Compensatory stepping in response to waist pulls in balance-impaired and unimpaired women

Abstract

An effective stepping response is often critical in avoiding a fall. Our objective was to study the effects of age and balance impairment on anterior and posterior compensatory stepping strategies in response to waist pull perturbations of 1-5% body weight (BW). Based on maximal unipedal stance time (UST), we tested 15 balance-impaired old (BI, UST < 10s, mean age = 76 years), 12 healthy old (O, UST>30s, mean age = 71 years), and 13 healthy young women (Y, UST >30s, mean age=23 years). Randomized anterior and posterior pulls of 1-5% body weight (BW) were applied to the waist while kinematic and kinetic recovery responses were recorded. Results show that O and BI required 0.5 more steps than Y to recover balance for posterior pulls of 4-5% BW (P < 0.01). For anterior pulls of 4-5% BW, only BI had a greater probability of step initiation (P<or=0.05 or <0.02) and mean number of steps required to recover balance (P < 0.03). The Y used 93% greater torso extension and 24% greater torso flexion in responding to anterior and posterior pulls, respectively. In the posterior, but not anterior direction, O employed smaller (P < 0.007), but more laterally-directed (P < 0.03) steps than the Y. The BI were less able to attenuate their momentum during the step landing in both directions. We conclude that the additional steps required by the BI in both directions occurred because their initial step failed to properly arrest their momentum. Controlling torso inclination before step liftoff and linear momentum after step landing are critical components of successful compensatory stepping.