Evaluating the feasibility of two post-hoc correction techniques for mitigating posture-induced measurement errors associated with wearable motion capture.

Wearable motion capture systems are commonly used to measure body kinematics outside of laboratory settings. However, commercially available systems are designed to be used with typically developed adult populations, and assume users begin with a typical standing posture. Individuals with cerebral palsy and other neuromuscular pathologies often present atypical postures that can introduce significant errors in kinematics measurements from wearable motion capture. This study examines two post-hoc correction techniques for rectifying posture-induced errors in kinematic data: (1) Direct three-dimensional realignment of the measured body segment orientations, or (2) adding the initial static joint angle to the dynamic joint angle measurements. Gait kinematics were measured for eight able-bodied participants using a commercial wearable motion capture system. Participants walked with a typical gait, simulated crouch gait, and simulated equinus. The resulting kinematics from the uncorrected and post-hoc corrected trials were compared against simultaneously recorded measurements from an optoelectric motion capture system. Both correction techniques significantly decreased the posture-induced errors in lower-limb joint angle measurements. This work establishes a basis for the application of post-hoc correction techniques, aimed at improving the performance of wearable kinematic measurement systems when used with individuals having non-typical postures.

Evaluating and improving the performance of thin film force sensors within body and device interfaces.

Thin film force sensors are commonly used within biomechanical systems, and at the interface of the human body and medical and non-medical devices. However, limited information is available about their performance in such applications. The aims of this study were to evaluate and determine ways to improve the performance of thin film (FlexiForce) sensors at the body/device interface. Using a custom apparatus designed to load the sensors under simulated body/device conditions, two aspects were explored relating to sensor calibration and application. The findings revealed accuracy errors of 23.3±17.6% for force measurements at the body/device interface with conventional techniques of sensor calibration and application. Applying a thin rigid disc between the sensor and human body and calibrating the sensor using compliant surfaces was found to substantially reduce measurement errors to 2.9±2.0%. The use of alternative calibration and application procedures is recommended to gain acceptable measurement performance from thin film force sensors in body/device applications.

A Method for Evaluating Timeliness and Accuracy of Volitional Motor Responses to Vibrotactile Stimuli.

Artificial sensory feedback (ASF) systems can be used to compensate for lost proprioception in individuals with lower-limb impairments. Effective design of these ASF systems requires an in-depth understanding of how the parameters of specific feedback mechanism affect user perception and reaction to stimuli. This article presents a method for applying vibrotactile stimuli to human participants and measuring their response. Rotating mass vibratory motors are placed at pre-defined locations on the participant's thigh, and controlled through custom hardware and software. The speed and accuracy of participants' volitional responses to vibrotactile stimuli are measured for researcher-specified combinations of motor placement and vibration frequency. While the protocol described here uses push-buttons to collect a simple binary response to the vibrotactile stimuli, the technique can be extended to other response mechanisms using inertial measurement units or pressure sensors to measure joint angle and weight bearing ratios, respectively. Similarly, the application of vibrotactile stimuli can be explored for body segments other than the thigh.

The Effects of Acute Intense Physical Exercise on Postural Stability in Children With Cerebral Palsy.

This study evaluated the effects of intense physical exercise on postural stability of children with cerebral palsy (CP). Center of pressure (CoP) was measured in 9 typically developing (TD) children and 8 with CP before and after a maximal aerobic shuttle-run test (SRT) using a single force plate. Anteroposterior and mediolateral sway velocities, sway area, and sway regularity were calculated from the CoP data and compared between pre- and postexercise levels and between groups. Children with CP demonstrated significantly higher pre-SRT CoP velocities than TD children in the sagittal (18.6 ± 7.6 vs. 6.75 1.78 m/s) and frontal planes (15.4 ± 5.3 vs. 8.04 ± 1.51 m/s). Post-SRT, CoP velocities significantly increased for children with CP in the sagittal plane (27.0 ± 1.2 m/s), with near-significant increases in the frontal plane (25.0 ± 1.5m/s). Similarly, children with CP evidenced larger sway areas than the TD children both pre- and postexercise. The diminished postural stability in children with CP after short but intense physical exercise may have important implications including increased risk of falls and injury.

Effects of cognitive load and prosthetic liner on volitional response times to vibrotactile feedback.

