Variability in the Center of Mass State During Initiation of Accurate Forward Step Aimed at Targets of Different Sizes

Motor control for forward step initiation begins with anticipatory postural adjustments (APAs). During APAs, the central nervous system controls the center of pressure (CoP) to generate an appropriate center of mass (CoM) position and velocity for various task requirements. In this study, we investigated the effect of required stepping accuracy on the CoM and CoP parameters during APA for a step initiation task. Sixteen healthy young participants stepped forward onto the targets on the ground as soon as and as fast as possible in response to visual stimuli. Two target sizes (small: 2 cm square and large: 10 cm square) and two target distances (short: 20% and long: 40% of the body height) were tested. CoP displacement during the APA and the CoM position, velocity, and extrapolated CoM at the timing of the takeoff of the lead leg were compared among the conditions. In the small condition, comparing with the large condition, the CoM position was set closer to the stance limb side during the APA, which was confirmed by the location of the extrapolated center of mass at the instance of the takeoff of the lead leg [small: 0.09 ± 0.01 m, large: 0.06 ± 0.01 m, mean and standard deviation, F(1, 15) = 96.46, p < 0.001, η2 = 0.87]. The variability in the mediolateral extrapolated center of mass location was smaller in the small target condition than large target condition when the target distance was long [small: 0.010 ± 0.002 m, large: 0.013 ± 0.004 m, t(15) = 3.8, p = 0.002, d = 0.96]. These findings showed that in the step initiation task, the CoM state and its variability were task-relevantly determined during the APA in accordance with the required stepping accuracy.

Downward Gazing for Steadiness

When walking on an uneven surface or complex terrain, humans tend to gaze downward. Previous investigations indicate that visual information can be used for online control of stepping. Behavioral investigations suggest that, during walking, the availability of visual information increases stepping accuracy, but probably through a feedforward control mechanism. Consequently, downward gazing (DWG) is usually interpreted as a strategy used to acquire useful information for online and/or feedforward control of stepping.Visual information is not exclusively used for guiding locomotion; a wealth of literature has been published on the usefulness of visual information for feedback postural control. Critically, postural control has been shown to be sensitive to the visual flow arising from the respective motion of the individual and the 3D environment.To investigate whether DWG can be used to enhance feedback control of posture, rather than feedforward/online control of gait, we conducted a series of experiments that explore this possible interplay. Through these experiments we were able to show that DWG, just a few steps ahead, results in a steadier standing and walking posture, without the need for accuracy. Moreover, we were able to demonstrate that humans resort to DWG when walking stability is compromised, even when destabilizing features were visually unpredictable.This series of experiments provides sufficient evidence of the possible interplay between visual information used for guiding locomotion and that used for postural control. Moreover, this evidence raises concerns regarding the way we interpret gaze behavior without the knowledge of the type and use of the information gathered.

134 Reliability and Usability of Step Sensing System on Gait Speed and Stepping Accuracy Measurement: A Preliminary Evaluation

Background Falls are the most common cause of injury among older people in Thailand. However, there are no established falls prevention programs in our community. Telehealth is one of the strategies to overcome this unmet need. We have developed the Step Sensing System (SSS) for measuring gait speed and stepping accuracy of multi target stepping task (MTST). This system comprises of the footstep sensing modules, controller box and analyzing computer. SSS records each footfall and compares with an assignment for each walking trail. The results will be sent to a cloud storage which are accessible by web-based and mobile applications. By using this technology, we are able to remotely access falls risk and monitor MTST performance in older people. Methods We placed footstep sensing modules under a 6-metre mat, then asked a 32-year-old healthy woman to walk across the mat for 4 trails: usual-pace, faster-pace, usual-pace with 1 assigned target and usual-pace with 2 assigned targets on an alternating sequence. We evaluated the system reliability by comparing gait speed and stepping accuracy on 3rd and 4th trails with video recorded by Intel RealsenseTM Depth Camera (model D415). Results SSS and video recording has excellent correlation for gait speed and stepping accuracy measurement (intraclass correlation coefficient [ICC] > 0.99, p value < 0.001). The user satisfaction measured by the System Usability Scale was 70/100. Conclusions SSS demonstrated promising results on gait speed and stepping accuracy measurement in controlled environment. For the next step, we plan to increase ability of gait measurement on various parameters and perform the validity assessment in community setting.

The Effects of a Divided-Attention Timed Stepping Accuracy Task on Balance, Strength, Endurance, and Functional Performance in Healthy Older Adults: A Pilot Study

The aim of this study was to investigate whether a 6-week Divided-Attention Stepping Accuracy Task (DATSAT) intervention improved the primary outcome measure, maximal step length; other balance measures (Berg Balance scale and Timed Up and Go test); leg strength; endurance (6-min walk test); and functional tasks in 15 community-dwelling healthy older adults (age: 71.5 years, female: 46.7%) compared with 15 community-dwelling healthy older adults in a Bike and Strength (B&S) program (age: 73.8 years, female: 33.3%). Participants trained 3× per week, 30–60 min per session. Stepping-group differences were significant for all measures. B&S group improved in maximal step length (anterior and lateral), strength, and one functional task. Stepping group outperformed B&S group in Timed Up and Go and maximal step length posterior. B&S group outperformed stepping group in two strength measures. Exertion scores were lower for the stepping group. Overall, Divided-Attention Timed Stepping Accuracy Task training resulted in more within-group improvements and two between-group measures with less perceived effort and shorter intervention times.