title: Kinematics of the threshold of balance recovery are not affected by instructions limiting the number of steps in younger adults.
abstract: To our knowledge, the effect of instructions limiting the number of steps on the threshold of balance recovery has not been quantified, which could make comparisons between studies difficult. We determined the maximum forward lean angles from which 28 younger adults could be suddenly released and still recover balance using: (i) only a single step, (ii) no more than two steps and (iii) no limit on the number of steps. Results showed that instructions limiting the number of steps significantly affected the maximum lean angle but only by a maximum of 1 degree. At the maximum lean angles, they also significantly affected reaction time, first weight transfer time, first stride velocity, first stride length and second stride velocity but only by 8% on average. However, they did not affect muscular latencies, first stride time, first stride height, first stride width or other second step variables. Moreover, at lean angles larger than their maximum, participants were able to respect the instructions but unable to recover balance without safety harness assistance. Given that the effect was too small to be pertinent, we can state that, between the three limits on the number of steps, not only were the maximum lean angles similar but the first steps were nearly identical and the additional steps did not help to increase the maximum lean angle. Therefore, we have demonstrated that instructions limiting or not limiting the number of steps appear to be equally valid to study the threshold of balance recovery in younger adults.
authors.affiliation: Research Center on Aging, 1036 rue Belvédère Sud, Sherbrooke, QC J1H 4C4, Canada.
authors.forename: Marc-André
authors.initials: MA
authors.lastname: Cyr
authors.forename: Cécile
authors.initials: C
authors.lastname: Smeesters
mesh_terms: D000704:Analysis of Variance; D001696:Biomechanical Phenomena; D004576:Electromyography; D005260:Female; D006801:Humans; D007700:Kinetics; D007866:Leg / Q000502:physiology*; D008297:Male; D018482:Muscle, Skeletal / Q000502:physiology; D004856:Postural Balance / Q000502:physiology*; D016138:Walking / Q000502:physiology*; D055815:Young Adult