Age and cognitive load affect muscle activation profiles in response to physical perturbations while walking

To maintain balance during walking, the central nervous system must adjust the base of support (i.e., modulation of step length and step width) to the center of mass displacement in every step. We aimed to explore age and concurrent cognitive attention-demanding task effects on lower limb muscle fiber type recruitment in response to unexpected loss of balance during walking i.e., perturbation. Twenty young (YA) and 18 older adults (OA), (27.00{+/-}2.79 and 70.13{+/-}3.95 years old, respectively) were exposed to unexpected perturbations, while walking on a treadmill, in virtual reality environment. Surface electromyography (sEMG) total spectral power for frequency bands associated with muscle fibers type I (40-60Hz), type IIa (60-150Hz) and type IIb (150-250Hz), from tibialis-anterior and vastus-lateralis muscles were analyzed. Four Generalized Estimating Equations models assessed age and cognitive attention-demanding tasks load association with lower-limb muscle activation patterns resulting from perturbation in single- and double-support phases of the gait cycle. Results show that OA employ a muscle fiber type IIa dominant increase strategy while YA show muscle fiber type IIb dominant increase in muscle fiber type recruitment in response to unexpected perturbations during walking. This suggests that the ability to recruit fast-twitch muscle fibers is deteriorated with age and thus may be related to insufficient balance recovery response.