrium score (EQscore) represents instability as the maximum peak-to-peak sway about the "equilibrium point". An alternative theory views balance as being controlled within a "stability margin" in which all corrective actions are based on the time to contact (TTC) of the body's COM with that margin. This study examines the differences offered by evaluating balance control using the EQscore and TTC approach across several age groups and sessions. Consenting subjects from the Baltimore Longitudinal Study of Aging were recruited (N=155) from each age decade (20s-80s) who were generally healthy and free from neurological diagnoses. Results showed TTC tests detected significant variations in eyes open versus eyes closed testing that were unpredictable by EQscore. Further, TTC produced differences in age-related stability threats not seen using EQscore. The TTC data also provided a discriminating difference between subjects who fell in the difficult tests and those who maintained posture. Overall, these data suggest EQscore might not sufficiently account for dynamic control components the body may be using to maintain balance. TTC may offer a more accurate estimate of postural stability (functional ability) than EQscore based on its inclusion of a velocity component to detect dynamic changes.