REAL-TIME BACKWARD SLIP DETECTION USING A SLIP-INDUCING SYSTEM AND MACHINE LEARNING METHODS

Wearable devices have been developed to assist walking based on the wearer’s intention. However, it would be dangerous if a device misidentifies falling as intentional motion; it is necessary to detect falls in real time. In particular, backward slip is the most common and dangerous type of falls. Fifteen participants walked on a split-belt instrumented treadmill while random backward slip perturbation of belt speed acceleration was provided to the foot. We aimed to identify slip within 0.35s after the onset of the perturbation, the typical window of slip, using lower limb kinematic data obtained within 0.3s; only 0.05s was allowed for the identification. We developed 5 machine learning models, and the logistic regression model showed the highest accuracy of 87.5%. The initial study is expected to contribute to the prevention of falls by developing and applying the results to wearable devices

ACUTE EFFECTS OF SHOE CONDITIONS ON FOOT STRIKE PATTERN OF RUNNERS WITH DIFFERENT HABITUAL PATTERNS

Multiple influential studies argued that minimal footwear promotes forefoot running whereas cushioned footwear promotes rear foot strike. We readdressed effects of footwear on the foot strike pattern considering runners’ habitual patterns. Based on the observed foot strike angle, we divided 9 participants into rearfoot, midfoot and forefoot runners. All participants then ran wearing 3 different shoes: performance-boosting shoes, conventional shoes, and minimal shoes. We found a significant effect of shoes on foot strike angle and the interaction between the group and shoes. Contrary to previous studies\u27 well-accepted arguments, performance-boosting shoes with thick outsoles induced the rearfoot group to run with decreased foot strike angle more effectively than minimal shoes. Our finding also revealed the hitherto seldom investigated effect of habitual patterns on adaptability

REAL-TIME PREDICTION OF FAILURE IN RESISTANCE TRAINING: APPLICATION TO ARM CURL

Resistance training has recently become popular. If failure points, beyond which the intended motion cannot be executed, are reliably predicted, it is possible to increase the efficacy of the training and decrease the risk of injury. We aim to develop machine learning models that can enhance training effects through the proper setting of the rate of perceived exertion and prevent injuries from excessive motion by predicting the failure points. Ten young and healthy adults performed 3 sets of dumbbell arm curl using each arm with a weight of 70% of their one-repetition maximum until they reached the failure point and could not perform the standard arm curl. Using the kinematic features that we collected during each set, we developed failure prediction models based on five classification algorithms. Four models out of the five yielded the accuracy over 90%. Our findings suggest that these models can enhance the training effects by maintaining proper rate of perceived exertion, and prevent injuries due to excessive training load

Walking Is Not Like Reaching: Evidence from Periodic Mechanical Perturbations

The control architecture underlying human reaching has been established, at least in broad outline. However, despite extensive research, the control architecture underlying human locomotion remains unclear. Some studies show evidence of high-level control focused on lower-limb trajectories; others suggest that nonlinear oscillators such as lower-level rhythmic central pattern generators (CPGs) play a significant role. To resolve this ambiguity, we reasoned that if a nonlinear oscillator contributes to locomotor control, human walking should exhibit dynamic entrainment to periodic mechanical perturbation; entrainment is a distinctive behavior of nonlinear oscillators. Here we present the first behavioral evidence that nonlinear neuro-mechanical oscillators contribute to the production of human walking, albeit weakly. As unimpaired human subjects walked at constant speed, we applied periodic torque pulses to the ankle at periods different from their preferred cadence. The gait period of 18 out of 19 subjects entrained to this mechanical perturbation, converging to match that of the perturbation. Significantly, entrainment occurred only if the perturbation period was close to subjects' preferred walking cadence: it exhibited a narrow basin of entrainment. Further, regardless of the phase within the walking cycle at which perturbation was initiated, subjects' gait synchronized or phase-locked with the mechanical perturbation at a phase of gait where it assisted propulsion. These results were affected neither by auditory feedback nor by a distractor task. However, the convergence to phase-locking was slow. These characteristics indicate that nonlinear neuro-mechanical oscillators make at most a modest contribution to human walking. Our results suggest that human locomotor control is not organized as in reaching to meet a predominantly kinematic specification, but is hierarchically organized with a semi-autonomous peripheral oscillator operating under episodic supervisory control.New York State Spinal Cord Injury Center of Research Excellence (contract CO19772)Massachusetts Institute of Technology. Eric P. and Evelyn E. Newman Laboratory for Biomechanics and Human RehabilitationSamsung Scholarship Foundatio

