Age differences in processing fluctuations in postural control across trials and across days.

Postural control performances of 18 younger and 18 older adults were repeatedly measured on 45 weekdays with five trials per day. This design made it possible to dissociate between long-term trends and processing fluctuations in the sensorimotor domain at moment-to-moment, trial-to-trial, and day-to-day levels. Older adults fluctuated more than younger adults at all timescales. Age differences in trial-to-trial and day-to-day processing fluctuations were reduced but remained statistically significant when controlling for fluctuations on faster timescales. We concluded that age differences in intraindividual fluctuations at the longer timescales are in part related to age differences in low-level system robustness, suggesting a cascade of effects across multiple timescales.