Postural reactions following forward platform perturbation in young, middle-age, and old adults

The aim of the study was to examine how individuals of different ages react to forward balance perturbations. Thirty-six volunteers, divided into four groups [young (YA), middle-age (MA(40) and MA(50)), and old (OA) adults], stood on a platform that was either kept stationary, moved backward, or moved forward. EMG onset, EMG time-to-peak, iEMG, and agonist-antagonist co-activation, as well as cumulative angular excursion, maximum center of mass (CM) backward displacement, and CM time-to-reversal were assessed after forward translations. Postural synergies were assessed using principal component analysis (PCA). The results showed that OA activated their muscles later than YA [TA=25 ms, RF=17 ms] and OA and MA(50) reached the peak of activation later than YA [MA(50):TA=23 ms, RF=32 ms, OA:TA=28 ms, RF=21 ms]. Moreover, OA kept a higher level of activation longer than all younger groups. No differences among groups were observed in co-activation, kinematic, and PCA variables. We conclude that changes in temporal EMG patterns can be seen in the fifth decade. However, such changes have no effect on the CM horizontal displacement and CM time-to-reversal after perturbation, which cannot be justified by the use of different postural synergies, suggesting that temporal aspects of muscle activation could play a minor role in controlling excessive CM displacements after perturbations.