The effect of force-controlled biting on human posture control

Several studies have confirmed the neuromuscular effects of jaw motor activity on the postural stability of humans, but the mechanisms of functional coupling of the craniomandibular system (CMS) with human posture are not yet fully understood. The purpose of our study was, therefore, to investigate whether submaximum biting affects the kinematics of the ankle, knee, and hip joints and the electromyographic (EMG) activity of the leg muscles during bipedal narrow stance and single-leg stance. Twelve healthy young subjects performed force-controlled biting (FB) and non-biting (NB) during bipedal narrow stance and single-leg stance. To investigate the effects of FB on the angles of the hip, knee, and ankle joints, a 3D motion-capture system (Vicon MX) was used. EMG activity was recorded to enable analysis of the coefficient of variation of the muscle co-contraction ratios (CVR) of six pairs of postural muscles. Between FB and NB, no significant differences were found for the mean values of the angles of the ankle, knee, and hip joints, but the standard deviations were significantly reduced during FB. The values of the ranges of motion and the mean angular velocities for the three joints studied revealed significant reduction during FB also. CVR was also significantly reduced during FB for five of the six muscle pairs studied. Although submaximum biting does not change the basic strategy of posture control, it affects neuromuscular co-contraction patterns, resulting in increased kinematic precision.     

A unified approach for revealing multiple balance recovery strategies

In human balance recovery, different strategies have been proposed with generally overlooked knee motions but extensive focus on the ankle, hip, and step strategies. It is not well understood whether maintaining balance is regulated at the lower “muscular–articular” level of coordinating segment joints or at a higher level of controlling whole body dynamics. Whether balance control is to minimize joint degrees of freedom (DOF) or utilize all the available DOF also remains unclear. This study aimed to use a realistic musculoskeletal human model to identify multiple balance recovery strategies with a single optimization criterion. Movements were driven by neural excitations (which activated muscle force generation) and were assumed to be symmetric. Balance recoveries were simulated with forward-inclined straight body postures as the initial conditions. When the position of the toes was fixed, balance was regained with virtually straight knees and mixed ankle/hip strategies. Under a severely perturbed condition, use of the forward hop strategy after releasing the fixed-toes constraint indicated spontaneous recruitment or suppression of DOF, which mimicked functions of optimally computed CNS commands in humans. The results also indicated that increase/decrease in the number of DOF depends on the imposed perturbation intensity and movement constraints.     

Muscle force compensation among synergistic muscles after fatigue of a single muscle

PurposeThe aim of this study was to examine control strategies among synergistic muscles after fatigue of a single muscle. It was hypothesized that the compensating mechanism is specific for each fatigued muscle.MethodsThe soleus (SOL), gastrocnemius lateralis (GL) and medialis (GM) were fatigued in separate sessions on different days. In each experiment, subjects (n = 11) performed maximal voluntary contractions prior to and after fatiguing a single muscle (SOL, GL or GM) while the voluntary muscle activity and torque were measured. Additionally, the maximal single twitch torque of the plantarflexors and the maximal spinal reflex activity (H-reflex) of the SOL, GL and GM were determined. Fatigue was evoked using neuromuscular stimulation.ResultsFollowing fatigue the single twitch torque decreased by −20.1%, −19.5%, and −23.0% when the SOL, GL, or GM, have been fatigued. The maximal voluntary torque did not decrease in any session but the synergistic voluntary muscle activity increased significantly. Moreover, we found no alterations in spinal reflex activity.ConclusionsIt is concluded that synergistic muscles compensate each other. Furthermore, it seems that self-compensating mechanism of the fatigued muscles occurred additionally. The force compensation does not depend on the function of the fatigued muscle.     

The role of trait emotional intelligence in academic performance during the university transition: An integrative model of mediation via social support,coping, and adjustment

The authors propose conceptual models linking trait emotional intelligence (TEI) with achievement both directly and indirectly via perceived social support (PSS), engagement coping (EC), and adjustment, in the context of the university transition. The models were tested in a multiwave design with a sample of incoming Australian undergraduates (N = 470). In structural equation analyses, TEI was found to be a direct predictor of higher PSS and the greater use of EC strategies. Further, mediation analyses revealed that TEI was indirectly associated with academic adjustment via EC and psychological adjustment via EC and PSS operating in parallel. TEI was also found to be indirectly associated with achievement via EC and academic adjustment linked serially in a three-path mediated sequence. These direct and indirect relations were robust when controlling for known confounding influences. The empirically supported mediating processes extend the literature by elucidating some of the pathways through which TEI is linked with better adjustment and achievement.     

