Aging effects of motor prediction on protective balance and startle responses to sudden drop perturbations

This pilot study investigated the effect of age on the ability of motor prediction during self-triggered drop perturbations (SLF) to modulate startle-like first trial response (FTR) magnitude during externally-triggered (EXT) drop perturbations. Ten healthy older (71.4 ± 1.44 years) and younger adults (26.2 ± 1.63 years) stood atop a moveable platform and received blocks of twelve consecutive EXT and SLF drop perturbations. Following the last SLF trial, participants received an additional EXT trial spaced 20 min apart to assess retention (EXT RTN) of any modulation effects. Electromyographic (EMG) activity was recorded bilaterally over the sternocleidomastoid (SCM), vastus lateralis (VL), biceps femoris (BF), medial gastrocnemius (MG), and tibialis anterior (TA). Whole-body kinematics and kinetic data were recorded. Stability in the antero-posterior direction was quantified using the margin of stability (MoS). Compared with EXT trials, both groups reduced SCM peak amplitude responses during SLF and EXT RTN trials. VL/BF and TA/MG coactivation were reduced during SLF FTR compared to EXT FTR (p < 0.05) with reduced peak vertical ground reaction forces (vGRF) in both younger and older adults (p < 0.05). Older adults increased their MoS during SLF FTR compared to EXT FTR (p < 0.05). Both groups performed more eccentric work during SLF trials compared to EXT (p < 0.05). These findings indicate that abnormal startle effects with aging may interfere with balance recovery and increase risk of injury with external balance perturbations. Motor prediction may be used to acutely mitigate abnormal startle/postural responses with aging.