Differences in activation patterns between eccentric and concentric quadriceps contractions.

Previous studies analysing electromyograms (EMGs) from indwelling electrodes have indicated that fast-twitch motor units are selectively recruited for low-intensity eccentric contractions. The aim of this study was to compare the frequency content of surface EMGs from quadriceps muscles during eccentric and concentric contractions at various contraction intensities. Electromyograms were recorded from the rectus femoris, vastus lateralis and vastus medialis muscles of 10 men during isokinetic (1.05 rad x s(-1)) eccentric and concentric knee extension contractions at 25%, 50%, 75% and 100% of maximal voluntary contraction (MVC) for each contraction mode. Additionally, isometric contractions (70 degrees) were performed at each intensity. The mean frequency and root mean square (RMS) of the surface EMG were computed. Mean frequency was higher for eccentric than concentric contractions at 25% (P < 0.01), 50% (P < 0.01) and 75% (P < 0.05) but not at 100% MVC. It increased with increasing contraction intensity for isometric (P < 0.001) and concentric (P < 0.01) contractions but not for eccentric contractions (P = 0.27). The EMG amplitude (RMS) increased with increasing contraction intensity similarly in each contraction mode (P < 0.0001). Higher mean frequencies for eccentric than concentric contractions at submaximal contraction intensities is consistent with more fast-twitch motor units being active during eccentric contractions.     

Adjunct question effects with review

The effects on retention of adjunct questions either placed at the end of a passage or inserted after their respective paragraphs within the passage were examined. The high school subjects were encouraged to review the materials after encountering the questions, a departure from traditional procedures in the field. Both treatments led to superior retention of the previously questioned facts when compared to a passage-only control group, but did not increase retention of previously unquestioned facts. The position of the adjunct questions did not differentially affect performance. The discrepancy of the results from those traditionally reported are interpreted in terms of the procedures employed.     

Measuring Socioeconomic Status at the School Level

Why is there an increased need for quantitative indicators of student socioeconomic status at the school level? What alternative approaches have been used to measure SES? Can principals accurately estimate the SES distribution of their student populations? How do their estimates correlate with other indexes o f family SES?     

缩微胶片复制技术

<正> 缩微摄影积极而活跃地闯进了人们的生活。因此,图书馆的广大读者们,越来越需要利用的不是图书和杂志,而是它们的缩微复制品和显微阅读设备。而图书馆的工作人员们,则越来越需要配套的、复杂的缩微摄影复制设备的网络体系。普及缩微胶片复制技术的理由是十分明显而又充分的。因为这种复制技术,能够解决图书馆界很久以前就已面临的、特别是当今又正在日益加剧的许多问题。和传统的大开本印刷品相比较,缩微胶片复制品可以     

The marketing audit: a new perspective on library services and products

A marketing audit enables a library to look at audiences, services, and products with a structured approach. The audit can be used to assess operations and to provide a framework for ongoing decision making, evaluation, and long-range planning. An approach to the audit process is presented and its application is demonstrated in a case study featuring the American Hospital Association Resource Center.