Adaptation of the Compensatory Stepping Response Following Predictable and Unpredictable Perturbation Training

BackgroundEffective training of the backward step response could be beneficial to improve postural stability and prevent falls. Unpredicted perturbation-based balance training (PBT), widely known as compensatory-step training, may enhance the fear of falling and the patterns of postural muscle co-contraction. Contrastingly, PBT with predictable direction or both direction and timing would suppress the fear and the co-contraction patterns during training, but the efficacy of predictable PBT for unpredictable perturbations is still unknown.ObjectiveTo compare the adaptation effects of compensatory-step training with and without predictable perturbations on backward stepping against unpredictable perturbations.MethodsThirty-three healthy young adults were randomly assigned to one of the following step training groups: Unpredicted, Predicted, and Self-initiated. In training sessions, participants were perturbed to induce a compensatory step with (Predicted group) or without (Unpredicted group) knowledge of the perturbation’s direction or while knowing both the direction and timing of the perturbation (Self-initiated group). In test sessions (pre- and post-training), participants were instructed to recover their postural stability in response to an unpredicted perturbation. The margin of stability (MOS), center of mass (COM) shift, and step characteristics were measured during a backward step in both test and training sessions.ResultsAll three groups showed a significant increase in the step length and velocity in the post-training sessions compared to those in the pre-training sessions. Moreover, in the Unpredicted and Predicted groups, but not in the Self-initiated group, the MOS at step contact was significantly increased following the training session. In addition, the Self-initiated group showed a significant increase in COM shift at 50 ms after slip onset during training compared to the Unpredicted and Predicted groups.ConclusionUnpredicted and predicted PBT improve step characteristics during backward stepping against unpredictable perturbations. Moreover, the unpredictable PBT and PBT with direction-predictable perturbations enhance the feedback postural control reflected as the postural stability at step contact.

Ankle motor strategy use in older and younger adults as assessed by a two-dimensional kinematic analysis smart device application

Background/aims Motor strategies change with age, resulting in balance deficits. Clinical options for objectively measuring motor strategies are limited. The use of two-dimensional kinematic analysis through smart devices and applications may provide a cost-effective portable solution for measuring differences in motor strategy use between older and younger adults. The aims of this study were to investigate the concurrent validity of a two-dimensional software and two-dimensional application and to determine whether the application could capture the difference in ankle motor strategy use by older and younger adults (construct validity). Methods Video clips captured by Sony and iPad Air cameras were used to assess concurrent validity between the two-dimensional software and application. A total of 30 older (72.6 ± 4.0 years) and 30 younger (26.5±4.5 years) adults performed forward and backward stepping. A two-dimensional applicationmeasured the ankle position in degrees and time taken in seconds to initiate and complete a compensatory step. Results The two-dimensional software and app demonstrated excellent reliability (ICC2,1 ≥0.994). The ankle forward stop angle differed significantly between older and younger adults (P=0.012). No differences were observed in time taken to initiate and complete a compensatory step. Conclusions The two-dimensional application appears to be a valid alternative to two-dimensional software for measuring ankle motor strategies. Further investigation for clinical use is warranted.