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

Two mechanisms have been suggested to explain stretching-induced maximum force depression: a mechanical alteration in the stretched muscle and an impairment of neural activation. Electrical stimulation allows standardization of the level of muscle activation without being limited by neural control. The aim of this study was to evaluate the stretching-induced changes in the electrical and mechanical properties of muscle during electrically elicited contractions. Twelve participants (age 22 +/- 1 years; body mass 75 +/- 2 kg; stature 1.79 +/- 0.02 m; mean +/- standard error) underwent six electrical stimulations of the medial gastrocnemius muscle before and after stretching. During the contractions, surface electromyogram (EMG) and mechanomyogram (MMG) were recorded simultaneously together with force. After stretching we found: (i) no differences in EMG parameters; (ii) MMG amplitude decreased by 4 +/- 1% (P < 0.05); and (iii) the peak force, the peak rate of force development, and the acceleration peak of force development decreased by 12 +/- 3%, 14 +/- 1%, and 24 +/- 5%, respectively (P < 0.05). In conclusion, acute passive stretching did not change EMG properties but altered the mechanical characteristics of the contracting muscle. Indeed, muscle force-generating capacity and stiffness of the muscle-tendon unit were significantly impaired.     

Connecting photosynthesis and cellular respiration: Preservice teachers' conceptions

The biological processes of photosynthesis and plant cellular respiration include multiple biochemical steps, occur simultaneously within plant cells, and share common molecular components. Yet, learners often compartmentalize functions and specialization of cell organelles relevant to these two processes, without considering the interconnections as well as the significance of the plant as an independent biological system functioning as a nested component within local and global ecosystems. Understanding connections among biological systems at macro and micro levels is important to biological literacy. This study examined preservice elementary teachers' conceptions of photosynthesis and plant cellular respiration, with attention to interconnections and systems. Participants were limited in their understanding of the processes impacting multiple ecological levels, and they held inadequate representations of interconnections between the processes. Participants' views were laden with sociological and egocentric components. They often compared plant functions with analogous human functions. Most participants viewed plants as dependent on humans while having societal use. Justifications for views included nominal knowledge of the processes; experiential authoritarian reasoning; and anthropomorphism. We discuss instructional implications in light of the findings. © 2009 Wiley Periodicals, Inc. J Res Sci Teach 46: 791–812, 2009     

Prenatal programming of sporting success: Associations of digit ratio (2D:4D), a putative marker for prenatal androgen action,with world rankings in female fencers

Abstract

Associations of the second-to-fourth digit ratio (2D:4D), a putative marker for prenatal androgen action, and of absolute finger length, a putative marker for pubertal–adolescent androgen action, with sport performance were examined in a multinational sample of 87 world-class women épée fencers. Lower (masculinized) digit ratios correlated, although not significantly so, with better current and highest past world rankings. These correlations were significant for right-hand 2D:4D with controls for the most salient factors for 2D:4D (ethnicity) and world rankings (years of international experience, height, and weight). Longer (masculinized) fingers correlated strongly with better current and highest past world rankings; these correlations became insignificant with the same controls. Replicating previous evidence for fencers, left-handedness was much more prevalent in this sample (21%) than in the female general population, and left-handers had somewhat, but not significantly so, lower 2D:4D as well as better world rankings than right-handers. These findings extend related evidence suggestive of prenatal programming of aptitude across a variety of sports, especially running and soccer. Some known extragenital effects of prenatal testosterone that contribute to the development of efficient cardiovascular systems, good visuospatial abilities, physical endurance and speed, and to the propensity for rough-and-tumble play, apparently promote sporting success in adult life.     

School Chemistry: An Historical and Philosophical Approach

Since at least the eighteenth century scientific knowledge (then natural philosophy) was produced in groups of experts and specialists and was transmitted in schools, where, future experts and specialists were trained. The design of teaching has always been a complex process particularly in recent years when educational aims (for example, teaching scientific competence to everyone, not just to experts and specialists) present significant challenges. These challenges are much more than a simple reorganisation of the scientific knowledge pre-determined by the existing teaching tradition for different educational level. In the context of chemical education, the new teaching approaches should bring about not only the transmission of chemical knowledge but also a genuine chemical activity so as to ensure that students can acquire chemical thinking. Chemistry teaching should be revised according to contemporary demands of schooling. In order to move forward towards new teaching proposals, we must identify the genuine questions that generate ‘chemical criteria’ and we should focus on them for teaching. We think that a good strategy is to look for those criteria in the philosophy and history of chemistry, from the perspective of didactics of science. This paper will examine the following questions: (1) How can school science be designed as a world-modelling activity by drawing on the philosophy of science. (2) How can ‘stories’ about the emergence of chemical entities be identified by looking at the history of chemistry? (3) How can modelling strategies be structured in school chemistry activities?     

La construcción individual del sistema de numeración convencional

Resumen

El sistema de numeración posicional de base 10 constituye un objeto cultural, resultado de un largo y dificultoso desarrollo histórico, que se convierte en un objeto de conocimiento a asimilar por el niño. En este artículo se estudia el proceso de reconstrucción individual de este instrumento intelectual, a través de las producciones gráficas espontáneas de 100 niños de edades comprendidas entre los 6 y 10 años, obtenidas en situación de invención de sistemas de notación de cantidades. Las producciones de los niños, cuyas estrategias recuerdan en muchos casos a las empleadas en los sistemas de numeración históricos, describen una génesis. Esta se extiende desde producciones que no contemplan la estabilidad de los grafismos ni la posibilidad de combinarlos, hasta las que recurren al principio del valor posicional, pasando por producciones de tipo aditivo y producciones que intentan, sin conseguirlo, la transposición del sistema de numeración convencional.     

Prevalence of illicit drug use among the Italian athlete population with special attention on drugs of abuse: a 10-year review

The objective of this study was to assess the prevalence of illicit drugs use among young adults, in particular elite athletes. This study considers the data obtained from anti-doping analyses performed on nearly 100,000 urine samples from 2000 to 2009 by the World Anti-Doping Agency accredited Italian Anti-Doping Laboratory. The percentage of adverse analytical findings varies on a yearly basis, but it is in the range 1.0-1.8% (not considering atypical findings, such as an altered endogenous steroid profile). Among positive results, there is a high prevalence of stimulants and drugs of abuse. The drug of abuse found most frequently is the tetrahydrocannabinol (cannabis) metabolite, accounting for 0.2-0.4% of the total samples analysed (18% of the positive results). The second most frequently encountered drug is cocaine, as detected from cocaine metabolites, accounting for 0.1% of the total samples analysed (7% of positive results). Other stimulants found included amphetamines, ephedrines, carphedon, modafinil, and anorexic compounds. No amphetamine-like designer drugs were detected. These data are indicative of the widespread prevalence of cocaine and cannabis use among the young adult population. However, due to the particular population studied, it must be considered an underestimation of the phenomenon among elite athletes with respect to the general population.