Alterations in stride-to-stride variability during walking in individuals with chronic ankle instability

The aim of this study was to evaluate stride-to-stride variability of the lower extremity during walking in individuals with and without chronic ankle instability (CAI) using a nonlinear analysis. Twenty-five participants with self-reported CAI and 27 healthy control participants volunteered for this study. Participants walked on a motor-driven treadmill for 3 min at their selected speed. Lower extremity kinematics in the sagittal and frontal planes were recorded using a passive retroreflective marker motion capture system. The temporal structure of walking variability was analyzed with sample entropy (SampEn). The CAI group produced lower SampEn values in frontal-plane ankle kinematics compared to the control group (P = .04). No significant group differences were observed for SampEn values of other kinematics (P > .05). Participants with CAI demonstrated less stride-to-stride variability of the frontal plane ankle kinematics compared to healthy controls. Decreased variability of walking patterns demonstrated by participants with CAI indicates that the presence of CAI may be associated with a less adaptable sensorimotor system to environmental changes. The altered sensorimotor function associated with CAI may be targets for clinical interventions, and it is critical to explore how interventions protocols affect sensorimotor system function.     

An examination of muscle force control in individuals with a functionally unstable ankle

Previous studies suggest that functional ankle instability (FAI) may be associated with deficits in the ability to sense muscle forces. We tested individuals with FAI to determine if they have reduced ability to control ankle muscle forces, which is a function of force sense. Our test was performed isometrically to minimize the involvement of joint position sense and kinesthesia. A FAI group and a control group were recruited to perform an ankle force control task using a platform-based ankle robot. They were asked to move a cursor to hit 24 targets as accurately and as fast as possible in a virtual maze. The cursor movement was based on the direction and magnitude of the forces applied to the robot. Participants underwent three conditions: pre-test (baseline), practice (skill acquisition), and post-test (post skill acquisition). The force control ability was quantified based on the accuracy performance during the task. The accuracy performance was negatively associated with the collision count of the cursor with the maze wall. The FAI group showed reduced ability to control ankle muscle forces compared to the control group in the pre-test condition, but the difference became non-significant in the post-test condition after practice. The change in performance before and after practice may be due to different degrees of reliance on force sense.     

Neuromuscular control in individuals with chronic ankle instability: A comparison of unexpected and expected ankle inversion perturbations during a single leg drop-landing

While neuromuscular control deficits during inversion perturbations in chronic ankle instability (CAI) cohorts are well documented in the literature, anticipatory motor control strategies to inversion perturbations in CAI are largely unknown. The purpose of this study was to examine neuromuscular control and ankle kinematics in individuals with CAI (n = 15) and matched controls (n = 15) during unexpected and expected single leg drop-landings onto a tilted surface rotated 20° in the frontal plane. Muscle activity from 200 ms pre- to post-landing was recorded from the tibialis anterior (TA), medial gastrocnemius (MG), peroneus longus (PL) and peroneus brevis (PB). Mean muscle activity, co-contraction index (CCI), and peroneal latency was analyzed. Ankle inversion angle at initial contact, time to maximum inversion angle, maximum inversion angle and velocity were also assessed. Significantly longer PL latency, less time to maximum inversion and greater maximum inversion angle was found in CAI compared to controls. Regarding landing condition, significantly greater maximum inversion angle, less inversion at initial contact, longer PB latency, less TA activity and frontal plane CCI during the post-landing phase was found during the unexpected perturbation. Prolonged PL latency and altered ankle kinematics suggests reduced frontal plane ankle stabilization in CAI. However, similar motor control strategies were utilized in both groups during the ankle inversion perturbations.     

Mediation analysis of decisional balance,sun avoidance and sunscreen use in the precontemplation and preparation stages for sun protection

Objective: Mediation analyses of sun protection were conducted testing structural equation models using longitudinal data with three waves. An effect was said to be mediated if the standardised path between processes of change, decisional balance and sun protection outcomes was significant.

Design: Longitudinal models of sun protection using data from individuals in the precontemplation (N = 964) and preparation (N = 463) stages who participated of an expert system intervention.

Main outcome measures: Nine processes of change for sun protection, decisional balance constructs of sun protection (pros and cons), sun avoidance behaviour and sunscreen use.

Results: With the exception of two processes in the preparation stage, processes of change predicted the pros (r = .126–.614), and the pros predicted the outcomes (r = .181–.272). Three models with the cons as mediator in the preparation stage, and none in the precontemplation stage, showed a mediated relationship between processes and outcomes.

Conclusion: In general, mediation analyses found both the process of change-to-pros and pros-to-behaviour paths significant for both precontemplation and preparation stages, and for both sun avoidance and sunscreen use outcomes. Findings provide support for the importance of assessing the role of underlying risk cognitions in improving sun protection adherence.     

Establishing motion control in children with autism and intellectual disability: Applications for anatomical and functional MRI

Excessive motion makes magnetic resonance imaging (MRI) extremely challenging among children with autism spectrum disorder (ASD). The medical risks of sedation establish the need for behavioral interventions to promote motion control among children with ASD undergoing MRI scans. We present a series of experiments aimed at establishing both tolerance of the MRI environment and a level of motion control that would be compatible with a successful MRI. During Study 1, we evaluated the effects of prompting and contingent reinforcement on compliance with a sequence of successive approximations to an MRI using a mock MRI. During Study 2, we used prompting and progressive differential reinforcement of other behaviors (DRO) to promote motion control in a mock MRI for increasing periods of time. Finally, during Study 3, some of the participants underwent a real MRI scan while a detailed in‐session motion analysis informed the quality of the images captured.     

Testing the health promotion model for adherence and quality of life in individuals with multiple sclerosis

The nature of multiple sclerosis (MS) presents challenges to health-promoting behaviors (e.g. adherence) and quality of life. The Health Promotion Model (HPM) proposes that these outcomes are explained by individual characteristics (i.e. biological, social, psychological) and behavior-specific cognitions (e.g. self-efficacy). The current study sought to test the HPM in explaining self-reported adherence and MS quality of life among 121 MS patients receiving care in an MS clinic in the southeastern United States. Hierarchical regression models partially supported the HPM for adherence (R² = .27) and more fully for quality of life (QoL) (R² = .64). Depression and stigma were among the variables most strongly related to both adherence and QoL; contrary to HPM theory, self-efficacy was not significantly related to adherence but was to QoL. Thus, the HPM may help to guide strategies used to improve QoL among individuals living with MS; however, the model may need further refinement to be used with adherence.