Improved Assessment of Orbital Stability of Rhythmic Motion with Noise

Mathematical techniques have provided tools to quantify the stability of rhythmic movements of humans and machines as well as mathematical models. One archetypal example is the use of Floquet multipliers: assuming periodic motion to be a limit-cycle of a nonlinear oscillator, local stability has been assessed by evaluating the rate of convergence to the limit-cycle. However, the accuracy of the assessment in experiments is questionable: Floquet multipliers provide a measure of orbital stability for deterministic systems, but various components of biological systems and machines involve inevitable noise. In this study, we show that the conventional estimate of orbital stability, which depends on regression, has bias in the presence of noise. We quantify the bias, and devise a new method to estimate orbital stability more accurately. Compared with previous methods, our method substantially reduces the bias, providing acceptable estimates of orbital stability with an order-of-magnitude fewer cycles

A PILOT STUDY ASSESSING EFFECTS OF TAPING THE ANKLE TENDONS ON POSTURAL CONTROL UNDER UNPREDICTABLE PERTURBATION

Unpredictable external perturbation significantly degrades balance and increases the risk of falls, so methods to improve postural control under such perturbation are expected to be beneficial. Considering the important role of somatosensory feedback from ankle tendons in balance regulation, we proposed that applying adhesive elastic tapes to the ankle tendons may affect the postural control. In this initial pilot study, we recruited four healthy young adults and instructed them to balance under forward and backward perturbation which was applied at unpredictable timing by an electrically controlled actuator. The task was performed with and without the application of tapes. We found that cutaneous stimulation to the ankle tendons significantly reduced the peak displacement of the center of pressure (p = 0.008), and changed activations of multiple muscles (gastrocnemius medialis: p = 0.041, biceps femoris: p = 0.023, and erector spinae: p = 0.035) under forward direction perturbation. In contrast, no significant difference was observed under backward direction perturbation. Our findings suggest that cutaneous stimulation by applying adhesive elastic tapes can affect the postural control under unpredictable external perturbation, but its effect may depend on the direction of the perturbation

EFFECTS OF CALF ANCHORING COMPRESSION LEVELS ON ANKLE KINEMATICS, MOTOR UNIT BEHAVIOR, ENERGY COST, AND DISCOMFORT DURING WALKING

We propose a method for quantifying the anchoring compression of wearable devices using limb occlusion pressure (LOP). Under 0%, 20%, 40%, and 60% of LOP, five healthy male participants performed an isometric ankle plantarflexion task before and after walking on an inclined treadmill. Significant differences were shown in calf discomfort (p \u3c 0.001), and ankle plantarflexion angle (p = 0.013) during walking. Although no significant difference was found for oxygen consumption and motor unit behavior of the gastrocnemius medialis, the maintenance of ankle plantarflexion angle was related to an increase in peak motor unit action potential amplitude and average firing rate at 60% of LOP. The results suggest that subjective assessment is more sensitive than the physiological indices, and calf anchoring force should not exceed 60% LOP to avoid any possible negative effect on the muscle

The different contributions of the eight prefrontal cortex subregions to reactive responses after unpredictable slip perturbations and vibrotactile cueing

