Background: In their current laboratory-based form, existing vibrotactile sensory augmentation technologies that provide cues of body motion are impractical for home-based rehabilitation use due to their size, weight, complexity, calibration procedures, cost, and fragility.Methods: We have designed and developed a cell phone based vibrotactile feedback system for potential use in balance rehabilitation training in clinical and home environments. It comprises an iPhone with an embedded tri-axial linear accelerometer, custom software to estimate body tilt, a "tactor bud" accessory that plugs into the headphone jack to provide vibrotactile cues of body tilt, and a battery. Five young healthy subjects (24 ± 2.8 yrs, 3 females and 2 males) and four subjects with vestibular deficits (42.25 ± 13.5 yrs, 2 females and 2 males) participated in a proof-of-concept study to evaluate the effectiveness of the system. Healthy subjects used the system with eyes closed during Romberg, semi-tandem Romberg, and tandem Romberg stances. Subjects with vestibular deficits used the system with both eyes-open and eyes-closed conditions during semi-tandem Romberg stance. Vibrotactile feedback was provided when the subject exceeded either an anterior-posterior (A/P) or a medial-lateral (M/L) body tilt threshold. Subjects were instructed to move away from the vibration.Results: The system was capable of providing real-time vibrotactile cues that informed corrective postural responses. When feedback was available, both healthy subjects and those with vestibular deficits significantly reduced their A/P or M/L RMS sway (depending on the direction of feedback), had significantly smaller elliptical area fits to their sway trajectory, spent a significantly greater mean percentage time within the no feedback zone, and showed a significantly greater A/P or M/L mean power frequency.Conclusion: The results suggest that the real-time feedback provided by this system can be used to reduce body sway. Its advantages over more complex laboratory-based and commercial balance training systems in terms of cost, size, weight, functionality, flexibility, and accessibility make it a good candidate for further home-based balance training evaluation.

We have developed a mobile instrument for motion instruction and correction (MIMIC) that enables an expert (i.e., physical therapist) to map his/her movements to a trainee (i.e., patient) in a hands-free fashion. MIMIC comprises an expert module (EM) and a trainee module (TM). Both the EM and TM are composed of six-degree-of-freedom inertial measurement units, microcontrollers, and batteries. The TM also has an array of actuators that provide the user with vibrotactile instructional cues. The expert wears the EM, and his/her relevant body position is computed by an algorithm based on an extended Kalman filter that provides asymptotic state estimation. The captured expert body motion information is transmitted wirelessly to the trainee, and based on the computed difference between the expert and trainee motion, directional instructions are displayed via vibrotactile stimulation to the skin. The trainee is instructed to move in the direction of the vibration sensation until the vibration is eliminated. Two proof-of-concept studies involving young, healthy subjects were conducted using a simplified version of the MIMIC system (pre-specified target trajectories representing ideal expert movements and only two actuators) during anterior-posterior trunk movements. The first study was designed to investigate the effects of changing the expert-trainee error thresholds (0.5°, 1.0°, and 1.5°) and varying the nature of the control signal (proportional, proportional plus derivative). Expert-subject cross-correlation values were maximized (0.99) and average position errors (0.33°) and time delays (0.2 s) were minimized when the controller used a 0.5° error threshold and proportional plus derivative feedback control signal. The second study used the best performing activation threshold and control signal determined from the first study to investigate subject performance when the motion task complexity and speed were varied. Subject performance decreased as motion speed and complexity increased.

This study investigates the influence of two types of gait perturbation (i.e., trip and slip) induced by a programmable split-belt treadmill on the body’s compensatory responses. Our fall-inducing technology equipped with a commercially available programmable split-belt treadmill provides unpredictable trip and slip perturbations during walking. Two force plates beneath the split-belt treadmill and a motion capture system quantify the body’s kinetic and kinematic behaviors, and a wireless surface electromyography (EMG) system evaluates the lower limb muscle activity. Twenty healthy young adults participated. The perturbations (i.e., trip and slip) were applied randomly to the participant’s left foot between the 31st and 40th steps. The kinetic and kinematic behaviors and lower limb muscle activity were assessed during the standing, walking, and recovery periods. Compared to trip perturbations, stepping responses to slip perturbations were quicker and trunk, shoulder, and whole body center of mass movements after slip perturbations were higher; EMG results showed that tibialis anterior, gastrocnemius, rectus femoris, and biceps femoris activities were also higher. The two common types of gait perturbation (i.e., trip and slip) induced by a commercially available programmable split-belt treadmill influenced the body’s compensatory responses.

