Comparing Numerical Methods to Estimate Vertical Jump Height Using a Force Platform

ABSTRACT

Males (n = 29) and females (n = 34) performed vertical jumps. Jump height was estimated from force platform data using five numerical methods and compared using intraclass correlation (ρ), and linear and rank regression standard error of estimate (SEE). Take-off velocity plus center of mass height at take-off and mechanical work methods were identical (ρ = 1.000) with small linear (SEE < 0.0001 cm) and rank order (SEE = 0) error. Integrating acceleration to displacement was nearly identical (ρ > 0.999), with small linear (SEE = 0.1 cm) and rank order (SEE < 1) errors compared to the above methods. Take-off velocity (ρ = 0.517) and flight time (ρ = 0.573) estimates were less than all other methods and had large linear (SEE ≥ 2.1 cm) and rank order (SEE > 4) errors. Take-off velocity and flight time methods should be avoided due to systematic and random error.     

西藏自治区首次发现灰雁Anser anser

灰雁是最常见的欧亚代表种,分为2个亚种,即指明亚种（西方亚种）A．a．anser和东方亚种A．a．rubrirostris。于2009年2月13日,在拉萨市达孜县境内的塔杰湿地记录到了灰雁东方亚种。塔杰湿地位于东经91°26’北纬29°44’,海拔3719m;被318国道分割为南北两个部分,北面的面积较大,仍具有天然湿地的生态学特性,南面的大部分已开垦为农田。本记录是西藏自治区境内的首次有关灰雁的报道,为西藏鸟类资源增添了一个新成员;更重要的是扩大了灰雁在我国乃至世界的分布范围。     

Forefoot and heel take-off strategies result in different distribution of lower extremity work during landings

ABSTRACT

Previous research suggests that landing mechanics may be affected by the mechanics of the preceding jump take-off. The purpose of the present study was to investigate whether jump take-off mechanics influence the subsequent landing mechanics. Female volleyball (n = 17) and ice hockey (n = 19) players performed maximal vertical jumps with forefoot and heel take-off strategies. During forefoot and heel jumps, participants were instructed to shift their weight to their forefoot or heel, respectively, and push through this portion of the foot throughout the jump. Jump mechanics were examined using 3D motion analysis, where lower extremity net joint moment (NJM) work, NJM, and segment angles were compared between forefoot and heel jumps using multivariate ANOVA. During jump take-off, participants performed more positive ankle plantar flexor and knee extensor NJM work in forefoot compared to heel jumps (P < 0.05). From initial foot contact to foot flat, participants performed more negative ankle plantar flexor and hip extensor NJM work during heel compared to forefoot jumps (P < 0.05). The present results demonstrate that using a heel take-off strategy results in a different distribution of lower extremity NJM work and NJM during landing compared to landings following forefoot jumps.     

The written assignments in correspondence education. Effects of reducing turn‐around time. An experimental study

An essential feature in correspondence education is the two‐way communication between teacher and student and a central feature of this is the written assignments. Even if the postal services are quick, the handling of the assignments, correcting and commenting on them is bound to take some time. Studies by Sloan in 1965 and Saxe et al in 1966 suggested that the time element involved in the communication between teacher and student might be one of the main reasons for loss of interest and, ultimately, drop‐out.

The main purpose of the experiment reported here was to examine the effect of reducing the turn‐around time. Some statistical analyses in the original have been omitted in this translation. The approach cannot be taken as being representative of what the author's views on the subject would be a decade later.     

Book reviews

Distributed Learning: social and cultural approaches to practiceEdited by Mary R. Lea and Kathy Nicoll, 2002 RoutledgeFalmer 214 pp., £19.99 ISBN 0 415 26809 5Distributed Learning: social and cultural approaches to practice, edited by Mary R. Lea and Kathy Nicoll, is published as part of the Open University UK course Understanding Distributed and Flexible Learning within the Postgraduate Programme in Open and Distance Education. The book comprises of 12 chapters written by authors from different academic backgrounds. They draw on their extensive practical experiences to present and reflect on a number of conceptual models and describe best practices in distributed learning. The volume is aimed at practitioners who intend to use technology in a higher education setting and also helps those who may have been using it for a few years to rethink their approaches to online learning and teaching. The reader is introduced to several theoretical concepts based on different disciplines and perspectives, e.g. anthropology, psychology, sociology, philosophy, economics and pedagogy. The specific focus is on the social and cultural aspects of learning. What does the term distributed learning mean? It describes practices on the continuum between traditional distance education and campus-based face-to-face education (cf. flexible learning, blended learning). With the proliferation of information and communications technology (ICT) in campus-based educational settings the boundaries between distance education and face-to-face education are fading. More and more traditional campus-based universities are providing access to higher education in a distance learning format. In fact, ICTs facilitate contact over a distance. Some authors even speak of a convergence between the two forms of education (Mills &;Tait, 1999). Campus-based institutions cannot deny their tradition: they insist that contact sessions are essential for successful internet-based independent learning, although distance education with its high quality pre-prepared study materials and tutorial (online) support has proven otherwise. This is what models for blended learning try to illuminate: the appropriate mix of face-to-face and distance teaching approaches. A strength of the book is that the authors come from both distance teaching as well as campus-based institutions and thus different views on the continuum are presented.