The Model-Size Effect on Traditional and Modified Tests of Covariance Structures

The integration of modern methods for causal inference with latent class analysis (LCA) allows social, behavioral, and health researchers to address important questions about the determinants of latent class membership. In this article, 2 propensity score techniques, matching and inverse propensity weighting, are demonstrated for conducting causal inference in LCA. The different causal questions that can be addressed with these techniques are carefully delineated. An empirical analysis based on data from the National Longitudinal Survey of Youth 1979 is presented, where college enrollment is examined as the exposure (i.e., treatment) variable and its causal effect on adult substance use latent class membership is estimated. A step-by-step procedure for conducting causal inference in LCA, including multiple imputation of missing data on the confounders, exposure variable, and multivariate outcome, is included. Sample syntax for carrying out the analysis using SAS and R is given in an appendix.     

Muscle properties and coordination during voluntary movement

The aims of this review were to provide some insight into the theoretical problems and questions associated with muscle coordination and control of movement, to consider some of the experimental findings on force-sharing among synergistic muscles, and to discuss some of the practical implications of force-sharing and movement control for optimal performance in sports. Theoretically, the distribution problem is introduced and the problems and difficulties of this approach in making quantitative predictions of force-sharing among muscles is discussed. Experimentally, the force-sharing research in the cat ankle extensor muscles is critically evaluated, and a complete force-sharing picture is given for the soleus and (medial) gastrocnemius for tasks covering a large range of speeds and intensities. In the application section, optimal performance criteria in jumping and cycling are considered. Furthermore, the plasticity of skeletal muscle properties is illustrated using examples from high-performance sports. The review ends with a summary of the topics discussed and suggestions for future research.     

What Happened on July 21st: An Investigation of Trauma and Trigger Warnings in the English Classroom

The controversy surrounding trigger warnings has highlighted a mystifying confound in post-secondary education. Faculty, students and school bureaucracies are divided. While trigger warning proponents emphasise the value of protecting students with trauma histories from unscaffolded exposure to content related to sexuality, violence, race and political strife, agonists interpret the trigger warning as a threat to academic freedom, artistry and professor autonomy. This paper presents an episode that occurred at a prominent school of education, in which an instructor’s choice of content triggered a post-traumatic response in a student. As the story unfolds, the narrative shifts back and forth between the instructor’s and the student’s experience of the event. The piece concludes with a commentary made by a clinical psychologist and trauma expert, who weighs in on the challenges confronting both professors and students, as each attempts to navigate handling emotionally charged, potentially triggering contents in the post-secondary classroom.     

Electrical and mechanical response of skeletal muscle to electrical stimulation after acute passive stretching in humans: A combined electromyographic and mechanomyographic approach

Abstract

Flexural and torsional rigidity are important properties of skis. However, the flexural and torsional rigidity that lead to optimal performance remain to be established. In the present study, four pairs of slalom skis that differed in flexural and torsional rigidity were tested by advanced and expert skiers. Using a 10-item questionnaire, different aspects of the skis' performance were rated on a 9-point scale. For each pair of skis, physical measurements were compared with the ratings of the two groups of skiers. Correlations (Spearman) were then determined between (i) different mechanical properties of the skis (static and dynamic), (ii) subjective assessments of the participants, and (iii) properties of the skis and the participants' assessments. The latter showed that expert skiers rate the aspects of the skis more accurately than advanced skiers. Most importantly, expert skiers are particularly sensitive to torsion of the skis. These results suggest that such highly rated elements should be addressed in future ski designs.     

German fußball—recent developments and origins

Fußball is the most popular sport in Germany. The reasons for this extraordinary status and success of association football in Germany are complex. In this article, answers are searched for in the context of the historical development of German society. After a review of the recent development of German football and football historiography, the paper focuses on two issues relating to the origins of German football. These are the transformation of football in the then dominant body culture of gymnastics, and secondly its impact on the German process of nation-building. Both processes are not only linked, but also related to the concept of manliness in German sport and society. This is the reason why women’s football in Germany was not accepted until the late 1960s in German society—and British as well.     

Effects of sample duration and spaced repetition upon delayed matching-to-sample in monkeys (Macaca arctoides andSaimiri sciureus)

Delayed matching-to-sample was used to study the effects of sample presentation time and spaced repetition upon delayed matching accuracy in one stumptail monkey and three squirrel monkeys. It was found in Experiment 1 that presenting the sample stimulus for 0.5 sec led to lower matching accuracy than was the case with longer presentation times of 2.5, 5.0, and 10.0 sec. Experiments 2 and 3 investigated the effects of temporally spacing the presentations of the sample stimulus. It was found that spaced repetition led to a deterioration of performance relative to massed repetition. These results are similar to the findings of experiments with pigeons and are contradictory to several previous experiments with monkeys or apes which found no effect of presentation time and a facilitative effect of spaced repetition. It is suggested that the use of monkeys inexperienced in short sample duration matching and tested in operant chambers using a limited set of noncomplex stimuli may be responsible for the discrepancies between these results and those of other experiments with primates.     

Analysis of elbow muscle strength parameters in Brazilian jiu-jitsu practitioners

Upper-body dynamic and isometric maximum strength are essential components for success in Brazilian jiu-jitsu (BJJ). This study was aimed at analysing strength parameters in the elbow flexor and extensor muscles of BJJ practitioners. Participants (n = 28) performed maximum isometric contractions of elbow flexors and extensors to determine peak torque (PT), rate of force development (RFD), and the torque–angle (T–A) relationship at elbow angles of 45°, 60°, 75°, 90°, 105°, and 120°. Additionally, concentric and eccentric PTs were measured at 1.04 rad·s^-1. Student t-test and ANOVA were performed using α = 0.05. Elbow flexors were stronger isometrically (P < 0.001, ES = 1.23) but weaker concentrically (P < 0.05, ES = 0.54) than extensor muscles, possibly because of the extensive grip disputes and pushing of opponents in BJJ. The T–A relationship had an inverted “U”-shape. Torque differences across elbow angles were moderate (ES = 0.62) for the extensor and large (ES = 0.92) for the flexor muscles. Isometric torque was greatest for elbow angles of 105° and 75° and smallest for 45° and 120° for extensor and flexor muscles, respectively. Elbow flexors had a greater RFD than extensors, regardless of elbow angle. The present study provides comprehensive results for elbow muscle strength in BJJ practitioners.