Trips and slips, the two most common gait perturbations, often cause falls. Multiple studies have focused mainly on the kinematics of multiple body segments in response to an unexpected trip or slip induced by mechanical obstacles, cables, treadmills, and slippery agents or contaminants on a floor. Few studies have examined the joint moments of the compensatory limb following an unexpected trip on an obstacle. This proof-of-concept study sought to assess the ankle, knee, and hip moments of the compensatory limb during normal walking and the first stepping response following the two most common gait perturbations. Eighteen healthy young adults completed 4 trials (2 trials with a random trip perturbation and 2 trials with a random slip perturbation) while walking on a split-belt treadmill. In each trial, the motorized treadmill induced either an unexpected trip or slip perturbation to the left foot between the 31 st and 40th step randomly. A motion capture system recorded the positions of body segments, the joint moments (i.e., ankle, knee, and hip moments) of the compensatory limb were quantified, and the maximum joint moments were assessed during normal walking and the first stepping response. Compensatory limb's ankle plantarflexion, knee flexion, hip flexion, and hip extension moments were significantly higher for a slip perturbation than for a trip perturbation during the first stepping response. Compensatory limb's knee flexion, hip flexion, and hip extension moments were also significantly higher during the first stepping response to a slip perturbation compared to normal walking. This proof-of-concept study is the first to investigate the ankle, knee, and hip moments of the compensatory limb during the first stepping response following unexpected gait perturbations induced by a split-belt treadmill. The findings are expected to improve the gait perturbation paradigms developed for training balance-impaired individuals.

Many stroke survivors have limited ankle range of motion (ROM) caused by weak dorsiflexors and stiff plantarflexors. Passive ankle stretching exercises with physical therapists or a stretching board are usually recommended, but these treatments have some limitations (e.g., cost, availability of physical therapists, etc.). In this paper, we assessed the results of ankle stretching exercises delivered by a robotic ankle stretching system called Motorized Ankle Stretcher (MAS) that we developed or by a stretching board on ankle ROM, balance control, and gait performance. Sixteen stroke survivors were randomly assigned to an intervention group (IG) or a control group (CG), and participated in seven sessions of dorsiflexion stretching exercises for three-and-a-half consecutive weeks. Laboratory assessments included pre-assessment (baseline at the beginning of the first exercise session), post-assessment (at the end of the seventh exercise session), and retention-assessment (one month after the seventh exercise session). All assessments included ankle ROM for the affected side, static/dynamic balance control with a Sensory Organization Test (SOT), walking speed, walking cadence, and step length for the affected and unaffected sides. During seven sessions of ankle stretching exercises, the IG performed them using the MAS, and the CG used a stretching board. The IG significantly improved ankle ROM, SOT scores (i.e., static/dynamic balance control), walking speeds, walking cadences, and step lengths for the unaffected side after completing the seven exercise sessions of ankle stretching exercises, and maintained the enhancements at the retention-assessment. The CG did not significantly improve across the majority of outcome measures except for the SOT scores between the pre- and retention-assessments. Future work will investigate the ideal intensity, frequency, and duration of exercising with the MAS. Our research on technology-assisted ankle rehabilitation, which can ascertain the level of persistent improvement, long-term performance retention, and carry-over effects in stroke survivors, can be used to inform future designs.

Telerehabilitation technology often helps individuals with Parkinson’s disease (PD) to control their balance and improve postural stability. This proof-of-concept study describes the redesign of a smartphone-based wearable balance rehabilitation system, or Smarter Balance System (SBS) intended for in-home use, and determines the number of exercise sessions required to achieve steady-state balance exercise performance by people with PD who performed 6 weeks of in-home dynamic weight-shifting balance exercises. The redesigned SBS supplied real-time multimodal (visual and vibrotactile) biofeedback during dynamic weight-shifting balance exercises (WSBEs). A Technology Acceptance Model (TAM) questionnaire completed by participants validated its acceptability and use. The results of regression analyses of participants’ balance exercise performance, based on the average cross-correlations and absolute position errors between the target motion and the exerciser’s motion, showed exponential trends, a performance plateau after 3 weeks, and a quasi-steady state performance by the end of 6 consecutive weeks.