IntroductionRecent advancements in functional near-infrared spectroscopy technology have offered a portable, wireless, wearable solution to measure the activity of the prefrontal cortex (PFC) in the human neuroscience field. This study is the first to validate the different contributions made by the PFC's eight subregions in healthy young adults to the reactive recovery responses following treadmill-induced unpredictable slip perturbations and vibrotactile cueing (i.e., precues).MethodsOur fall-inducing technology platform equipped with a split-belt treadmill provided unpredictable slip perturbations to healthy young adults while walking at their self-selected walking speed. A portable, wireless, wearable, and multi-channel (48 channels) functional near-infrared spectroscopy system evaluated the activity of PFC's eight subregions [i.e., right and left dorsolateral prefrontal cortex (DLPFC), ventrolateral prefrontal cortex (VLPFC), frontopolar prefrontal cortex (FPFC), and orbitofrontal cortex (OFC)] as quantified by oxyhemoglobin and deoxyhemoglobin concentrations. A motion capture system and two force plates beneath the split-belt treadmill were used to quantify participants' kinematic and kinetic behavior. All participants completed 6 trials: 2 consecutive trials without vibrotactile cueing and with a slip perturbation (control trials); 3 trials with vibrotactile cueing [2 trials with the slip perturbation (cueing trial) and 1 trial without the slip perturbation (catch trial)], and 1 trial without vibrotactile cueing and with a slip perturbation (post-control trial). The PFC subregions' activity and kinematic behavior were assessed during the three periods (i.e., standing, walking, and recovery periods).ResultsCompared to the walkers' standing and walking periods, recovery periods showed significantly higher and lower levels of oxyhemoglobin and deoxyhemoglobin concentrations, respectively, in the right and left DLPFC, VLPFC, and FPFC, regardless of the presence of vibrotactile cueing. However, there was no significant difference in the right and left OFC between the three periods. Kinematic analyses confirmed that vibrotactile cueing significantly improved reactive recovery responses without requiring more involvement by the PFC subregions, which suggests that the sum of attentional resources is similar in cued and non-cued motor responses.DiscussionThe results could inform the design of wearable technologies that alert their users to the risks of falling and assist with the development of new gait perturbation paradigms that prompt reactive responses

ASSOCIATION BETWEEN AGE AND BODY’S KINEMATIC RESPONSES TO UNPREDICTABLE GAIT PERTURBATION

This study assessed the body’s kinematic responses to unpredictable gait perturbations repeatedly induced by a fall-inducing technology platform in young and older adults. Ten young adults (young group) and ten older adults (older group) completed two trials with the gait perturbation (i.e., trip). Maximum trunk flexion angle, maximum right hip flexion angle, and minimum whole-body center of mass (COM) position quantified the body’s kinematic responses for a pre-trip period and a recovery period. The results showed that both groups significantly increased maximum trunk flexion angle and maximum right hip flexion angle during the recovery period compared to the pre-trip period. The young group showed a significantly decreased minimum COM position during the recovery period compared to the pre-trip period. Our findings can inform perturbation-based gait training in young and older adults to improve the body’s responses for fall reduction and prevention

On the dynamics of a quadruped robot model with impedance control: Self-stabilizing high speed trot-running and period-doubling bifurcations

The MIT Cheetah demonstrated a stable 6 m/s trot gait in the sagittal plane utilizing the self-stable characteristics of locomotion. This paper presents a numerical analysis of the behavior of a quadruped robot model with the proposed controller. We first demonstrate the existence of periodic trot gaits at various speeds and examine local orbital stability of each trajectory using Poincar`e map analysis. Beyond the local stability, we additionally demonstrate the stability of the model against large initial perturbations. Stability of trot gaits at a wide range of speed enables gradual acceleration demonstrated in this paper and a real machine. This simulation study also suggests the upper limit of the command speed that ensures stable steady-state running. As we increase the command speed, we observe series of period-doubling bifurcations, which suggests presence of chaotic dynamics beyond a certain level of command speed. Extension of this simulation analysis will provide useful guidelines for searching control parameters to further improve the system performance.United States. Defense Advanced Research Projects Agency. Maximum Mobility and Manipulation (M3) Progra