The mediating role of optimism in the relations between sense of coherence,subjective and psychological well-being among late adolescents

The purpose of this study was to examine whether optimism is a mediator between sense of coherence, subjective well-being and psychological well-being among late adolescents. Two hundred and eleven participants completed the Sense of Coherence Scale, the Life Orientation Test-Revised, the Satisfaction With Life Scale, the Positive and Negative Affect Schedule, and the Psychological Well-Being Scale. Results of path analysis revealed both direct and indirect effects of sense of coherence on subjective and psychological well-being measures, suggesting that optimism served as a partial mediator. The mediating role of optimism may be more fully understood within the framework of the self-concordance model. Consistent with the model, individuals who have formed meaningful goals tend to experience more positive affective states, which in turn enhances well-being. The findings also suggest that sense of coherence should not be interpreted as an autonomous resource contributing to a favorable development of late adolescents’ well-being, but as a factor that works in connection with dispositional optimism.     

Exposure,Agency, Perceived Threat,and Guilt as Predictors of Posttraumatic Stress Disorder in Veterans

Using a sample of 289 Iraq/Afghanistan veterans, this study examined the contributions of combat exposure, agency, perceived threat, and guilt to posttraumatic stress disorder (PTSD) symptoms. Regression analyses indicated the four variables (together with demographic variables) accounted for 79% of the variance in PTSD symptoms. Guilt was the most important predictor. In addition, guilt mediated between exposure and PTSD symptoms, perceived threat and PTSD symptoms, and agency and PTSD symptoms. Implications of these findings are discussed.     

Soldiers Lead Themselves to More Success: A Self-Leadership Intervention Study

Neck and Manz (1999) Neck, C. P., & Manz, C. C. (1999). In search of the self-led soldier: Army leadership in the twenty-first century. In J. G. Hunt, G. E. Dodge, & L. Wong (Eds.), Out of the box leadership: Transforming the twenty-first army and other top organizations (pp. 153–176). Stamford, CT: JAI Press. [Google Scholar] elaborated in their article “In Search of the Self-Lead Soldier” on the need for continuous improvement of personnel qualities such as increase in self-efficacy, increase of performance, and decrease of perceived strain. Self-leadership is a tool that fosters exactly these personal resources. This study examines self-leadership training effects on soldiers participating in a military training course over 14 weeks. It is the first self-leadership training study to evaluate performance improvement using objective criteria (examination marks, physical tests) in intervention and control group consisting of soldiers of the Austrian army. Its design features a large sample (N = 130), duration of self-leadership training over 10 weeks, and evaluation over 4 time points. The intervention group accomplished significantly higher educational achievements in examinations and physical tests. Also levels of self-efficacy were significantly higher and levels of strain were marginally to significantly lower.     

Development of Indirect Measures of Conscientiousness: Combining a Facets Approach and Network Analysis

Because indirect measures of personality self‐concepts such as the Implicit Association Test (IAT) allow tapping into automatic processes, they can offer advantages over self‐report measures. However, prior investigations have led to mixed results regarding the validity of indirect measures of conscientiousness. We suggest that these results might be due to a failure to consider the different facets of conscientiousness. These facets are of crucial importance because they are associated differentially with other psychobiological constructs and they are also characterized by different mechanisms. Therefore, focusing on facets while developing indirect measures of conscientiousness may improve the validity of such measures. In Study 1, we conducted a psycholexical investigation to develop one IAT for each conscientiousness facet. In Study 2, we examined the convergent and discriminant validities of each facet IAT in relation to self‐report measures, peer‐report measures and self‐report behavioural indicators, and we investigated differential associations of the conscientiousness facets with working memory capacity and self‐control. We employed network analysis as a novel approach to elucidate differential relationships involving personality facets. The results corroborated the convergent and discriminant validity of the conscientiousness facet IATs with self‐reports and showed that the conscientiousness facets were differentially associated with working memory capacity and with self‐control. Copyright © 2015 European Association of Personality Psychology