Artificial tactile feedback systems can improve prosthetic function for people with amputation by substituting for lost proprioception in the missing limb. However, limited data exists to guide the design and application of these systems for mobility and balance scenarios. The purpose of this study was to evaluate the performance of a noninvasive artificial sensory feedback (ASF) system on lower-limb function in the presence of a cognitive load and a liner interface. Reaction times (RTs) and accuracy of leg-movement responses to vibratory stimuli at the thigh were recorded for 12 nondisabled individuals and 3 participants with transfemoral amputation using a custom-built testing apparatus. The results indicate that the addition of a cognitive load increases response times relative to the baseline condition by 0.26 to 0.33 s. The prosthetic liner produced a less pronounced increase in RT of 0.06 to 0.11 s. Participants were able to correctly identify the stimulus location with nearly 100% accuracy. These increased RTs are nontrivial and must be considered in designing ASF systems.

Analysis of terrain effects on the interfacial force distribution at the hand and forearm during crutch gait.

Forces transferred to the upper body during crutch use can lead to both short-term and long-term injuries, including joint pain, crutch palsy, and over-use injuries. While this force transmission has been studied in controlled laboratory settings, it is unclear how these forces are affected by irregular terrains commonly encountered during community ambulation. The purpose of this study was to determine the effects of walking speed and uneven terrain on the load magnitude, distribution, and rate of loading at the human-crutch contact surfaces. Our results show that the rates of loading were significantly increased with higher walking speeds and while negotiating certain irregular terrains, despite there being no apparent effect on the peak force transmission, suggesting load rate may be a more appropriate metric for assessing terrain effects on crutch gait. Furthermore, irrespective of the type of terrain and walking condition, the largest compressive forces were found to reside in the carpal-tunnel region of the hand, and may therefore be a primary contributor to carpal-tunnel injury.

The effect of platelet-rich plasma on muscle contusion healing in a rat model.

BACKGROUND: Current therapy for muscle contusions is usually limited to nonsteroidal anti-inflammatory drugs and/or use of the RICE principle (rest, ice, compression, elevation); thus, other forms of treatment that can potentially accelerate the rate of healing are desirable. HYPOTHESES: A local injection of platelet-rich plasma (PRP) would lead to accelerated healing rates compared with controls; also, delayed administration of PRP would lead to a blunted response compared with immediate treatment. STUDY DESIGN: Controlled laboratory study. METHODS: Forty-six male Lewis rats each underwent a single blunt, nonpenetrating impact to the gastrocnemius muscle via a drop-mass technique and subsequently received either a single injection of saline into the area of injury immediately after injury (controls, n = 11) or rat PRP (either immediately after injury [PRP day 0, n = 12], the first day after injury [PRP day 1, n = 12], or the third day after injury [PRP day 3, n = 11]). The primary outcome was maximal isometric torque strength of the injured muscle, which was assessed before injury as well as on postinjury days 1, 4, 7, 10, and 14. All animals were sacrificed on postinjury day 15. Histological and immunohistochemical analyses were performed on 6 specimens from each group after sacrifice. RESULTS: The mean platelet concentration in the PRP was 2.19 × 10(6) (±2.69 × 10(5))/µL. The mean white blood cell count in the PRP was 22.54 × 10(3)/µL. Each group demonstrated statistically significant decreases in maximal isometric torque strength after injury when compared with preinjury levels, followed by significant increases back toward baseline values by postinjury day 14 (controls, 90.6% ± 7.90%; PRP day 0, 105.0% ± 7.60%; PRP day 1, 92.4% ± 7.60%; PRP day 3, 77.8% ± 7.90%) (P = .121). There were no statistically significant differences between the treatment and control groups at any of the time points. There were also no statistically significant differences between any of the groups in the percentage of centronucleated fibers (controls, 3.31% ± 5.10%; PRP day 0, 0.62% ± 1.59%; PRP day 1, 3.24% ± 5.77%; PRP day 3, 2.13% ± 3.26%) (P = .211) or the presence of inflammatory cells and macrophages. CONCLUSION: In this rat contusion model, a local injection of PRP into the injured gastrocnemius muscle resulted in no significant differences in functional or histological outcomes, indicating no likely benefit to healing. Additionally, there was no significant difference between immediate or delayed administration of PRP. CLINICAL RELEVANCE: Before PRP can be recommended for the treatment of muscle contusion injuries, further translational and clinical investigations need to be performed.